Bug Summary

File:lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
Warning:line 2361, column 24
The left operand of '>=' is a garbage value

Annotated Source Code

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clang -cc1 -triple x86_64-pc-linux-gnu -analyze -disable-free -disable-llvm-verifier -discard-value-names -main-file-name SimpleLoopUnswitch.cpp -analyzer-store=region -analyzer-opt-analyze-nested-blocks -analyzer-eagerly-assume -analyzer-checker=core -analyzer-checker=apiModeling -analyzer-checker=unix -analyzer-checker=deadcode -analyzer-checker=cplusplus -analyzer-checker=security.insecureAPI.UncheckedReturn -analyzer-checker=security.insecureAPI.getpw -analyzer-checker=security.insecureAPI.gets -analyzer-checker=security.insecureAPI.mktemp -analyzer-checker=security.insecureAPI.mkstemp -analyzer-checker=security.insecureAPI.vfork -analyzer-checker=nullability.NullPassedToNonnull -analyzer-checker=nullability.NullReturnedFromNonnull -analyzer-output plist -w -mrelocation-model pic -pic-level 2 -mthread-model posix -fmath-errno -masm-verbose -mconstructor-aliases -munwind-tables -fuse-init-array -target-cpu x86-64 -dwarf-column-info -debugger-tuning=gdb -momit-leaf-frame-pointer -ffunction-sections -fdata-sections -resource-dir /usr/lib/llvm-7/lib/clang/7.0.0 -D _DEBUG -D _GNU_SOURCE -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D __STDC_LIMIT_MACROS -I /build/llvm-toolchain-snapshot-7~svn338205/build-llvm/lib/Transforms/Scalar -I /build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar -I /build/llvm-toolchain-snapshot-7~svn338205/build-llvm/include -I /build/llvm-toolchain-snapshot-7~svn338205/include -U NDEBUG -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/x86_64-linux-gnu/c++/8 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/x86_64-linux-gnu/c++/8 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/backward -internal-isystem /usr/include/clang/7.0.0/include/ -internal-isystem /usr/local/include -internal-isystem /usr/lib/llvm-7/lib/clang/7.0.0/include -internal-externc-isystem /usr/lib/gcc/x86_64-linux-gnu/8/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -O2 -Wno-unused-parameter -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -Wno-maybe-uninitialized -Wno-class-memaccess -Wno-comment -std=c++11 -fdeprecated-macro -fdebug-compilation-dir /build/llvm-toolchain-snapshot-7~svn338205/build-llvm/lib/Transforms/Scalar -ferror-limit 19 -fmessage-length 0 -fvisibility-inlines-hidden -fobjc-runtime=gcc -fdiagnostics-show-option -vectorize-loops -vectorize-slp -analyzer-output=html -analyzer-config stable-report-filename=true -o /tmp/scan-build-2018-07-29-043837-17923-1 -x c++ /build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp -faddrsig
1///===- SimpleLoopUnswitch.cpp - Hoist loop-invariant control flow ---------===//
2//
3// The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9
10#include "llvm/Transforms/Scalar/SimpleLoopUnswitch.h"
11#include "llvm/ADT/DenseMap.h"
12#include "llvm/ADT/STLExtras.h"
13#include "llvm/ADT/Sequence.h"
14#include "llvm/ADT/SetVector.h"
15#include "llvm/ADT/SmallPtrSet.h"
16#include "llvm/ADT/SmallVector.h"
17#include "llvm/ADT/Statistic.h"
18#include "llvm/ADT/Twine.h"
19#include "llvm/Analysis/AssumptionCache.h"
20#include "llvm/Analysis/CFG.h"
21#include "llvm/Analysis/CodeMetrics.h"
22#include "llvm/Analysis/InstructionSimplify.h"
23#include "llvm/Analysis/LoopAnalysisManager.h"
24#include "llvm/Analysis/LoopInfo.h"
25#include "llvm/Analysis/LoopIterator.h"
26#include "llvm/Analysis/LoopPass.h"
27#include "llvm/Analysis/Utils/Local.h"
28#include "llvm/IR/BasicBlock.h"
29#include "llvm/IR/Constant.h"
30#include "llvm/IR/Constants.h"
31#include "llvm/IR/Dominators.h"
32#include "llvm/IR/Function.h"
33#include "llvm/IR/InstrTypes.h"
34#include "llvm/IR/Instruction.h"
35#include "llvm/IR/Instructions.h"
36#include "llvm/IR/IntrinsicInst.h"
37#include "llvm/IR/Use.h"
38#include "llvm/IR/Value.h"
39#include "llvm/Pass.h"
40#include "llvm/Support/Casting.h"
41#include "llvm/Support/Debug.h"
42#include "llvm/Support/ErrorHandling.h"
43#include "llvm/Support/GenericDomTree.h"
44#include "llvm/Support/raw_ostream.h"
45#include "llvm/Transforms/Scalar/SimpleLoopUnswitch.h"
46#include "llvm/Transforms/Utils/BasicBlockUtils.h"
47#include "llvm/Transforms/Utils/Cloning.h"
48#include "llvm/Transforms/Utils/LoopUtils.h"
49#include "llvm/Transforms/Utils/ValueMapper.h"
50#include <algorithm>
51#include <cassert>
52#include <iterator>
53#include <numeric>
54#include <utility>
55
56#define DEBUG_TYPE"simple-loop-unswitch" "simple-loop-unswitch"
57
58using namespace llvm;
59
60STATISTIC(NumBranches, "Number of branches unswitched")static llvm::Statistic NumBranches = {"simple-loop-unswitch",
"NumBranches", "Number of branches unswitched", {0}, {false}
}
;
61STATISTIC(NumSwitches, "Number of switches unswitched")static llvm::Statistic NumSwitches = {"simple-loop-unswitch",
"NumSwitches", "Number of switches unswitched", {0}, {false}
}
;
62STATISTIC(NumTrivial, "Number of unswitches that are trivial")static llvm::Statistic NumTrivial = {"simple-loop-unswitch", "NumTrivial"
, "Number of unswitches that are trivial", {0}, {false}}
;
63
64static cl::opt<bool> EnableNonTrivialUnswitch(
65 "enable-nontrivial-unswitch", cl::init(false), cl::Hidden,
66 cl::desc("Forcibly enables non-trivial loop unswitching rather than "
67 "following the configuration passed into the pass."));
68
69static cl::opt<int>
70 UnswitchThreshold("unswitch-threshold", cl::init(50), cl::Hidden,
71 cl::desc("The cost threshold for unswitching a loop."));
72
73/// Collect all of the loop invariant input values transitively used by the
74/// homogeneous instruction graph from a given root.
75///
76/// This essentially walks from a root recursively through loop variant operands
77/// which have the exact same opcode and finds all inputs which are loop
78/// invariant. For some operations these can be re-associated and unswitched out
79/// of the loop entirely.
80static TinyPtrVector<Value *>
81collectHomogenousInstGraphLoopInvariants(Loop &L, Instruction &Root,
82 LoopInfo &LI) {
83 assert(!L.isLoopInvariant(&Root) &&(static_cast <bool> (!L.isLoopInvariant(&Root) &&
"Only need to walk the graph if root itself is not invariant."
) ? void (0) : __assert_fail ("!L.isLoopInvariant(&Root) && \"Only need to walk the graph if root itself is not invariant.\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 84, __extension__ __PRETTY_FUNCTION__))
84 "Only need to walk the graph if root itself is not invariant.")(static_cast <bool> (!L.isLoopInvariant(&Root) &&
"Only need to walk the graph if root itself is not invariant."
) ? void (0) : __assert_fail ("!L.isLoopInvariant(&Root) && \"Only need to walk the graph if root itself is not invariant.\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 84, __extension__ __PRETTY_FUNCTION__))
;
85 TinyPtrVector<Value *> Invariants;
86
87 // Build a worklist and recurse through operators collecting invariants.
88 SmallVector<Instruction *, 4> Worklist;
89 SmallPtrSet<Instruction *, 8> Visited;
90 Worklist.push_back(&Root);
91 Visited.insert(&Root);
92 do {
93 Instruction &I = *Worklist.pop_back_val();
94 for (Value *OpV : I.operand_values()) {
95 // Skip constants as unswitching isn't interesting for them.
96 if (isa<Constant>(OpV))
97 continue;
98
99 // Add it to our result if loop invariant.
100 if (L.isLoopInvariant(OpV)) {
101 Invariants.push_back(OpV);
102 continue;
103 }
104
105 // If not an instruction with the same opcode, nothing we can do.
106 Instruction *OpI = dyn_cast<Instruction>(OpV);
107 if (!OpI || OpI->getOpcode() != Root.getOpcode())
108 continue;
109
110 // Visit this operand.
111 if (Visited.insert(OpI).second)
112 Worklist.push_back(OpI);
113 }
114 } while (!Worklist.empty());
115
116 return Invariants;
117}
118
119static void replaceLoopInvariantUses(Loop &L, Value *Invariant,
120 Constant &Replacement) {
121 assert(!isa<Constant>(Invariant) && "Why are we unswitching on a constant?")(static_cast <bool> (!isa<Constant>(Invariant) &&
"Why are we unswitching on a constant?") ? void (0) : __assert_fail
("!isa<Constant>(Invariant) && \"Why are we unswitching on a constant?\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 121, __extension__ __PRETTY_FUNCTION__))
;
122
123 // Replace uses of LIC in the loop with the given constant.
124 for (auto UI = Invariant->use_begin(), UE = Invariant->use_end(); UI != UE;) {
125 // Grab the use and walk past it so we can clobber it in the use list.
126 Use *U = &*UI++;
127 Instruction *UserI = dyn_cast<Instruction>(U->getUser());
128
129 // Replace this use within the loop body.
130 if (UserI && L.contains(UserI))
131 U->set(&Replacement);
132 }
133}
134
135/// Check that all the LCSSA PHI nodes in the loop exit block have trivial
136/// incoming values along this edge.
137static bool areLoopExitPHIsLoopInvariant(Loop &L, BasicBlock &ExitingBB,
138 BasicBlock &ExitBB) {
139 for (Instruction &I : ExitBB) {
140 auto *PN = dyn_cast<PHINode>(&I);
141 if (!PN)
142 // No more PHIs to check.
143 return true;
144
145 // If the incoming value for this edge isn't loop invariant the unswitch
146 // won't be trivial.
147 if (!L.isLoopInvariant(PN->getIncomingValueForBlock(&ExitingBB)))
148 return false;
149 }
150 llvm_unreachable("Basic blocks should never be empty!")::llvm::llvm_unreachable_internal("Basic blocks should never be empty!"
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 150)
;
151}
152
153/// Insert code to test a set of loop invariant values, and conditionally branch
154/// on them.
155static void buildPartialUnswitchConditionalBranch(BasicBlock &BB,
156 ArrayRef<Value *> Invariants,
157 bool Direction,
158 BasicBlock &UnswitchedSucc,
159 BasicBlock &NormalSucc) {
160 IRBuilder<> IRB(&BB);
161 Value *Cond = Invariants.front();
162 for (Value *Invariant :
163 make_range(std::next(Invariants.begin()), Invariants.end()))
164 if (Direction)
165 Cond = IRB.CreateOr(Cond, Invariant);
166 else
167 Cond = IRB.CreateAnd(Cond, Invariant);
168
169 IRB.CreateCondBr(Cond, Direction ? &UnswitchedSucc : &NormalSucc,
170 Direction ? &NormalSucc : &UnswitchedSucc);
171}
172
173/// Rewrite the PHI nodes in an unswitched loop exit basic block.
174///
175/// Requires that the loop exit and unswitched basic block are the same, and
176/// that the exiting block was a unique predecessor of that block. Rewrites the
177/// PHI nodes in that block such that what were LCSSA PHI nodes become trivial
178/// PHI nodes from the old preheader that now contains the unswitched
179/// terminator.
180static void rewritePHINodesForUnswitchedExitBlock(BasicBlock &UnswitchedBB,
181 BasicBlock &OldExitingBB,
182 BasicBlock &OldPH) {
183 for (PHINode &PN : UnswitchedBB.phis()) {
184 // When the loop exit is directly unswitched we just need to update the
185 // incoming basic block. We loop to handle weird cases with repeated
186 // incoming blocks, but expect to typically only have one operand here.
187 for (auto i : seq<int>(0, PN.getNumOperands())) {
188 assert(PN.getIncomingBlock(i) == &OldExitingBB &&(static_cast <bool> (PN.getIncomingBlock(i) == &OldExitingBB
&& "Found incoming block different from unique predecessor!"
) ? void (0) : __assert_fail ("PN.getIncomingBlock(i) == &OldExitingBB && \"Found incoming block different from unique predecessor!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 189, __extension__ __PRETTY_FUNCTION__))
189 "Found incoming block different from unique predecessor!")(static_cast <bool> (PN.getIncomingBlock(i) == &OldExitingBB
&& "Found incoming block different from unique predecessor!"
) ? void (0) : __assert_fail ("PN.getIncomingBlock(i) == &OldExitingBB && \"Found incoming block different from unique predecessor!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 189, __extension__ __PRETTY_FUNCTION__))
;
190 PN.setIncomingBlock(i, &OldPH);
191 }
192 }
193}
194
195/// Rewrite the PHI nodes in the loop exit basic block and the split off
196/// unswitched block.
197///
198/// Because the exit block remains an exit from the loop, this rewrites the
199/// LCSSA PHI nodes in it to remove the unswitched edge and introduces PHI
200/// nodes into the unswitched basic block to select between the value in the
201/// old preheader and the loop exit.
202static void rewritePHINodesForExitAndUnswitchedBlocks(BasicBlock &ExitBB,
203 BasicBlock &UnswitchedBB,
204 BasicBlock &OldExitingBB,
205 BasicBlock &OldPH,
206 bool FullUnswitch) {
207 assert(&ExitBB != &UnswitchedBB &&(static_cast <bool> (&ExitBB != &UnswitchedBB &&
"Must have different loop exit and unswitched blocks!") ? void
(0) : __assert_fail ("&ExitBB != &UnswitchedBB && \"Must have different loop exit and unswitched blocks!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 208, __extension__ __PRETTY_FUNCTION__))
208 "Must have different loop exit and unswitched blocks!")(static_cast <bool> (&ExitBB != &UnswitchedBB &&
"Must have different loop exit and unswitched blocks!") ? void
(0) : __assert_fail ("&ExitBB != &UnswitchedBB && \"Must have different loop exit and unswitched blocks!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 208, __extension__ __PRETTY_FUNCTION__))
;
209 Instruction *InsertPt = &*UnswitchedBB.begin();
210 for (PHINode &PN : ExitBB.phis()) {
211 auto *NewPN = PHINode::Create(PN.getType(), /*NumReservedValues*/ 2,
212 PN.getName() + ".split", InsertPt);
213
214 // Walk backwards over the old PHI node's inputs to minimize the cost of
215 // removing each one. We have to do this weird loop manually so that we
216 // create the same number of new incoming edges in the new PHI as we expect
217 // each case-based edge to be included in the unswitched switch in some
218 // cases.
219 // FIXME: This is really, really gross. It would be much cleaner if LLVM
220 // allowed us to create a single entry for a predecessor block without
221 // having separate entries for each "edge" even though these edges are
222 // required to produce identical results.
223 for (int i = PN.getNumIncomingValues() - 1; i >= 0; --i) {
224 if (PN.getIncomingBlock(i) != &OldExitingBB)
225 continue;
226
227 Value *Incoming = PN.getIncomingValue(i);
228 if (FullUnswitch)
229 // No more edge from the old exiting block to the exit block.
230 PN.removeIncomingValue(i);
231
232 NewPN->addIncoming(Incoming, &OldPH);
233 }
234
235 // Now replace the old PHI with the new one and wire the old one in as an
236 // input to the new one.
237 PN.replaceAllUsesWith(NewPN);
238 NewPN->addIncoming(&PN, &ExitBB);
239 }
240}
241
242/// Hoist the current loop up to the innermost loop containing a remaining exit.
243///
244/// Because we've removed an exit from the loop, we may have changed the set of
245/// loops reachable and need to move the current loop up the loop nest or even
246/// to an entirely separate nest.
247static void hoistLoopToNewParent(Loop &L, BasicBlock &Preheader,
248 DominatorTree &DT, LoopInfo &LI) {
249 // If the loop is already at the top level, we can't hoist it anywhere.
250 Loop *OldParentL = L.getParentLoop();
251 if (!OldParentL)
252 return;
253
254 SmallVector<BasicBlock *, 4> Exits;
255 L.getExitBlocks(Exits);
256 Loop *NewParentL = nullptr;
257 for (auto *ExitBB : Exits)
258 if (Loop *ExitL = LI.getLoopFor(ExitBB))
259 if (!NewParentL || NewParentL->contains(ExitL))
260 NewParentL = ExitL;
261
262 if (NewParentL == OldParentL)
263 return;
264
265 // The new parent loop (if different) should always contain the old one.
266 if (NewParentL)
267 assert(NewParentL->contains(OldParentL) &&(static_cast <bool> (NewParentL->contains(OldParentL
) && "Can only hoist this loop up the nest!") ? void (
0) : __assert_fail ("NewParentL->contains(OldParentL) && \"Can only hoist this loop up the nest!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 268, __extension__ __PRETTY_FUNCTION__))
268 "Can only hoist this loop up the nest!")(static_cast <bool> (NewParentL->contains(OldParentL
) && "Can only hoist this loop up the nest!") ? void (
0) : __assert_fail ("NewParentL->contains(OldParentL) && \"Can only hoist this loop up the nest!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 268, __extension__ __PRETTY_FUNCTION__))
;
269
270 // The preheader will need to move with the body of this loop. However,
271 // because it isn't in this loop we also need to update the primary loop map.
272 assert(OldParentL == LI.getLoopFor(&Preheader) &&(static_cast <bool> (OldParentL == LI.getLoopFor(&Preheader
) && "Parent loop of this loop should contain this loop's preheader!"
) ? void (0) : __assert_fail ("OldParentL == LI.getLoopFor(&Preheader) && \"Parent loop of this loop should contain this loop's preheader!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 273, __extension__ __PRETTY_FUNCTION__))
273 "Parent loop of this loop should contain this loop's preheader!")(static_cast <bool> (OldParentL == LI.getLoopFor(&Preheader
) && "Parent loop of this loop should contain this loop's preheader!"
) ? void (0) : __assert_fail ("OldParentL == LI.getLoopFor(&Preheader) && \"Parent loop of this loop should contain this loop's preheader!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 273, __extension__ __PRETTY_FUNCTION__))
;
274 LI.changeLoopFor(&Preheader, NewParentL);
275
276 // Remove this loop from its old parent.
277 OldParentL->removeChildLoop(&L);
278
279 // Add the loop either to the new parent or as a top-level loop.
280 if (NewParentL)
281 NewParentL->addChildLoop(&L);
282 else
283 LI.addTopLevelLoop(&L);
284
285 // Remove this loops blocks from the old parent and every other loop up the
286 // nest until reaching the new parent. Also update all of these
287 // no-longer-containing loops to reflect the nesting change.
288 for (Loop *OldContainingL = OldParentL; OldContainingL != NewParentL;
289 OldContainingL = OldContainingL->getParentLoop()) {
290 llvm::erase_if(OldContainingL->getBlocksVector(),
291 [&](const BasicBlock *BB) {
292 return BB == &Preheader || L.contains(BB);
293 });
294
295 OldContainingL->getBlocksSet().erase(&Preheader);
296 for (BasicBlock *BB : L.blocks())
297 OldContainingL->getBlocksSet().erase(BB);
298
299 // Because we just hoisted a loop out of this one, we have essentially
300 // created new exit paths from it. That means we need to form LCSSA PHI
301 // nodes for values used in the no-longer-nested loop.
302 formLCSSA(*OldContainingL, DT, &LI, nullptr);
303
304 // We shouldn't need to form dedicated exits because the exit introduced
305 // here is the (just split by unswitching) preheader. As such, it is
306 // necessarily dedicated.
307 assert(OldContainingL->hasDedicatedExits() &&(static_cast <bool> (OldContainingL->hasDedicatedExits
() && "Unexpected predecessor of hoisted loop preheader!"
) ? void (0) : __assert_fail ("OldContainingL->hasDedicatedExits() && \"Unexpected predecessor of hoisted loop preheader!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 308, __extension__ __PRETTY_FUNCTION__))
308 "Unexpected predecessor of hoisted loop preheader!")(static_cast <bool> (OldContainingL->hasDedicatedExits
() && "Unexpected predecessor of hoisted loop preheader!"
) ? void (0) : __assert_fail ("OldContainingL->hasDedicatedExits() && \"Unexpected predecessor of hoisted loop preheader!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 308, __extension__ __PRETTY_FUNCTION__))
;
309 }
310}
311
312/// Unswitch a trivial branch if the condition is loop invariant.
313///
314/// This routine should only be called when loop code leading to the branch has
315/// been validated as trivial (no side effects). This routine checks if the
316/// condition is invariant and one of the successors is a loop exit. This
317/// allows us to unswitch without duplicating the loop, making it trivial.
318///
319/// If this routine fails to unswitch the branch it returns false.
320///
321/// If the branch can be unswitched, this routine splits the preheader and
322/// hoists the branch above that split. Preserves loop simplified form
323/// (splitting the exit block as necessary). It simplifies the branch within
324/// the loop to an unconditional branch but doesn't remove it entirely. Further
325/// cleanup can be done with some simplify-cfg like pass.
326///
327/// If `SE` is not null, it will be updated based on the potential loop SCEVs
328/// invalidated by this.
329static bool unswitchTrivialBranch(Loop &L, BranchInst &BI, DominatorTree &DT,
330 LoopInfo &LI, ScalarEvolution *SE) {
331 assert(BI.isConditional() && "Can only unswitch a conditional branch!")(static_cast <bool> (BI.isConditional() && "Can only unswitch a conditional branch!"
) ? void (0) : __assert_fail ("BI.isConditional() && \"Can only unswitch a conditional branch!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 331, __extension__ __PRETTY_FUNCTION__))
;
332 LLVM_DEBUG(dbgs() << " Trying to unswitch branch: " << BI << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << " Trying to unswitch branch: "
<< BI << "\n"; } } while (false)
;
333
334 // The loop invariant values that we want to unswitch.
335 TinyPtrVector<Value *> Invariants;
336
337 // When true, we're fully unswitching the branch rather than just unswitching
338 // some input conditions to the branch.
339 bool FullUnswitch = false;
340
341 if (L.isLoopInvariant(BI.getCondition())) {
342 Invariants.push_back(BI.getCondition());
343 FullUnswitch = true;
344 } else {
345 if (auto *CondInst = dyn_cast<Instruction>(BI.getCondition()))
346 Invariants = collectHomogenousInstGraphLoopInvariants(L, *CondInst, LI);
347 if (Invariants.empty())
348 // Couldn't find invariant inputs!
349 return false;
350 }
351
352 // Check that one of the branch's successors exits, and which one.
353 bool ExitDirection = true;
354 int LoopExitSuccIdx = 0;
355 auto *LoopExitBB = BI.getSuccessor(0);
356 if (L.contains(LoopExitBB)) {
357 ExitDirection = false;
358 LoopExitSuccIdx = 1;
359 LoopExitBB = BI.getSuccessor(1);
360 if (L.contains(LoopExitBB))
361 return false;
362 }
363 auto *ContinueBB = BI.getSuccessor(1 - LoopExitSuccIdx);
364 auto *ParentBB = BI.getParent();
365 if (!areLoopExitPHIsLoopInvariant(L, *ParentBB, *LoopExitBB))
366 return false;
367
368 // When unswitching only part of the branch's condition, we need the exit
369 // block to be reached directly from the partially unswitched input. This can
370 // be done when the exit block is along the true edge and the branch condition
371 // is a graph of `or` operations, or the exit block is along the false edge
372 // and the condition is a graph of `and` operations.
373 if (!FullUnswitch) {
374 if (ExitDirection) {
375 if (cast<Instruction>(BI.getCondition())->getOpcode() != Instruction::Or)
376 return false;
377 } else {
378 if (cast<Instruction>(BI.getCondition())->getOpcode() != Instruction::And)
379 return false;
380 }
381 }
382
383 LLVM_DEBUG({do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { { dbgs() << " unswitching trivial invariant conditions for: "
<< BI << "\n"; for (Value *Invariant : Invariants
) { dbgs() << " " << *Invariant << " == true"
; if (Invariant != Invariants.back()) dbgs() << " ||"; dbgs
() << "\n"; } }; } } while (false)
384 dbgs() << " unswitching trivial invariant conditions for: " << BIdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { { dbgs() << " unswitching trivial invariant conditions for: "
<< BI << "\n"; for (Value *Invariant : Invariants
) { dbgs() << " " << *Invariant << " == true"
; if (Invariant != Invariants.back()) dbgs() << " ||"; dbgs
() << "\n"; } }; } } while (false)
385 << "\n";do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { { dbgs() << " unswitching trivial invariant conditions for: "
<< BI << "\n"; for (Value *Invariant : Invariants
) { dbgs() << " " << *Invariant << " == true"
; if (Invariant != Invariants.back()) dbgs() << " ||"; dbgs
() << "\n"; } }; } } while (false)
386 for (Value *Invariant : Invariants) {do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { { dbgs() << " unswitching trivial invariant conditions for: "
<< BI << "\n"; for (Value *Invariant : Invariants
) { dbgs() << " " << *Invariant << " == true"
; if (Invariant != Invariants.back()) dbgs() << " ||"; dbgs
() << "\n"; } }; } } while (false)
387 dbgs() << " " << *Invariant << " == true";do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { { dbgs() << " unswitching trivial invariant conditions for: "
<< BI << "\n"; for (Value *Invariant : Invariants
) { dbgs() << " " << *Invariant << " == true"
; if (Invariant != Invariants.back()) dbgs() << " ||"; dbgs
() << "\n"; } }; } } while (false)
388 if (Invariant != Invariants.back())do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { { dbgs() << " unswitching trivial invariant conditions for: "
<< BI << "\n"; for (Value *Invariant : Invariants
) { dbgs() << " " << *Invariant << " == true"
; if (Invariant != Invariants.back()) dbgs() << " ||"; dbgs
() << "\n"; } }; } } while (false)
389 dbgs() << " ||";do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { { dbgs() << " unswitching trivial invariant conditions for: "
<< BI << "\n"; for (Value *Invariant : Invariants
) { dbgs() << " " << *Invariant << " == true"
; if (Invariant != Invariants.back()) dbgs() << " ||"; dbgs
() << "\n"; } }; } } while (false)
390 dbgs() << "\n";do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { { dbgs() << " unswitching trivial invariant conditions for: "
<< BI << "\n"; for (Value *Invariant : Invariants
) { dbgs() << " " << *Invariant << " == true"
; if (Invariant != Invariants.back()) dbgs() << " ||"; dbgs
() << "\n"; } }; } } while (false)
391 }do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { { dbgs() << " unswitching trivial invariant conditions for: "
<< BI << "\n"; for (Value *Invariant : Invariants
) { dbgs() << " " << *Invariant << " == true"
; if (Invariant != Invariants.back()) dbgs() << " ||"; dbgs
() << "\n"; } }; } } while (false)
392 })do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { { dbgs() << " unswitching trivial invariant conditions for: "
<< BI << "\n"; for (Value *Invariant : Invariants
) { dbgs() << " " << *Invariant << " == true"
; if (Invariant != Invariants.back()) dbgs() << " ||"; dbgs
() << "\n"; } }; } } while (false)
;
393
394 // If we have scalar evolutions, we need to invalidate them including this
395 // loop and the loop containing the exit block.
396 if (SE) {
397 if (Loop *ExitL = LI.getLoopFor(LoopExitBB))
398 SE->forgetLoop(ExitL);
399 else
400 // Forget the entire nest as this exits the entire nest.
401 SE->forgetTopmostLoop(&L);
402 }
403
404 // Split the preheader, so that we know that there is a safe place to insert
405 // the conditional branch. We will change the preheader to have a conditional
406 // branch on LoopCond.
407 BasicBlock *OldPH = L.getLoopPreheader();
408 BasicBlock *NewPH = SplitEdge(OldPH, L.getHeader(), &DT, &LI);
409
410 // Now that we have a place to insert the conditional branch, create a place
411 // to branch to: this is the exit block out of the loop that we are
412 // unswitching. We need to split this if there are other loop predecessors.
413 // Because the loop is in simplified form, *any* other predecessor is enough.
414 BasicBlock *UnswitchedBB;
415 if (FullUnswitch && LoopExitBB->getUniquePredecessor()) {
416 assert(LoopExitBB->getUniquePredecessor() == BI.getParent() &&(static_cast <bool> (LoopExitBB->getUniquePredecessor
() == BI.getParent() && "A branch's parent isn't a predecessor!"
) ? void (0) : __assert_fail ("LoopExitBB->getUniquePredecessor() == BI.getParent() && \"A branch's parent isn't a predecessor!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 417, __extension__ __PRETTY_FUNCTION__))
417 "A branch's parent isn't a predecessor!")(static_cast <bool> (LoopExitBB->getUniquePredecessor
() == BI.getParent() && "A branch's parent isn't a predecessor!"
) ? void (0) : __assert_fail ("LoopExitBB->getUniquePredecessor() == BI.getParent() && \"A branch's parent isn't a predecessor!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 417, __extension__ __PRETTY_FUNCTION__))
;
418 UnswitchedBB = LoopExitBB;
419 } else {
420 UnswitchedBB = SplitBlock(LoopExitBB, &LoopExitBB->front(), &DT, &LI);
421 }
422
423 // Actually move the invariant uses into the unswitched position. If possible,
424 // we do this by moving the instructions, but when doing partial unswitching
425 // we do it by building a new merge of the values in the unswitched position.
426 OldPH->getTerminator()->eraseFromParent();
427 if (FullUnswitch) {
428 // If fully unswitching, we can use the existing branch instruction.
429 // Splice it into the old PH to gate reaching the new preheader and re-point
430 // its successors.
431 OldPH->getInstList().splice(OldPH->end(), BI.getParent()->getInstList(),
432 BI);
433 BI.setSuccessor(LoopExitSuccIdx, UnswitchedBB);
434 BI.setSuccessor(1 - LoopExitSuccIdx, NewPH);
435
436 // Create a new unconditional branch that will continue the loop as a new
437 // terminator.
438 BranchInst::Create(ContinueBB, ParentBB);
439 } else {
440 // Only unswitching a subset of inputs to the condition, so we will need to
441 // build a new branch that merges the invariant inputs.
442 if (ExitDirection)
443 assert(cast<Instruction>(BI.getCondition())->getOpcode() ==(static_cast <bool> (cast<Instruction>(BI.getCondition
())->getOpcode() == Instruction::Or && "Must have an `or` of `i1`s for the condition!"
) ? void (0) : __assert_fail ("cast<Instruction>(BI.getCondition())->getOpcode() == Instruction::Or && \"Must have an `or` of `i1`s for the condition!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 445, __extension__ __PRETTY_FUNCTION__))
444 Instruction::Or &&(static_cast <bool> (cast<Instruction>(BI.getCondition
())->getOpcode() == Instruction::Or && "Must have an `or` of `i1`s for the condition!"
) ? void (0) : __assert_fail ("cast<Instruction>(BI.getCondition())->getOpcode() == Instruction::Or && \"Must have an `or` of `i1`s for the condition!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 445, __extension__ __PRETTY_FUNCTION__))
445 "Must have an `or` of `i1`s for the condition!")(static_cast <bool> (cast<Instruction>(BI.getCondition
())->getOpcode() == Instruction::Or && "Must have an `or` of `i1`s for the condition!"
) ? void (0) : __assert_fail ("cast<Instruction>(BI.getCondition())->getOpcode() == Instruction::Or && \"Must have an `or` of `i1`s for the condition!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 445, __extension__ __PRETTY_FUNCTION__))
;
446 else
447 assert(cast<Instruction>(BI.getCondition())->getOpcode() ==(static_cast <bool> (cast<Instruction>(BI.getCondition
())->getOpcode() == Instruction::And && "Must have an `and` of `i1`s for the condition!"
) ? void (0) : __assert_fail ("cast<Instruction>(BI.getCondition())->getOpcode() == Instruction::And && \"Must have an `and` of `i1`s for the condition!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 449, __extension__ __PRETTY_FUNCTION__))
448 Instruction::And &&(static_cast <bool> (cast<Instruction>(BI.getCondition
())->getOpcode() == Instruction::And && "Must have an `and` of `i1`s for the condition!"
) ? void (0) : __assert_fail ("cast<Instruction>(BI.getCondition())->getOpcode() == Instruction::And && \"Must have an `and` of `i1`s for the condition!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 449, __extension__ __PRETTY_FUNCTION__))
449 "Must have an `and` of `i1`s for the condition!")(static_cast <bool> (cast<Instruction>(BI.getCondition
())->getOpcode() == Instruction::And && "Must have an `and` of `i1`s for the condition!"
) ? void (0) : __assert_fail ("cast<Instruction>(BI.getCondition())->getOpcode() == Instruction::And && \"Must have an `and` of `i1`s for the condition!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 449, __extension__ __PRETTY_FUNCTION__))
;
450 buildPartialUnswitchConditionalBranch(*OldPH, Invariants, ExitDirection,
451 *UnswitchedBB, *NewPH);
452 }
453
454 // Rewrite the relevant PHI nodes.
455 if (UnswitchedBB == LoopExitBB)
456 rewritePHINodesForUnswitchedExitBlock(*UnswitchedBB, *ParentBB, *OldPH);
457 else
458 rewritePHINodesForExitAndUnswitchedBlocks(*LoopExitBB, *UnswitchedBB,
459 *ParentBB, *OldPH, FullUnswitch);
460
461 // Now we need to update the dominator tree.
462 SmallVector<DominatorTree::UpdateType, 2> DTUpdates;
463 DTUpdates.push_back({DT.Insert, OldPH, UnswitchedBB});
464 if (FullUnswitch)
465 DTUpdates.push_back({DT.Delete, ParentBB, LoopExitBB});
466 DT.applyUpdates(DTUpdates);
467
468 // The constant we can replace all of our invariants with inside the loop
469 // body. If any of the invariants have a value other than this the loop won't
470 // be entered.
471 ConstantInt *Replacement = ExitDirection
472 ? ConstantInt::getFalse(BI.getContext())
473 : ConstantInt::getTrue(BI.getContext());
474
475 // Since this is an i1 condition we can also trivially replace uses of it
476 // within the loop with a constant.
477 for (Value *Invariant : Invariants)
478 replaceLoopInvariantUses(L, Invariant, *Replacement);
479
480 // If this was full unswitching, we may have changed the nesting relationship
481 // for this loop so hoist it to its correct parent if needed.
482 if (FullUnswitch)
483 hoistLoopToNewParent(L, *NewPH, DT, LI);
484
485 ++NumTrivial;
486 ++NumBranches;
487 return true;
488}
489
490/// Unswitch a trivial switch if the condition is loop invariant.
491///
492/// This routine should only be called when loop code leading to the switch has
493/// been validated as trivial (no side effects). This routine checks if the
494/// condition is invariant and that at least one of the successors is a loop
495/// exit. This allows us to unswitch without duplicating the loop, making it
496/// trivial.
497///
498/// If this routine fails to unswitch the switch it returns false.
499///
500/// If the switch can be unswitched, this routine splits the preheader and
501/// copies the switch above that split. If the default case is one of the
502/// exiting cases, it copies the non-exiting cases and points them at the new
503/// preheader. If the default case is not exiting, it copies the exiting cases
504/// and points the default at the preheader. It preserves loop simplified form
505/// (splitting the exit blocks as necessary). It simplifies the switch within
506/// the loop by removing now-dead cases. If the default case is one of those
507/// unswitched, it replaces its destination with a new basic block containing
508/// only unreachable. Such basic blocks, while technically loop exits, are not
509/// considered for unswitching so this is a stable transform and the same
510/// switch will not be revisited. If after unswitching there is only a single
511/// in-loop successor, the switch is further simplified to an unconditional
512/// branch. Still more cleanup can be done with some simplify-cfg like pass.
513///
514/// If `SE` is not null, it will be updated based on the potential loop SCEVs
515/// invalidated by this.
516static bool unswitchTrivialSwitch(Loop &L, SwitchInst &SI, DominatorTree &DT,
517 LoopInfo &LI, ScalarEvolution *SE) {
518 LLVM_DEBUG(dbgs() << " Trying to unswitch switch: " << SI << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << " Trying to unswitch switch: "
<< SI << "\n"; } } while (false)
;
519 Value *LoopCond = SI.getCondition();
520
521 // If this isn't switching on an invariant condition, we can't unswitch it.
522 if (!L.isLoopInvariant(LoopCond))
523 return false;
524
525 auto *ParentBB = SI.getParent();
526
527 SmallVector<int, 4> ExitCaseIndices;
528 for (auto Case : SI.cases()) {
529 auto *SuccBB = Case.getCaseSuccessor();
530 if (!L.contains(SuccBB) &&
531 areLoopExitPHIsLoopInvariant(L, *ParentBB, *SuccBB))
532 ExitCaseIndices.push_back(Case.getCaseIndex());
533 }
534 BasicBlock *DefaultExitBB = nullptr;
535 if (!L.contains(SI.getDefaultDest()) &&
536 areLoopExitPHIsLoopInvariant(L, *ParentBB, *SI.getDefaultDest()) &&
537 !isa<UnreachableInst>(SI.getDefaultDest()->getTerminator()))
538 DefaultExitBB = SI.getDefaultDest();
539 else if (ExitCaseIndices.empty())
540 return false;
541
542 LLVM_DEBUG(dbgs() << " unswitching trivial cases...\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << " unswitching trivial cases...\n"
; } } while (false)
;
543
544 // We may need to invalidate SCEVs for the outermost loop reached by any of
545 // the exits.
546 Loop *OuterL = &L;
547
548 if (DefaultExitBB) {
549 // Clear out the default destination temporarily to allow accurate
550 // predecessor lists to be examined below.
551 SI.setDefaultDest(nullptr);
552 // Check the loop containing this exit.
553 Loop *ExitL = LI.getLoopFor(DefaultExitBB);
554 if (!ExitL || ExitL->contains(OuterL))
555 OuterL = ExitL;
556 }
557
558 // Store the exit cases into a separate data structure and remove them from
559 // the switch.
560 SmallVector<std::pair<ConstantInt *, BasicBlock *>, 4> ExitCases;
561 ExitCases.reserve(ExitCaseIndices.size());
562 // We walk the case indices backwards so that we remove the last case first
563 // and don't disrupt the earlier indices.
564 for (unsigned Index : reverse(ExitCaseIndices)) {
565 auto CaseI = SI.case_begin() + Index;
566 // Compute the outer loop from this exit.
567 Loop *ExitL = LI.getLoopFor(CaseI->getCaseSuccessor());
568 if (!ExitL || ExitL->contains(OuterL))
569 OuterL = ExitL;
570 // Save the value of this case.
571 ExitCases.push_back({CaseI->getCaseValue(), CaseI->getCaseSuccessor()});
572 // Delete the unswitched cases.
573 SI.removeCase(CaseI);
574 }
575
576 if (SE) {
577 if (OuterL)
578 SE->forgetLoop(OuterL);
579 else
580 SE->forgetTopmostLoop(&L);
581 }
582
583 // Check if after this all of the remaining cases point at the same
584 // successor.
585 BasicBlock *CommonSuccBB = nullptr;
586 if (SI.getNumCases() > 0 &&
587 std::all_of(std::next(SI.case_begin()), SI.case_end(),
588 [&SI](const SwitchInst::CaseHandle &Case) {
589 return Case.getCaseSuccessor() ==
590 SI.case_begin()->getCaseSuccessor();
591 }))
592 CommonSuccBB = SI.case_begin()->getCaseSuccessor();
593 if (!DefaultExitBB) {
594 // If we're not unswitching the default, we need it to match any cases to
595 // have a common successor or if we have no cases it is the common
596 // successor.
597 if (SI.getNumCases() == 0)
598 CommonSuccBB = SI.getDefaultDest();
599 else if (SI.getDefaultDest() != CommonSuccBB)
600 CommonSuccBB = nullptr;
601 }
602
603 // Split the preheader, so that we know that there is a safe place to insert
604 // the switch.
605 BasicBlock *OldPH = L.getLoopPreheader();
606 BasicBlock *NewPH = SplitEdge(OldPH, L.getHeader(), &DT, &LI);
607 OldPH->getTerminator()->eraseFromParent();
608
609 // Now add the unswitched switch.
610 auto *NewSI = SwitchInst::Create(LoopCond, NewPH, ExitCases.size(), OldPH);
611
612 // Rewrite the IR for the unswitched basic blocks. This requires two steps.
613 // First, we split any exit blocks with remaining in-loop predecessors. Then
614 // we update the PHIs in one of two ways depending on if there was a split.
615 // We walk in reverse so that we split in the same order as the cases
616 // appeared. This is purely for convenience of reading the resulting IR, but
617 // it doesn't cost anything really.
618 SmallPtrSet<BasicBlock *, 2> UnswitchedExitBBs;
619 SmallDenseMap<BasicBlock *, BasicBlock *, 2> SplitExitBBMap;
620 // Handle the default exit if necessary.
621 // FIXME: It'd be great if we could merge this with the loop below but LLVM's
622 // ranges aren't quite powerful enough yet.
623 if (DefaultExitBB) {
624 if (pred_empty(DefaultExitBB)) {
625 UnswitchedExitBBs.insert(DefaultExitBB);
626 rewritePHINodesForUnswitchedExitBlock(*DefaultExitBB, *ParentBB, *OldPH);
627 } else {
628 auto *SplitBB =
629 SplitBlock(DefaultExitBB, &DefaultExitBB->front(), &DT, &LI);
630 rewritePHINodesForExitAndUnswitchedBlocks(
631 *DefaultExitBB, *SplitBB, *ParentBB, *OldPH, /*FullUnswitch*/ true);
632 DefaultExitBB = SplitExitBBMap[DefaultExitBB] = SplitBB;
633 }
634 }
635 // Note that we must use a reference in the for loop so that we update the
636 // container.
637 for (auto &CasePair : reverse(ExitCases)) {
638 // Grab a reference to the exit block in the pair so that we can update it.
639 BasicBlock *ExitBB = CasePair.second;
640
641 // If this case is the last edge into the exit block, we can simply reuse it
642 // as it will no longer be a loop exit. No mapping necessary.
643 if (pred_empty(ExitBB)) {
644 // Only rewrite once.
645 if (UnswitchedExitBBs.insert(ExitBB).second)
646 rewritePHINodesForUnswitchedExitBlock(*ExitBB, *ParentBB, *OldPH);
647 continue;
648 }
649
650 // Otherwise we need to split the exit block so that we retain an exit
651 // block from the loop and a target for the unswitched condition.
652 BasicBlock *&SplitExitBB = SplitExitBBMap[ExitBB];
653 if (!SplitExitBB) {
654 // If this is the first time we see this, do the split and remember it.
655 SplitExitBB = SplitBlock(ExitBB, &ExitBB->front(), &DT, &LI);
656 rewritePHINodesForExitAndUnswitchedBlocks(
657 *ExitBB, *SplitExitBB, *ParentBB, *OldPH, /*FullUnswitch*/ true);
658 }
659 // Update the case pair to point to the split block.
660 CasePair.second = SplitExitBB;
661 }
662
663 // Now add the unswitched cases. We do this in reverse order as we built them
664 // in reverse order.
665 for (auto CasePair : reverse(ExitCases)) {
666 ConstantInt *CaseVal = CasePair.first;
667 BasicBlock *UnswitchedBB = CasePair.second;
668
669 NewSI->addCase(CaseVal, UnswitchedBB);
670 }
671
672 // If the default was unswitched, re-point it and add explicit cases for
673 // entering the loop.
674 if (DefaultExitBB) {
675 NewSI->setDefaultDest(DefaultExitBB);
676
677 // We removed all the exit cases, so we just copy the cases to the
678 // unswitched switch.
679 for (auto Case : SI.cases())
680 NewSI->addCase(Case.getCaseValue(), NewPH);
681 }
682
683 // If we ended up with a common successor for every path through the switch
684 // after unswitching, rewrite it to an unconditional branch to make it easy
685 // to recognize. Otherwise we potentially have to recognize the default case
686 // pointing at unreachable and other complexity.
687 if (CommonSuccBB) {
688 BasicBlock *BB = SI.getParent();
689 // We may have had multiple edges to this common successor block, so remove
690 // them as predecessors. We skip the first one, either the default or the
691 // actual first case.
692 bool SkippedFirst = DefaultExitBB == nullptr;
693 for (auto Case : SI.cases()) {
694 assert(Case.getCaseSuccessor() == CommonSuccBB &&(static_cast <bool> (Case.getCaseSuccessor() == CommonSuccBB
&& "Non-common successor!") ? void (0) : __assert_fail
("Case.getCaseSuccessor() == CommonSuccBB && \"Non-common successor!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 695, __extension__ __PRETTY_FUNCTION__))
695 "Non-common successor!")(static_cast <bool> (Case.getCaseSuccessor() == CommonSuccBB
&& "Non-common successor!") ? void (0) : __assert_fail
("Case.getCaseSuccessor() == CommonSuccBB && \"Non-common successor!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 695, __extension__ __PRETTY_FUNCTION__))
;
696 (void)Case;
697 if (!SkippedFirst) {
698 SkippedFirst = true;
699 continue;
700 }
701 CommonSuccBB->removePredecessor(BB,
702 /*DontDeleteUselessPHIs*/ true);
703 }
704 // Now nuke the switch and replace it with a direct branch.
705 SI.eraseFromParent();
706 BranchInst::Create(CommonSuccBB, BB);
707 } else if (DefaultExitBB) {
708 assert(SI.getNumCases() > 0 &&(static_cast <bool> (SI.getNumCases() > 0 &&
"If we had no cases we'd have a common successor!") ? void (
0) : __assert_fail ("SI.getNumCases() > 0 && \"If we had no cases we'd have a common successor!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 709, __extension__ __PRETTY_FUNCTION__))
709 "If we had no cases we'd have a common successor!")(static_cast <bool> (SI.getNumCases() > 0 &&
"If we had no cases we'd have a common successor!") ? void (
0) : __assert_fail ("SI.getNumCases() > 0 && \"If we had no cases we'd have a common successor!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 709, __extension__ __PRETTY_FUNCTION__))
;
710 // Move the last case to the default successor. This is valid as if the
711 // default got unswitched it cannot be reached. This has the advantage of
712 // being simple and keeping the number of edges from this switch to
713 // successors the same, and avoiding any PHI update complexity.
714 auto LastCaseI = std::prev(SI.case_end());
715 SI.setDefaultDest(LastCaseI->getCaseSuccessor());
716 SI.removeCase(LastCaseI);
717 }
718
719 // Walk the unswitched exit blocks and the unswitched split blocks and update
720 // the dominator tree based on the CFG edits. While we are walking unordered
721 // containers here, the API for applyUpdates takes an unordered list of
722 // updates and requires them to not contain duplicates.
723 SmallVector<DominatorTree::UpdateType, 4> DTUpdates;
724 for (auto *UnswitchedExitBB : UnswitchedExitBBs) {
725 DTUpdates.push_back({DT.Delete, ParentBB, UnswitchedExitBB});
726 DTUpdates.push_back({DT.Insert, OldPH, UnswitchedExitBB});
727 }
728 for (auto SplitUnswitchedPair : SplitExitBBMap) {
729 auto *UnswitchedBB = SplitUnswitchedPair.second;
730 DTUpdates.push_back({DT.Delete, ParentBB, UnswitchedBB});
731 DTUpdates.push_back({DT.Insert, OldPH, UnswitchedBB});
732 }
733 DT.applyUpdates(DTUpdates);
734 assert(DT.verify(DominatorTree::VerificationLevel::Fast))(static_cast <bool> (DT.verify(DominatorTree::VerificationLevel
::Fast)) ? void (0) : __assert_fail ("DT.verify(DominatorTree::VerificationLevel::Fast)"
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 734, __extension__ __PRETTY_FUNCTION__))
;
735
736 // We may have changed the nesting relationship for this loop so hoist it to
737 // its correct parent if needed.
738 hoistLoopToNewParent(L, *NewPH, DT, LI);
739
740 ++NumTrivial;
741 ++NumSwitches;
742 return true;
743}
744
745/// This routine scans the loop to find a branch or switch which occurs before
746/// any side effects occur. These can potentially be unswitched without
747/// duplicating the loop. If a branch or switch is successfully unswitched the
748/// scanning continues to see if subsequent branches or switches have become
749/// trivial. Once all trivial candidates have been unswitched, this routine
750/// returns.
751///
752/// The return value indicates whether anything was unswitched (and therefore
753/// changed).
754///
755/// If `SE` is not null, it will be updated based on the potential loop SCEVs
756/// invalidated by this.
757static bool unswitchAllTrivialConditions(Loop &L, DominatorTree &DT,
758 LoopInfo &LI, ScalarEvolution *SE) {
759 bool Changed = false;
760
761 // If loop header has only one reachable successor we should keep looking for
762 // trivial condition candidates in the successor as well. An alternative is
763 // to constant fold conditions and merge successors into loop header (then we
764 // only need to check header's terminator). The reason for not doing this in
765 // LoopUnswitch pass is that it could potentially break LoopPassManager's
766 // invariants. Folding dead branches could either eliminate the current loop
767 // or make other loops unreachable. LCSSA form might also not be preserved
768 // after deleting branches. The following code keeps traversing loop header's
769 // successors until it finds the trivial condition candidate (condition that
770 // is not a constant). Since unswitching generates branches with constant
771 // conditions, this scenario could be very common in practice.
772 BasicBlock *CurrentBB = L.getHeader();
773 SmallPtrSet<BasicBlock *, 8> Visited;
774 Visited.insert(CurrentBB);
775 do {
776 // Check if there are any side-effecting instructions (e.g. stores, calls,
777 // volatile loads) in the part of the loop that the code *would* execute
778 // without unswitching.
779 if (llvm::any_of(*CurrentBB,
780 [](Instruction &I) { return I.mayHaveSideEffects(); }))
781 return Changed;
782
783 TerminatorInst *CurrentTerm = CurrentBB->getTerminator();
784
785 if (auto *SI = dyn_cast<SwitchInst>(CurrentTerm)) {
786 // Don't bother trying to unswitch past a switch with a constant
787 // condition. This should be removed prior to running this pass by
788 // simplify-cfg.
789 if (isa<Constant>(SI->getCondition()))
790 return Changed;
791
792 if (!unswitchTrivialSwitch(L, *SI, DT, LI, SE))
793 // Couldn't unswitch this one so we're done.
794 return Changed;
795
796 // Mark that we managed to unswitch something.
797 Changed = true;
798
799 // If unswitching turned the terminator into an unconditional branch then
800 // we can continue. The unswitching logic specifically works to fold any
801 // cases it can into an unconditional branch to make it easier to
802 // recognize here.
803 auto *BI = dyn_cast<BranchInst>(CurrentBB->getTerminator());
804 if (!BI || BI->isConditional())
805 return Changed;
806
807 CurrentBB = BI->getSuccessor(0);
808 continue;
809 }
810
811 auto *BI = dyn_cast<BranchInst>(CurrentTerm);
812 if (!BI)
813 // We do not understand other terminator instructions.
814 return Changed;
815
816 // Don't bother trying to unswitch past an unconditional branch or a branch
817 // with a constant value. These should be removed by simplify-cfg prior to
818 // running this pass.
819 if (!BI->isConditional() || isa<Constant>(BI->getCondition()))
820 return Changed;
821
822 // Found a trivial condition candidate: non-foldable conditional branch. If
823 // we fail to unswitch this, we can't do anything else that is trivial.
824 if (!unswitchTrivialBranch(L, *BI, DT, LI, SE))
825 return Changed;
826
827 // Mark that we managed to unswitch something.
828 Changed = true;
829
830 // If we only unswitched some of the conditions feeding the branch, we won't
831 // have collapsed it to a single successor.
832 BI = cast<BranchInst>(CurrentBB->getTerminator());
833 if (BI->isConditional())
834 return Changed;
835
836 // Follow the newly unconditional branch into its successor.
837 CurrentBB = BI->getSuccessor(0);
838
839 // When continuing, if we exit the loop or reach a previous visited block,
840 // then we can not reach any trivial condition candidates (unfoldable
841 // branch instructions or switch instructions) and no unswitch can happen.
842 } while (L.contains(CurrentBB) && Visited.insert(CurrentBB).second);
843
844 return Changed;
845}
846
847/// Build the cloned blocks for an unswitched copy of the given loop.
848///
849/// The cloned blocks are inserted before the loop preheader (`LoopPH`) and
850/// after the split block (`SplitBB`) that will be used to select between the
851/// cloned and original loop.
852///
853/// This routine handles cloning all of the necessary loop blocks and exit
854/// blocks including rewriting their instructions and the relevant PHI nodes.
855/// Any loop blocks or exit blocks which are dominated by a different successor
856/// than the one for this clone of the loop blocks can be trivially skipped. We
857/// use the `DominatingSucc` map to determine whether a block satisfies that
858/// property with a simple map lookup.
859///
860/// It also correctly creates the unconditional branch in the cloned
861/// unswitched parent block to only point at the unswitched successor.
862///
863/// This does not handle most of the necessary updates to `LoopInfo`. Only exit
864/// block splitting is correctly reflected in `LoopInfo`, essentially all of
865/// the cloned blocks (and their loops) are left without full `LoopInfo`
866/// updates. This also doesn't fully update `DominatorTree`. It adds the cloned
867/// blocks to them but doesn't create the cloned `DominatorTree` structure and
868/// instead the caller must recompute an accurate DT. It *does* correctly
869/// update the `AssumptionCache` provided in `AC`.
870static BasicBlock *buildClonedLoopBlocks(
871 Loop &L, BasicBlock *LoopPH, BasicBlock *SplitBB,
872 ArrayRef<BasicBlock *> ExitBlocks, BasicBlock *ParentBB,
873 BasicBlock *UnswitchedSuccBB, BasicBlock *ContinueSuccBB,
874 const SmallDenseMap<BasicBlock *, BasicBlock *, 16> &DominatingSucc,
875 ValueToValueMapTy &VMap,
876 SmallVectorImpl<DominatorTree::UpdateType> &DTUpdates, AssumptionCache &AC,
877 DominatorTree &DT, LoopInfo &LI) {
878 SmallVector<BasicBlock *, 4> NewBlocks;
879 NewBlocks.reserve(L.getNumBlocks() + ExitBlocks.size());
880
881 // We will need to clone a bunch of blocks, wrap up the clone operation in
882 // a helper.
883 auto CloneBlock = [&](BasicBlock *OldBB) {
884 // Clone the basic block and insert it before the new preheader.
885 BasicBlock *NewBB = CloneBasicBlock(OldBB, VMap, ".us", OldBB->getParent());
886 NewBB->moveBefore(LoopPH);
887
888 // Record this block and the mapping.
889 NewBlocks.push_back(NewBB);
890 VMap[OldBB] = NewBB;
891
892 return NewBB;
893 };
894
895 // We skip cloning blocks when they have a dominating succ that is not the
896 // succ we are cloning for.
897 auto SkipBlock = [&](BasicBlock *BB) {
898 auto It = DominatingSucc.find(BB);
899 return It != DominatingSucc.end() && It->second != UnswitchedSuccBB;
900 };
901
902 // First, clone the preheader.
903 auto *ClonedPH = CloneBlock(LoopPH);
904
905 // Then clone all the loop blocks, skipping the ones that aren't necessary.
906 for (auto *LoopBB : L.blocks())
907 if (!SkipBlock(LoopBB))
908 CloneBlock(LoopBB);
909
910 // Split all the loop exit edges so that when we clone the exit blocks, if
911 // any of the exit blocks are *also* a preheader for some other loop, we
912 // don't create multiple predecessors entering the loop header.
913 for (auto *ExitBB : ExitBlocks) {
914 if (SkipBlock(ExitBB))
915 continue;
916
917 // When we are going to clone an exit, we don't need to clone all the
918 // instructions in the exit block and we want to ensure we have an easy
919 // place to merge the CFG, so split the exit first. This is always safe to
920 // do because there cannot be any non-loop predecessors of a loop exit in
921 // loop simplified form.
922 auto *MergeBB = SplitBlock(ExitBB, &ExitBB->front(), &DT, &LI);
923
924 // Rearrange the names to make it easier to write test cases by having the
925 // exit block carry the suffix rather than the merge block carrying the
926 // suffix.
927 MergeBB->takeName(ExitBB);
928 ExitBB->setName(Twine(MergeBB->getName()) + ".split");
929
930 // Now clone the original exit block.
931 auto *ClonedExitBB = CloneBlock(ExitBB);
932 assert(ClonedExitBB->getTerminator()->getNumSuccessors() == 1 &&(static_cast <bool> (ClonedExitBB->getTerminator()->
getNumSuccessors() == 1 && "Exit block should have been split to have one successor!"
) ? void (0) : __assert_fail ("ClonedExitBB->getTerminator()->getNumSuccessors() == 1 && \"Exit block should have been split to have one successor!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 933, __extension__ __PRETTY_FUNCTION__))
933 "Exit block should have been split to have one successor!")(static_cast <bool> (ClonedExitBB->getTerminator()->
getNumSuccessors() == 1 && "Exit block should have been split to have one successor!"
) ? void (0) : __assert_fail ("ClonedExitBB->getTerminator()->getNumSuccessors() == 1 && \"Exit block should have been split to have one successor!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 933, __extension__ __PRETTY_FUNCTION__))
;
934 assert(ClonedExitBB->getTerminator()->getSuccessor(0) == MergeBB &&(static_cast <bool> (ClonedExitBB->getTerminator()->
getSuccessor(0) == MergeBB && "Cloned exit block has the wrong successor!"
) ? void (0) : __assert_fail ("ClonedExitBB->getTerminator()->getSuccessor(0) == MergeBB && \"Cloned exit block has the wrong successor!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 935, __extension__ __PRETTY_FUNCTION__))
935 "Cloned exit block has the wrong successor!")(static_cast <bool> (ClonedExitBB->getTerminator()->
getSuccessor(0) == MergeBB && "Cloned exit block has the wrong successor!"
) ? void (0) : __assert_fail ("ClonedExitBB->getTerminator()->getSuccessor(0) == MergeBB && \"Cloned exit block has the wrong successor!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 935, __extension__ __PRETTY_FUNCTION__))
;
936
937 // Remap any cloned instructions and create a merge phi node for them.
938 for (auto ZippedInsts : llvm::zip_first(
939 llvm::make_range(ExitBB->begin(), std::prev(ExitBB->end())),
940 llvm::make_range(ClonedExitBB->begin(),
941 std::prev(ClonedExitBB->end())))) {
942 Instruction &I = std::get<0>(ZippedInsts);
943 Instruction &ClonedI = std::get<1>(ZippedInsts);
944
945 // The only instructions in the exit block should be PHI nodes and
946 // potentially a landing pad.
947 assert((static_cast <bool> ((isa<PHINode>(I) || isa<LandingPadInst
>(I) || isa<CatchPadInst>(I)) && "Bad instruction in exit block!"
) ? void (0) : __assert_fail ("(isa<PHINode>(I) || isa<LandingPadInst>(I) || isa<CatchPadInst>(I)) && \"Bad instruction in exit block!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 949, __extension__ __PRETTY_FUNCTION__))
948 (isa<PHINode>(I) || isa<LandingPadInst>(I) || isa<CatchPadInst>(I)) &&(static_cast <bool> ((isa<PHINode>(I) || isa<LandingPadInst
>(I) || isa<CatchPadInst>(I)) && "Bad instruction in exit block!"
) ? void (0) : __assert_fail ("(isa<PHINode>(I) || isa<LandingPadInst>(I) || isa<CatchPadInst>(I)) && \"Bad instruction in exit block!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 949, __extension__ __PRETTY_FUNCTION__))
949 "Bad instruction in exit block!")(static_cast <bool> ((isa<PHINode>(I) || isa<LandingPadInst
>(I) || isa<CatchPadInst>(I)) && "Bad instruction in exit block!"
) ? void (0) : __assert_fail ("(isa<PHINode>(I) || isa<LandingPadInst>(I) || isa<CatchPadInst>(I)) && \"Bad instruction in exit block!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 949, __extension__ __PRETTY_FUNCTION__))
;
950 // We should have a value map between the instruction and its clone.
951 assert(VMap.lookup(&I) == &ClonedI && "Mismatch in the value map!")(static_cast <bool> (VMap.lookup(&I) == &ClonedI
&& "Mismatch in the value map!") ? void (0) : __assert_fail
("VMap.lookup(&I) == &ClonedI && \"Mismatch in the value map!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 951, __extension__ __PRETTY_FUNCTION__))
;
952
953 auto *MergePN =
954 PHINode::Create(I.getType(), /*NumReservedValues*/ 2, ".us-phi",
955 &*MergeBB->getFirstInsertionPt());
956 I.replaceAllUsesWith(MergePN);
957 MergePN->addIncoming(&I, ExitBB);
958 MergePN->addIncoming(&ClonedI, ClonedExitBB);
959 }
960 }
961
962 // Rewrite the instructions in the cloned blocks to refer to the instructions
963 // in the cloned blocks. We have to do this as a second pass so that we have
964 // everything available. Also, we have inserted new instructions which may
965 // include assume intrinsics, so we update the assumption cache while
966 // processing this.
967 for (auto *ClonedBB : NewBlocks)
968 for (Instruction &I : *ClonedBB) {
969 RemapInstruction(&I, VMap,
970 RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
971 if (auto *II = dyn_cast<IntrinsicInst>(&I))
972 if (II->getIntrinsicID() == Intrinsic::assume)
973 AC.registerAssumption(II);
974 }
975
976 // Update any PHI nodes in the cloned successors of the skipped blocks to not
977 // have spurious incoming values.
978 for (auto *LoopBB : L.blocks())
979 if (SkipBlock(LoopBB))
980 for (auto *SuccBB : successors(LoopBB))
981 if (auto *ClonedSuccBB = cast_or_null<BasicBlock>(VMap.lookup(SuccBB)))
982 for (PHINode &PN : ClonedSuccBB->phis())
983 PN.removeIncomingValue(LoopBB, /*DeletePHIIfEmpty*/ false);
984
985 // Remove the cloned parent as a predecessor of any successor we ended up
986 // cloning other than the unswitched one.
987 auto *ClonedParentBB = cast<BasicBlock>(VMap.lookup(ParentBB));
988 for (auto *SuccBB : successors(ParentBB)) {
989 if (SuccBB == UnswitchedSuccBB)
990 continue;
991
992 auto *ClonedSuccBB = cast_or_null<BasicBlock>(VMap.lookup(SuccBB));
993 if (!ClonedSuccBB)
994 continue;
995
996 ClonedSuccBB->removePredecessor(ClonedParentBB,
997 /*DontDeleteUselessPHIs*/ true);
998 }
999
1000 // Replace the cloned branch with an unconditional branch to the cloned
1001 // unswitched successor.
1002 auto *ClonedSuccBB = cast<BasicBlock>(VMap.lookup(UnswitchedSuccBB));
1003 ClonedParentBB->getTerminator()->eraseFromParent();
1004 BranchInst::Create(ClonedSuccBB, ClonedParentBB);
1005
1006 // If there are duplicate entries in the PHI nodes because of multiple edges
1007 // to the unswitched successor, we need to nuke all but one as we replaced it
1008 // with a direct branch.
1009 for (PHINode &PN : ClonedSuccBB->phis()) {
1010 bool Found = false;
1011 // Loop over the incoming operands backwards so we can easily delete as we
1012 // go without invalidating the index.
1013 for (int i = PN.getNumOperands() - 1; i >= 0; --i) {
1014 if (PN.getIncomingBlock(i) != ClonedParentBB)
1015 continue;
1016 if (!Found) {
1017 Found = true;
1018 continue;
1019 }
1020 PN.removeIncomingValue(i, /*DeletePHIIfEmpty*/ false);
1021 }
1022 }
1023
1024 // Record the domtree updates for the new blocks.
1025 SmallPtrSet<BasicBlock *, 4> SuccSet;
1026 for (auto *ClonedBB : NewBlocks) {
1027 for (auto *SuccBB : successors(ClonedBB))
1028 if (SuccSet.insert(SuccBB).second)
1029 DTUpdates.push_back({DominatorTree::Insert, ClonedBB, SuccBB});
1030 SuccSet.clear();
1031 }
1032
1033 return ClonedPH;
1034}
1035
1036/// Recursively clone the specified loop and all of its children.
1037///
1038/// The target parent loop for the clone should be provided, or can be null if
1039/// the clone is a top-level loop. While cloning, all the blocks are mapped
1040/// with the provided value map. The entire original loop must be present in
1041/// the value map. The cloned loop is returned.
1042static Loop *cloneLoopNest(Loop &OrigRootL, Loop *RootParentL,
1043 const ValueToValueMapTy &VMap, LoopInfo &LI) {
1044 auto AddClonedBlocksToLoop = [&](Loop &OrigL, Loop &ClonedL) {
1045 assert(ClonedL.getBlocks().empty() && "Must start with an empty loop!")(static_cast <bool> (ClonedL.getBlocks().empty() &&
"Must start with an empty loop!") ? void (0) : __assert_fail
("ClonedL.getBlocks().empty() && \"Must start with an empty loop!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1045, __extension__ __PRETTY_FUNCTION__))
;
1046 ClonedL.reserveBlocks(OrigL.getNumBlocks());
1047 for (auto *BB : OrigL.blocks()) {
1048 auto *ClonedBB = cast<BasicBlock>(VMap.lookup(BB));
1049 ClonedL.addBlockEntry(ClonedBB);
1050 if (LI.getLoopFor(BB) == &OrigL)
1051 LI.changeLoopFor(ClonedBB, &ClonedL);
1052 }
1053 };
1054
1055 // We specially handle the first loop because it may get cloned into
1056 // a different parent and because we most commonly are cloning leaf loops.
1057 Loop *ClonedRootL = LI.AllocateLoop();
1058 if (RootParentL)
1059 RootParentL->addChildLoop(ClonedRootL);
1060 else
1061 LI.addTopLevelLoop(ClonedRootL);
1062 AddClonedBlocksToLoop(OrigRootL, *ClonedRootL);
1063
1064 if (OrigRootL.empty())
1065 return ClonedRootL;
1066
1067 // If we have a nest, we can quickly clone the entire loop nest using an
1068 // iterative approach because it is a tree. We keep the cloned parent in the
1069 // data structure to avoid repeatedly querying through a map to find it.
1070 SmallVector<std::pair<Loop *, Loop *>, 16> LoopsToClone;
1071 // Build up the loops to clone in reverse order as we'll clone them from the
1072 // back.
1073 for (Loop *ChildL : llvm::reverse(OrigRootL))
1074 LoopsToClone.push_back({ClonedRootL, ChildL});
1075 do {
1076 Loop *ClonedParentL, *L;
1077 std::tie(ClonedParentL, L) = LoopsToClone.pop_back_val();
1078 Loop *ClonedL = LI.AllocateLoop();
1079 ClonedParentL->addChildLoop(ClonedL);
1080 AddClonedBlocksToLoop(*L, *ClonedL);
1081 for (Loop *ChildL : llvm::reverse(*L))
1082 LoopsToClone.push_back({ClonedL, ChildL});
1083 } while (!LoopsToClone.empty());
1084
1085 return ClonedRootL;
1086}
1087
1088/// Build the cloned loops of an original loop from unswitching.
1089///
1090/// Because unswitching simplifies the CFG of the loop, this isn't a trivial
1091/// operation. We need to re-verify that there even is a loop (as the backedge
1092/// may not have been cloned), and even if there are remaining backedges the
1093/// backedge set may be different. However, we know that each child loop is
1094/// undisturbed, we only need to find where to place each child loop within
1095/// either any parent loop or within a cloned version of the original loop.
1096///
1097/// Because child loops may end up cloned outside of any cloned version of the
1098/// original loop, multiple cloned sibling loops may be created. All of them
1099/// are returned so that the newly introduced loop nest roots can be
1100/// identified.
1101static void buildClonedLoops(Loop &OrigL, ArrayRef<BasicBlock *> ExitBlocks,
1102 const ValueToValueMapTy &VMap, LoopInfo &LI,
1103 SmallVectorImpl<Loop *> &NonChildClonedLoops) {
1104 Loop *ClonedL = nullptr;
1105
1106 auto *OrigPH = OrigL.getLoopPreheader();
1107 auto *OrigHeader = OrigL.getHeader();
1108
1109 auto *ClonedPH = cast<BasicBlock>(VMap.lookup(OrigPH));
1110 auto *ClonedHeader = cast<BasicBlock>(VMap.lookup(OrigHeader));
1111
1112 // We need to know the loops of the cloned exit blocks to even compute the
1113 // accurate parent loop. If we only clone exits to some parent of the
1114 // original parent, we want to clone into that outer loop. We also keep track
1115 // of the loops that our cloned exit blocks participate in.
1116 Loop *ParentL = nullptr;
1117 SmallVector<BasicBlock *, 4> ClonedExitsInLoops;
1118 SmallDenseMap<BasicBlock *, Loop *, 16> ExitLoopMap;
1119 ClonedExitsInLoops.reserve(ExitBlocks.size());
1120 for (auto *ExitBB : ExitBlocks)
1121 if (auto *ClonedExitBB = cast_or_null<BasicBlock>(VMap.lookup(ExitBB)))
1122 if (Loop *ExitL = LI.getLoopFor(ExitBB)) {
1123 ExitLoopMap[ClonedExitBB] = ExitL;
1124 ClonedExitsInLoops.push_back(ClonedExitBB);
1125 if (!ParentL || (ParentL != ExitL && ParentL->contains(ExitL)))
1126 ParentL = ExitL;
1127 }
1128 assert((!ParentL || ParentL == OrigL.getParentLoop() ||(static_cast <bool> ((!ParentL || ParentL == OrigL.getParentLoop
() || ParentL->contains(OrigL.getParentLoop())) &&
"The computed parent loop should always contain (or be) the parent of "
"the original loop.") ? void (0) : __assert_fail ("(!ParentL || ParentL == OrigL.getParentLoop() || ParentL->contains(OrigL.getParentLoop())) && \"The computed parent loop should always contain (or be) the parent of \" \"the original loop.\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1131, __extension__ __PRETTY_FUNCTION__))
1129 ParentL->contains(OrigL.getParentLoop())) &&(static_cast <bool> ((!ParentL || ParentL == OrigL.getParentLoop
() || ParentL->contains(OrigL.getParentLoop())) &&
"The computed parent loop should always contain (or be) the parent of "
"the original loop.") ? void (0) : __assert_fail ("(!ParentL || ParentL == OrigL.getParentLoop() || ParentL->contains(OrigL.getParentLoop())) && \"The computed parent loop should always contain (or be) the parent of \" \"the original loop.\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1131, __extension__ __PRETTY_FUNCTION__))
1130 "The computed parent loop should always contain (or be) the parent of "(static_cast <bool> ((!ParentL || ParentL == OrigL.getParentLoop
() || ParentL->contains(OrigL.getParentLoop())) &&
"The computed parent loop should always contain (or be) the parent of "
"the original loop.") ? void (0) : __assert_fail ("(!ParentL || ParentL == OrigL.getParentLoop() || ParentL->contains(OrigL.getParentLoop())) && \"The computed parent loop should always contain (or be) the parent of \" \"the original loop.\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1131, __extension__ __PRETTY_FUNCTION__))
1131 "the original loop.")(static_cast <bool> ((!ParentL || ParentL == OrigL.getParentLoop
() || ParentL->contains(OrigL.getParentLoop())) &&
"The computed parent loop should always contain (or be) the parent of "
"the original loop.") ? void (0) : __assert_fail ("(!ParentL || ParentL == OrigL.getParentLoop() || ParentL->contains(OrigL.getParentLoop())) && \"The computed parent loop should always contain (or be) the parent of \" \"the original loop.\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1131, __extension__ __PRETTY_FUNCTION__))
;
1132
1133 // We build the set of blocks dominated by the cloned header from the set of
1134 // cloned blocks out of the original loop. While not all of these will
1135 // necessarily be in the cloned loop, it is enough to establish that they
1136 // aren't in unreachable cycles, etc.
1137 SmallSetVector<BasicBlock *, 16> ClonedLoopBlocks;
1138 for (auto *BB : OrigL.blocks())
1139 if (auto *ClonedBB = cast_or_null<BasicBlock>(VMap.lookup(BB)))
1140 ClonedLoopBlocks.insert(ClonedBB);
1141
1142 // Rebuild the set of blocks that will end up in the cloned loop. We may have
1143 // skipped cloning some region of this loop which can in turn skip some of
1144 // the backedges so we have to rebuild the blocks in the loop based on the
1145 // backedges that remain after cloning.
1146 SmallVector<BasicBlock *, 16> Worklist;
1147 SmallPtrSet<BasicBlock *, 16> BlocksInClonedLoop;
1148 for (auto *Pred : predecessors(ClonedHeader)) {
1149 // The only possible non-loop header predecessor is the preheader because
1150 // we know we cloned the loop in simplified form.
1151 if (Pred == ClonedPH)
1152 continue;
1153
1154 // Because the loop was in simplified form, the only non-loop predecessor
1155 // should be the preheader.
1156 assert(ClonedLoopBlocks.count(Pred) && "Found a predecessor of the loop "(static_cast <bool> (ClonedLoopBlocks.count(Pred) &&
"Found a predecessor of the loop " "header other than the preheader "
"that is not part of the loop!") ? void (0) : __assert_fail (
"ClonedLoopBlocks.count(Pred) && \"Found a predecessor of the loop \" \"header other than the preheader \" \"that is not part of the loop!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1158, __extension__ __PRETTY_FUNCTION__))
1157 "header other than the preheader "(static_cast <bool> (ClonedLoopBlocks.count(Pred) &&
"Found a predecessor of the loop " "header other than the preheader "
"that is not part of the loop!") ? void (0) : __assert_fail (
"ClonedLoopBlocks.count(Pred) && \"Found a predecessor of the loop \" \"header other than the preheader \" \"that is not part of the loop!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1158, __extension__ __PRETTY_FUNCTION__))
1158 "that is not part of the loop!")(static_cast <bool> (ClonedLoopBlocks.count(Pred) &&
"Found a predecessor of the loop " "header other than the preheader "
"that is not part of the loop!") ? void (0) : __assert_fail (
"ClonedLoopBlocks.count(Pred) && \"Found a predecessor of the loop \" \"header other than the preheader \" \"that is not part of the loop!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1158, __extension__ __PRETTY_FUNCTION__))
;
1159
1160 // Insert this block into the loop set and on the first visit (and if it
1161 // isn't the header we're currently walking) put it into the worklist to
1162 // recurse through.
1163 if (BlocksInClonedLoop.insert(Pred).second && Pred != ClonedHeader)
1164 Worklist.push_back(Pred);
1165 }
1166
1167 // If we had any backedges then there *is* a cloned loop. Put the header into
1168 // the loop set and then walk the worklist backwards to find all the blocks
1169 // that remain within the loop after cloning.
1170 if (!BlocksInClonedLoop.empty()) {
1171 BlocksInClonedLoop.insert(ClonedHeader);
1172
1173 while (!Worklist.empty()) {
1174 BasicBlock *BB = Worklist.pop_back_val();
1175 assert(BlocksInClonedLoop.count(BB) &&(static_cast <bool> (BlocksInClonedLoop.count(BB) &&
"Didn't put block into the loop set!") ? void (0) : __assert_fail
("BlocksInClonedLoop.count(BB) && \"Didn't put block into the loop set!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1176, __extension__ __PRETTY_FUNCTION__))
1176 "Didn't put block into the loop set!")(static_cast <bool> (BlocksInClonedLoop.count(BB) &&
"Didn't put block into the loop set!") ? void (0) : __assert_fail
("BlocksInClonedLoop.count(BB) && \"Didn't put block into the loop set!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1176, __extension__ __PRETTY_FUNCTION__))
;
1177
1178 // Insert any predecessors that are in the possible set into the cloned
1179 // set, and if the insert is successful, add them to the worklist. Note
1180 // that we filter on the blocks that are definitely reachable via the
1181 // backedge to the loop header so we may prune out dead code within the
1182 // cloned loop.
1183 for (auto *Pred : predecessors(BB))
1184 if (ClonedLoopBlocks.count(Pred) &&
1185 BlocksInClonedLoop.insert(Pred).second)
1186 Worklist.push_back(Pred);
1187 }
1188
1189 ClonedL = LI.AllocateLoop();
1190 if (ParentL) {
1191 ParentL->addBasicBlockToLoop(ClonedPH, LI);
1192 ParentL->addChildLoop(ClonedL);
1193 } else {
1194 LI.addTopLevelLoop(ClonedL);
1195 }
1196 NonChildClonedLoops.push_back(ClonedL);
1197
1198 ClonedL->reserveBlocks(BlocksInClonedLoop.size());
1199 // We don't want to just add the cloned loop blocks based on how we
1200 // discovered them. The original order of blocks was carefully built in
1201 // a way that doesn't rely on predecessor ordering. Rather than re-invent
1202 // that logic, we just re-walk the original blocks (and those of the child
1203 // loops) and filter them as we add them into the cloned loop.
1204 for (auto *BB : OrigL.blocks()) {
1205 auto *ClonedBB = cast_or_null<BasicBlock>(VMap.lookup(BB));
1206 if (!ClonedBB || !BlocksInClonedLoop.count(ClonedBB))
1207 continue;
1208
1209 // Directly add the blocks that are only in this loop.
1210 if (LI.getLoopFor(BB) == &OrigL) {
1211 ClonedL->addBasicBlockToLoop(ClonedBB, LI);
1212 continue;
1213 }
1214
1215 // We want to manually add it to this loop and parents.
1216 // Registering it with LoopInfo will happen when we clone the top
1217 // loop for this block.
1218 for (Loop *PL = ClonedL; PL; PL = PL->getParentLoop())
1219 PL->addBlockEntry(ClonedBB);
1220 }
1221
1222 // Now add each child loop whose header remains within the cloned loop. All
1223 // of the blocks within the loop must satisfy the same constraints as the
1224 // header so once we pass the header checks we can just clone the entire
1225 // child loop nest.
1226 for (Loop *ChildL : OrigL) {
1227 auto *ClonedChildHeader =
1228 cast_or_null<BasicBlock>(VMap.lookup(ChildL->getHeader()));
1229 if (!ClonedChildHeader || !BlocksInClonedLoop.count(ClonedChildHeader))
1230 continue;
1231
1232#ifndef NDEBUG
1233 // We should never have a cloned child loop header but fail to have
1234 // all of the blocks for that child loop.
1235 for (auto *ChildLoopBB : ChildL->blocks())
1236 assert(BlocksInClonedLoop.count((static_cast <bool> (BlocksInClonedLoop.count( cast<
BasicBlock>(VMap.lookup(ChildLoopBB))) && "Child cloned loop has a header within the cloned outer "
"loop but not all of its blocks!") ? void (0) : __assert_fail
("BlocksInClonedLoop.count( cast<BasicBlock>(VMap.lookup(ChildLoopBB))) && \"Child cloned loop has a header within the cloned outer \" \"loop but not all of its blocks!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1239, __extension__ __PRETTY_FUNCTION__))
1237 cast<BasicBlock>(VMap.lookup(ChildLoopBB))) &&(static_cast <bool> (BlocksInClonedLoop.count( cast<
BasicBlock>(VMap.lookup(ChildLoopBB))) && "Child cloned loop has a header within the cloned outer "
"loop but not all of its blocks!") ? void (0) : __assert_fail
("BlocksInClonedLoop.count( cast<BasicBlock>(VMap.lookup(ChildLoopBB))) && \"Child cloned loop has a header within the cloned outer \" \"loop but not all of its blocks!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1239, __extension__ __PRETTY_FUNCTION__))
1238 "Child cloned loop has a header within the cloned outer "(static_cast <bool> (BlocksInClonedLoop.count( cast<
BasicBlock>(VMap.lookup(ChildLoopBB))) && "Child cloned loop has a header within the cloned outer "
"loop but not all of its blocks!") ? void (0) : __assert_fail
("BlocksInClonedLoop.count( cast<BasicBlock>(VMap.lookup(ChildLoopBB))) && \"Child cloned loop has a header within the cloned outer \" \"loop but not all of its blocks!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1239, __extension__ __PRETTY_FUNCTION__))
1239 "loop but not all of its blocks!")(static_cast <bool> (BlocksInClonedLoop.count( cast<
BasicBlock>(VMap.lookup(ChildLoopBB))) && "Child cloned loop has a header within the cloned outer "
"loop but not all of its blocks!") ? void (0) : __assert_fail
("BlocksInClonedLoop.count( cast<BasicBlock>(VMap.lookup(ChildLoopBB))) && \"Child cloned loop has a header within the cloned outer \" \"loop but not all of its blocks!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1239, __extension__ __PRETTY_FUNCTION__))
;
1240#endif
1241
1242 cloneLoopNest(*ChildL, ClonedL, VMap, LI);
1243 }
1244 }
1245
1246 // Now that we've handled all the components of the original loop that were
1247 // cloned into a new loop, we still need to handle anything from the original
1248 // loop that wasn't in a cloned loop.
1249
1250 // Figure out what blocks are left to place within any loop nest containing
1251 // the unswitched loop. If we never formed a loop, the cloned PH is one of
1252 // them.
1253 SmallPtrSet<BasicBlock *, 16> UnloopedBlockSet;
1254 if (BlocksInClonedLoop.empty())
1255 UnloopedBlockSet.insert(ClonedPH);
1256 for (auto *ClonedBB : ClonedLoopBlocks)
1257 if (!BlocksInClonedLoop.count(ClonedBB))
1258 UnloopedBlockSet.insert(ClonedBB);
1259
1260 // Copy the cloned exits and sort them in ascending loop depth, we'll work
1261 // backwards across these to process them inside out. The order shouldn't
1262 // matter as we're just trying to build up the map from inside-out; we use
1263 // the map in a more stably ordered way below.
1264 auto OrderedClonedExitsInLoops = ClonedExitsInLoops;
1265 llvm::sort(OrderedClonedExitsInLoops.begin(), OrderedClonedExitsInLoops.end(),
1266 [&](BasicBlock *LHS, BasicBlock *RHS) {
1267 return ExitLoopMap.lookup(LHS)->getLoopDepth() <
1268 ExitLoopMap.lookup(RHS)->getLoopDepth();
1269 });
1270
1271 // Populate the existing ExitLoopMap with everything reachable from each
1272 // exit, starting from the inner most exit.
1273 while (!UnloopedBlockSet.empty() && !OrderedClonedExitsInLoops.empty()) {
1274 assert(Worklist.empty() && "Didn't clear worklist!")(static_cast <bool> (Worklist.empty() && "Didn't clear worklist!"
) ? void (0) : __assert_fail ("Worklist.empty() && \"Didn't clear worklist!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1274, __extension__ __PRETTY_FUNCTION__))
;
1275
1276 BasicBlock *ExitBB = OrderedClonedExitsInLoops.pop_back_val();
1277 Loop *ExitL = ExitLoopMap.lookup(ExitBB);
1278
1279 // Walk the CFG back until we hit the cloned PH adding everything reachable
1280 // and in the unlooped set to this exit block's loop.
1281 Worklist.push_back(ExitBB);
1282 do {
1283 BasicBlock *BB = Worklist.pop_back_val();
1284 // We can stop recursing at the cloned preheader (if we get there).
1285 if (BB == ClonedPH)
1286 continue;
1287
1288 for (BasicBlock *PredBB : predecessors(BB)) {
1289 // If this pred has already been moved to our set or is part of some
1290 // (inner) loop, no update needed.
1291 if (!UnloopedBlockSet.erase(PredBB)) {
1292 assert((static_cast <bool> ((BlocksInClonedLoop.count(PredBB) ||
ExitLoopMap.count(PredBB)) && "Predecessor not mapped to a loop!"
) ? void (0) : __assert_fail ("(BlocksInClonedLoop.count(PredBB) || ExitLoopMap.count(PredBB)) && \"Predecessor not mapped to a loop!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1294, __extension__ __PRETTY_FUNCTION__))
1293 (BlocksInClonedLoop.count(PredBB) || ExitLoopMap.count(PredBB)) &&(static_cast <bool> ((BlocksInClonedLoop.count(PredBB) ||
ExitLoopMap.count(PredBB)) && "Predecessor not mapped to a loop!"
) ? void (0) : __assert_fail ("(BlocksInClonedLoop.count(PredBB) || ExitLoopMap.count(PredBB)) && \"Predecessor not mapped to a loop!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1294, __extension__ __PRETTY_FUNCTION__))
1294 "Predecessor not mapped to a loop!")(static_cast <bool> ((BlocksInClonedLoop.count(PredBB) ||
ExitLoopMap.count(PredBB)) && "Predecessor not mapped to a loop!"
) ? void (0) : __assert_fail ("(BlocksInClonedLoop.count(PredBB) || ExitLoopMap.count(PredBB)) && \"Predecessor not mapped to a loop!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1294, __extension__ __PRETTY_FUNCTION__))
;
1295 continue;
1296 }
1297
1298 // We just insert into the loop set here. We'll add these blocks to the
1299 // exit loop after we build up the set in an order that doesn't rely on
1300 // predecessor order (which in turn relies on use list order).
1301 bool Inserted = ExitLoopMap.insert({PredBB, ExitL}).second;
1302 (void)Inserted;
1303 assert(Inserted && "Should only visit an unlooped block once!")(static_cast <bool> (Inserted && "Should only visit an unlooped block once!"
) ? void (0) : __assert_fail ("Inserted && \"Should only visit an unlooped block once!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1303, __extension__ __PRETTY_FUNCTION__))
;
1304
1305 // And recurse through to its predecessors.
1306 Worklist.push_back(PredBB);
1307 }
1308 } while (!Worklist.empty());
1309 }
1310
1311 // Now that the ExitLoopMap gives as mapping for all the non-looping cloned
1312 // blocks to their outer loops, walk the cloned blocks and the cloned exits
1313 // in their original order adding them to the correct loop.
1314
1315 // We need a stable insertion order. We use the order of the original loop
1316 // order and map into the correct parent loop.
1317 for (auto *BB : llvm::concat<BasicBlock *const>(
1318 makeArrayRef(ClonedPH), ClonedLoopBlocks, ClonedExitsInLoops))
1319 if (Loop *OuterL = ExitLoopMap.lookup(BB))
1320 OuterL->addBasicBlockToLoop(BB, LI);
1321
1322#ifndef NDEBUG
1323 for (auto &BBAndL : ExitLoopMap) {
1324 auto *BB = BBAndL.first;
1325 auto *OuterL = BBAndL.second;
1326 assert(LI.getLoopFor(BB) == OuterL &&(static_cast <bool> (LI.getLoopFor(BB) == OuterL &&
"Failed to put all blocks into outer loops!") ? void (0) : __assert_fail
("LI.getLoopFor(BB) == OuterL && \"Failed to put all blocks into outer loops!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1327, __extension__ __PRETTY_FUNCTION__))
1327 "Failed to put all blocks into outer loops!")(static_cast <bool> (LI.getLoopFor(BB) == OuterL &&
"Failed to put all blocks into outer loops!") ? void (0) : __assert_fail
("LI.getLoopFor(BB) == OuterL && \"Failed to put all blocks into outer loops!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1327, __extension__ __PRETTY_FUNCTION__))
;
1328 }
1329#endif
1330
1331 // Now that all the blocks are placed into the correct containing loop in the
1332 // absence of child loops, find all the potentially cloned child loops and
1333 // clone them into whatever outer loop we placed their header into.
1334 for (Loop *ChildL : OrigL) {
1335 auto *ClonedChildHeader =
1336 cast_or_null<BasicBlock>(VMap.lookup(ChildL->getHeader()));
1337 if (!ClonedChildHeader || BlocksInClonedLoop.count(ClonedChildHeader))
1338 continue;
1339
1340#ifndef NDEBUG
1341 for (auto *ChildLoopBB : ChildL->blocks())
1342 assert(VMap.count(ChildLoopBB) &&(static_cast <bool> (VMap.count(ChildLoopBB) &&
"Cloned a child loop header but not all of that loops blocks!"
) ? void (0) : __assert_fail ("VMap.count(ChildLoopBB) && \"Cloned a child loop header but not all of that loops blocks!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1343, __extension__ __PRETTY_FUNCTION__))
1343 "Cloned a child loop header but not all of that loops blocks!")(static_cast <bool> (VMap.count(ChildLoopBB) &&
"Cloned a child loop header but not all of that loops blocks!"
) ? void (0) : __assert_fail ("VMap.count(ChildLoopBB) && \"Cloned a child loop header but not all of that loops blocks!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1343, __extension__ __PRETTY_FUNCTION__))
;
1344#endif
1345
1346 NonChildClonedLoops.push_back(cloneLoopNest(
1347 *ChildL, ExitLoopMap.lookup(ClonedChildHeader), VMap, LI));
1348 }
1349}
1350
1351static void
1352deleteDeadClonedBlocks(Loop &L, ArrayRef<BasicBlock *> ExitBlocks,
1353 ArrayRef<std::unique_ptr<ValueToValueMapTy>> VMaps,
1354 DominatorTree &DT) {
1355 // Find all the dead clones, and remove them from their successors.
1356 SmallVector<BasicBlock *, 16> DeadBlocks;
1357 for (BasicBlock *BB : llvm::concat<BasicBlock *const>(L.blocks(), ExitBlocks))
1358 for (auto &VMap : VMaps)
1359 if (BasicBlock *ClonedBB = cast_or_null<BasicBlock>(VMap->lookup(BB)))
1360 if (!DT.isReachableFromEntry(ClonedBB)) {
1361 for (BasicBlock *SuccBB : successors(ClonedBB))
1362 SuccBB->removePredecessor(ClonedBB);
1363 DeadBlocks.push_back(ClonedBB);
1364 }
1365
1366 // Drop any remaining references to break cycles.
1367 for (BasicBlock *BB : DeadBlocks)
1368 BB->dropAllReferences();
1369 // Erase them from the IR.
1370 for (BasicBlock *BB : DeadBlocks)
1371 BB->eraseFromParent();
1372}
1373
1374static void
1375deleteDeadBlocksFromLoop(Loop &L,
1376 SmallVectorImpl<BasicBlock *> &ExitBlocks,
1377 DominatorTree &DT, LoopInfo &LI) {
1378 // Find all the dead blocks, and remove them from their successors.
1379 SmallVector<BasicBlock *, 16> DeadBlocks;
1380 for (BasicBlock *BB : llvm::concat<BasicBlock *const>(L.blocks(), ExitBlocks))
1381 if (!DT.isReachableFromEntry(BB)) {
1382 for (BasicBlock *SuccBB : successors(BB))
1383 SuccBB->removePredecessor(BB);
1384 DeadBlocks.push_back(BB);
1385 }
1386
1387 SmallPtrSet<BasicBlock *, 16> DeadBlockSet(DeadBlocks.begin(),
1388 DeadBlocks.end());
1389
1390 // Filter out the dead blocks from the exit blocks list so that it can be
1391 // used in the caller.
1392 llvm::erase_if(ExitBlocks,
1393 [&](BasicBlock *BB) { return DeadBlockSet.count(BB); });
1394
1395 // Walk from this loop up through its parents removing all of the dead blocks.
1396 for (Loop *ParentL = &L; ParentL; ParentL = ParentL->getParentLoop()) {
1397 for (auto *BB : DeadBlocks)
1398 ParentL->getBlocksSet().erase(BB);
1399 llvm::erase_if(ParentL->getBlocksVector(),
1400 [&](BasicBlock *BB) { return DeadBlockSet.count(BB); });
1401 }
1402
1403 // Now delete the dead child loops. This raw delete will clear them
1404 // recursively.
1405 llvm::erase_if(L.getSubLoopsVector(), [&](Loop *ChildL) {
1406 if (!DeadBlockSet.count(ChildL->getHeader()))
1407 return false;
1408
1409 assert(llvm::all_of(ChildL->blocks(),(static_cast <bool> (llvm::all_of(ChildL->blocks(), [
&](BasicBlock *ChildBB) { return DeadBlockSet.count(ChildBB
); }) && "If the child loop header is dead all blocks in the child loop must "
"be dead as well!") ? void (0) : __assert_fail ("llvm::all_of(ChildL->blocks(), [&](BasicBlock *ChildBB) { return DeadBlockSet.count(ChildBB); }) && \"If the child loop header is dead all blocks in the child loop must \" \"be dead as well!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1414, __extension__ __PRETTY_FUNCTION__))
1410 [&](BasicBlock *ChildBB) {(static_cast <bool> (llvm::all_of(ChildL->blocks(), [
&](BasicBlock *ChildBB) { return DeadBlockSet.count(ChildBB
); }) && "If the child loop header is dead all blocks in the child loop must "
"be dead as well!") ? void (0) : __assert_fail ("llvm::all_of(ChildL->blocks(), [&](BasicBlock *ChildBB) { return DeadBlockSet.count(ChildBB); }) && \"If the child loop header is dead all blocks in the child loop must \" \"be dead as well!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1414, __extension__ __PRETTY_FUNCTION__))
1411 return DeadBlockSet.count(ChildBB);(static_cast <bool> (llvm::all_of(ChildL->blocks(), [
&](BasicBlock *ChildBB) { return DeadBlockSet.count(ChildBB
); }) && "If the child loop header is dead all blocks in the child loop must "
"be dead as well!") ? void (0) : __assert_fail ("llvm::all_of(ChildL->blocks(), [&](BasicBlock *ChildBB) { return DeadBlockSet.count(ChildBB); }) && \"If the child loop header is dead all blocks in the child loop must \" \"be dead as well!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1414, __extension__ __PRETTY_FUNCTION__))
1412 }) &&(static_cast <bool> (llvm::all_of(ChildL->blocks(), [
&](BasicBlock *ChildBB) { return DeadBlockSet.count(ChildBB
); }) && "If the child loop header is dead all blocks in the child loop must "
"be dead as well!") ? void (0) : __assert_fail ("llvm::all_of(ChildL->blocks(), [&](BasicBlock *ChildBB) { return DeadBlockSet.count(ChildBB); }) && \"If the child loop header is dead all blocks in the child loop must \" \"be dead as well!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1414, __extension__ __PRETTY_FUNCTION__))
1413 "If the child loop header is dead all blocks in the child loop must "(static_cast <bool> (llvm::all_of(ChildL->blocks(), [
&](BasicBlock *ChildBB) { return DeadBlockSet.count(ChildBB
); }) && "If the child loop header is dead all blocks in the child loop must "
"be dead as well!") ? void (0) : __assert_fail ("llvm::all_of(ChildL->blocks(), [&](BasicBlock *ChildBB) { return DeadBlockSet.count(ChildBB); }) && \"If the child loop header is dead all blocks in the child loop must \" \"be dead as well!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1414, __extension__ __PRETTY_FUNCTION__))
1414 "be dead as well!")(static_cast <bool> (llvm::all_of(ChildL->blocks(), [
&](BasicBlock *ChildBB) { return DeadBlockSet.count(ChildBB
); }) && "If the child loop header is dead all blocks in the child loop must "
"be dead as well!") ? void (0) : __assert_fail ("llvm::all_of(ChildL->blocks(), [&](BasicBlock *ChildBB) { return DeadBlockSet.count(ChildBB); }) && \"If the child loop header is dead all blocks in the child loop must \" \"be dead as well!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1414, __extension__ __PRETTY_FUNCTION__))
;
1415 LI.destroy(ChildL);
1416 return true;
1417 });
1418
1419 // Remove the loop mappings for the dead blocks and drop all the references
1420 // from these blocks to others to handle cyclic references as we start
1421 // deleting the blocks themselves.
1422 for (auto *BB : DeadBlocks) {
1423 // Check that the dominator tree has already been updated.
1424 assert(!DT.getNode(BB) && "Should already have cleared domtree!")(static_cast <bool> (!DT.getNode(BB) && "Should already have cleared domtree!"
) ? void (0) : __assert_fail ("!DT.getNode(BB) && \"Should already have cleared domtree!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1424, __extension__ __PRETTY_FUNCTION__))
;
1425 LI.changeLoopFor(BB, nullptr);
1426 BB->dropAllReferences();
1427 }
1428
1429 // Actually delete the blocks now that they've been fully unhooked from the
1430 // IR.
1431 for (auto *BB : DeadBlocks)
1432 BB->eraseFromParent();
1433}
1434
1435/// Recompute the set of blocks in a loop after unswitching.
1436///
1437/// This walks from the original headers predecessors to rebuild the loop. We
1438/// take advantage of the fact that new blocks can't have been added, and so we
1439/// filter by the original loop's blocks. This also handles potentially
1440/// unreachable code that we don't want to explore but might be found examining
1441/// the predecessors of the header.
1442///
1443/// If the original loop is no longer a loop, this will return an empty set. If
1444/// it remains a loop, all the blocks within it will be added to the set
1445/// (including those blocks in inner loops).
1446static SmallPtrSet<const BasicBlock *, 16> recomputeLoopBlockSet(Loop &L,
1447 LoopInfo &LI) {
1448 SmallPtrSet<const BasicBlock *, 16> LoopBlockSet;
1449
1450 auto *PH = L.getLoopPreheader();
1451 auto *Header = L.getHeader();
1452
1453 // A worklist to use while walking backwards from the header.
1454 SmallVector<BasicBlock *, 16> Worklist;
1455
1456 // First walk the predecessors of the header to find the backedges. This will
1457 // form the basis of our walk.
1458 for (auto *Pred : predecessors(Header)) {
1459 // Skip the preheader.
1460 if (Pred == PH)
1461 continue;
1462
1463 // Because the loop was in simplified form, the only non-loop predecessor
1464 // is the preheader.
1465 assert(L.contains(Pred) && "Found a predecessor of the loop header other "(static_cast <bool> (L.contains(Pred) && "Found a predecessor of the loop header other "
"than the preheader that is not part of the " "loop!") ? void
(0) : __assert_fail ("L.contains(Pred) && \"Found a predecessor of the loop header other \" \"than the preheader that is not part of the \" \"loop!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1467, __extension__ __PRETTY_FUNCTION__))
1466 "than the preheader that is not part of the "(static_cast <bool> (L.contains(Pred) && "Found a predecessor of the loop header other "
"than the preheader that is not part of the " "loop!") ? void
(0) : __assert_fail ("L.contains(Pred) && \"Found a predecessor of the loop header other \" \"than the preheader that is not part of the \" \"loop!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1467, __extension__ __PRETTY_FUNCTION__))
1467 "loop!")(static_cast <bool> (L.contains(Pred) && "Found a predecessor of the loop header other "
"than the preheader that is not part of the " "loop!") ? void
(0) : __assert_fail ("L.contains(Pred) && \"Found a predecessor of the loop header other \" \"than the preheader that is not part of the \" \"loop!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1467, __extension__ __PRETTY_FUNCTION__))
;
1468
1469 // Insert this block into the loop set and on the first visit and, if it
1470 // isn't the header we're currently walking, put it into the worklist to
1471 // recurse through.
1472 if (LoopBlockSet.insert(Pred).second && Pred != Header)
1473 Worklist.push_back(Pred);
1474 }
1475
1476 // If no backedges were found, we're done.
1477 if (LoopBlockSet.empty())
1478 return LoopBlockSet;
1479
1480 // We found backedges, recurse through them to identify the loop blocks.
1481 while (!Worklist.empty()) {
1482 BasicBlock *BB = Worklist.pop_back_val();
1483 assert(LoopBlockSet.count(BB) && "Didn't put block into the loop set!")(static_cast <bool> (LoopBlockSet.count(BB) && "Didn't put block into the loop set!"
) ? void (0) : __assert_fail ("LoopBlockSet.count(BB) && \"Didn't put block into the loop set!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1483, __extension__ __PRETTY_FUNCTION__))
;
1484
1485 // No need to walk past the header.
1486 if (BB == Header)
1487 continue;
1488
1489 // Because we know the inner loop structure remains valid we can use the
1490 // loop structure to jump immediately across the entire nested loop.
1491 // Further, because it is in loop simplified form, we can directly jump
1492 // to its preheader afterward.
1493 if (Loop *InnerL = LI.getLoopFor(BB))
1494 if (InnerL != &L) {
1495 assert(L.contains(InnerL) &&(static_cast <bool> (L.contains(InnerL) && "Should not reach a loop *outside* this loop!"
) ? void (0) : __assert_fail ("L.contains(InnerL) && \"Should not reach a loop *outside* this loop!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1496, __extension__ __PRETTY_FUNCTION__))
1496 "Should not reach a loop *outside* this loop!")(static_cast <bool> (L.contains(InnerL) && "Should not reach a loop *outside* this loop!"
) ? void (0) : __assert_fail ("L.contains(InnerL) && \"Should not reach a loop *outside* this loop!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1496, __extension__ __PRETTY_FUNCTION__))
;
1497 // The preheader is the only possible predecessor of the loop so
1498 // insert it into the set and check whether it was already handled.
1499 auto *InnerPH = InnerL->getLoopPreheader();
1500 assert(L.contains(InnerPH) && "Cannot contain an inner loop block "(static_cast <bool> (L.contains(InnerPH) && "Cannot contain an inner loop block "
"but not contain the inner loop " "preheader!") ? void (0) :
__assert_fail ("L.contains(InnerPH) && \"Cannot contain an inner loop block \" \"but not contain the inner loop \" \"preheader!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1502, __extension__ __PRETTY_FUNCTION__))
1501 "but not contain the inner loop "(static_cast <bool> (L.contains(InnerPH) && "Cannot contain an inner loop block "
"but not contain the inner loop " "preheader!") ? void (0) :
__assert_fail ("L.contains(InnerPH) && \"Cannot contain an inner loop block \" \"but not contain the inner loop \" \"preheader!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1502, __extension__ __PRETTY_FUNCTION__))
1502 "preheader!")(static_cast <bool> (L.contains(InnerPH) && "Cannot contain an inner loop block "
"but not contain the inner loop " "preheader!") ? void (0) :
__assert_fail ("L.contains(InnerPH) && \"Cannot contain an inner loop block \" \"but not contain the inner loop \" \"preheader!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1502, __extension__ __PRETTY_FUNCTION__))
;
1503 if (!LoopBlockSet.insert(InnerPH).second)
1504 // The only way to reach the preheader is through the loop body
1505 // itself so if it has been visited the loop is already handled.
1506 continue;
1507
1508 // Insert all of the blocks (other than those already present) into
1509 // the loop set. We expect at least the block that led us to find the
1510 // inner loop to be in the block set, but we may also have other loop
1511 // blocks if they were already enqueued as predecessors of some other
1512 // outer loop block.
1513 for (auto *InnerBB : InnerL->blocks()) {
1514 if (InnerBB == BB) {
1515 assert(LoopBlockSet.count(InnerBB) &&(static_cast <bool> (LoopBlockSet.count(InnerBB) &&
"Block should already be in the set!") ? void (0) : __assert_fail
("LoopBlockSet.count(InnerBB) && \"Block should already be in the set!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1516, __extension__ __PRETTY_FUNCTION__))
1516 "Block should already be in the set!")(static_cast <bool> (LoopBlockSet.count(InnerBB) &&
"Block should already be in the set!") ? void (0) : __assert_fail
("LoopBlockSet.count(InnerBB) && \"Block should already be in the set!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1516, __extension__ __PRETTY_FUNCTION__))
;
1517 continue;
1518 }
1519
1520 LoopBlockSet.insert(InnerBB);
1521 }
1522
1523 // Add the preheader to the worklist so we will continue past the
1524 // loop body.
1525 Worklist.push_back(InnerPH);
1526 continue;
1527 }
1528
1529 // Insert any predecessors that were in the original loop into the new
1530 // set, and if the insert is successful, add them to the worklist.
1531 for (auto *Pred : predecessors(BB))
1532 if (L.contains(Pred) && LoopBlockSet.insert(Pred).second)
1533 Worklist.push_back(Pred);
1534 }
1535
1536 assert(LoopBlockSet.count(Header) && "Cannot fail to add the header!")(static_cast <bool> (LoopBlockSet.count(Header) &&
"Cannot fail to add the header!") ? void (0) : __assert_fail
("LoopBlockSet.count(Header) && \"Cannot fail to add the header!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1536, __extension__ __PRETTY_FUNCTION__))
;
1537
1538 // We've found all the blocks participating in the loop, return our completed
1539 // set.
1540 return LoopBlockSet;
1541}
1542
1543/// Rebuild a loop after unswitching removes some subset of blocks and edges.
1544///
1545/// The removal may have removed some child loops entirely but cannot have
1546/// disturbed any remaining child loops. However, they may need to be hoisted
1547/// to the parent loop (or to be top-level loops). The original loop may be
1548/// completely removed.
1549///
1550/// The sibling loops resulting from this update are returned. If the original
1551/// loop remains a valid loop, it will be the first entry in this list with all
1552/// of the newly sibling loops following it.
1553///
1554/// Returns true if the loop remains a loop after unswitching, and false if it
1555/// is no longer a loop after unswitching (and should not continue to be
1556/// referenced).
1557static bool rebuildLoopAfterUnswitch(Loop &L, ArrayRef<BasicBlock *> ExitBlocks,
1558 LoopInfo &LI,
1559 SmallVectorImpl<Loop *> &HoistedLoops) {
1560 auto *PH = L.getLoopPreheader();
1561
1562 // Compute the actual parent loop from the exit blocks. Because we may have
1563 // pruned some exits the loop may be different from the original parent.
1564 Loop *ParentL = nullptr;
1565 SmallVector<Loop *, 4> ExitLoops;
1566 SmallVector<BasicBlock *, 4> ExitsInLoops;
1567 ExitsInLoops.reserve(ExitBlocks.size());
1568 for (auto *ExitBB : ExitBlocks)
1569 if (Loop *ExitL = LI.getLoopFor(ExitBB)) {
1570 ExitLoops.push_back(ExitL);
1571 ExitsInLoops.push_back(ExitBB);
1572 if (!ParentL || (ParentL != ExitL && ParentL->contains(ExitL)))
1573 ParentL = ExitL;
1574 }
1575
1576 // Recompute the blocks participating in this loop. This may be empty if it
1577 // is no longer a loop.
1578 auto LoopBlockSet = recomputeLoopBlockSet(L, LI);
1579
1580 // If we still have a loop, we need to re-set the loop's parent as the exit
1581 // block set changing may have moved it within the loop nest. Note that this
1582 // can only happen when this loop has a parent as it can only hoist the loop
1583 // *up* the nest.
1584 if (!LoopBlockSet.empty() && L.getParentLoop() != ParentL) {
1585 // Remove this loop's (original) blocks from all of the intervening loops.
1586 for (Loop *IL = L.getParentLoop(); IL != ParentL;
1587 IL = IL->getParentLoop()) {
1588 IL->getBlocksSet().erase(PH);
1589 for (auto *BB : L.blocks())
1590 IL->getBlocksSet().erase(BB);
1591 llvm::erase_if(IL->getBlocksVector(), [&](BasicBlock *BB) {
1592 return BB == PH || L.contains(BB);
1593 });
1594 }
1595
1596 LI.changeLoopFor(PH, ParentL);
1597 L.getParentLoop()->removeChildLoop(&L);
1598 if (ParentL)
1599 ParentL->addChildLoop(&L);
1600 else
1601 LI.addTopLevelLoop(&L);
1602 }
1603
1604 // Now we update all the blocks which are no longer within the loop.
1605 auto &Blocks = L.getBlocksVector();
1606 auto BlocksSplitI =
1607 LoopBlockSet.empty()
1608 ? Blocks.begin()
1609 : std::stable_partition(
1610 Blocks.begin(), Blocks.end(),
1611 [&](BasicBlock *BB) { return LoopBlockSet.count(BB); });
1612
1613 // Before we erase the list of unlooped blocks, build a set of them.
1614 SmallPtrSet<BasicBlock *, 16> UnloopedBlocks(BlocksSplitI, Blocks.end());
1615 if (LoopBlockSet.empty())
1616 UnloopedBlocks.insert(PH);
1617
1618 // Now erase these blocks from the loop.
1619 for (auto *BB : make_range(BlocksSplitI, Blocks.end()))
1620 L.getBlocksSet().erase(BB);
1621 Blocks.erase(BlocksSplitI, Blocks.end());
1622
1623 // Sort the exits in ascending loop depth, we'll work backwards across these
1624 // to process them inside out.
1625 std::stable_sort(ExitsInLoops.begin(), ExitsInLoops.end(),
1626 [&](BasicBlock *LHS, BasicBlock *RHS) {
1627 return LI.getLoopDepth(LHS) < LI.getLoopDepth(RHS);
1628 });
1629
1630 // We'll build up a set for each exit loop.
1631 SmallPtrSet<BasicBlock *, 16> NewExitLoopBlocks;
1632 Loop *PrevExitL = L.getParentLoop(); // The deepest possible exit loop.
1633
1634 auto RemoveUnloopedBlocksFromLoop =
1635 [](Loop &L, SmallPtrSetImpl<BasicBlock *> &UnloopedBlocks) {
1636 for (auto *BB : UnloopedBlocks)
1637 L.getBlocksSet().erase(BB);
1638 llvm::erase_if(L.getBlocksVector(), [&](BasicBlock *BB) {
1639 return UnloopedBlocks.count(BB);
1640 });
1641 };
1642
1643 SmallVector<BasicBlock *, 16> Worklist;
1644 while (!UnloopedBlocks.empty() && !ExitsInLoops.empty()) {
1645 assert(Worklist.empty() && "Didn't clear worklist!")(static_cast <bool> (Worklist.empty() && "Didn't clear worklist!"
) ? void (0) : __assert_fail ("Worklist.empty() && \"Didn't clear worklist!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1645, __extension__ __PRETTY_FUNCTION__))
;
1646 assert(NewExitLoopBlocks.empty() && "Didn't clear loop set!")(static_cast <bool> (NewExitLoopBlocks.empty() &&
"Didn't clear loop set!") ? void (0) : __assert_fail ("NewExitLoopBlocks.empty() && \"Didn't clear loop set!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1646, __extension__ __PRETTY_FUNCTION__))
;
1647
1648 // Grab the next exit block, in decreasing loop depth order.
1649 BasicBlock *ExitBB = ExitsInLoops.pop_back_val();
1650 Loop &ExitL = *LI.getLoopFor(ExitBB);
1651 assert(ExitL.contains(&L) && "Exit loop must contain the inner loop!")(static_cast <bool> (ExitL.contains(&L) && "Exit loop must contain the inner loop!"
) ? void (0) : __assert_fail ("ExitL.contains(&L) && \"Exit loop must contain the inner loop!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1651, __extension__ __PRETTY_FUNCTION__))
;
1652
1653 // Erase all of the unlooped blocks from the loops between the previous
1654 // exit loop and this exit loop. This works because the ExitInLoops list is
1655 // sorted in increasing order of loop depth and thus we visit loops in
1656 // decreasing order of loop depth.
1657 for (; PrevExitL != &ExitL; PrevExitL = PrevExitL->getParentLoop())
1658 RemoveUnloopedBlocksFromLoop(*PrevExitL, UnloopedBlocks);
1659
1660 // Walk the CFG back until we hit the cloned PH adding everything reachable
1661 // and in the unlooped set to this exit block's loop.
1662 Worklist.push_back(ExitBB);
1663 do {
1664 BasicBlock *BB = Worklist.pop_back_val();
1665 // We can stop recursing at the cloned preheader (if we get there).
1666 if (BB == PH)
1667 continue;
1668
1669 for (BasicBlock *PredBB : predecessors(BB)) {
1670 // If this pred has already been moved to our set or is part of some
1671 // (inner) loop, no update needed.
1672 if (!UnloopedBlocks.erase(PredBB)) {
1673 assert((NewExitLoopBlocks.count(PredBB) ||(static_cast <bool> ((NewExitLoopBlocks.count(PredBB) ||
ExitL.contains(LI.getLoopFor(PredBB))) && "Predecessor not in a nested loop (or already visited)!"
) ? void (0) : __assert_fail ("(NewExitLoopBlocks.count(PredBB) || ExitL.contains(LI.getLoopFor(PredBB))) && \"Predecessor not in a nested loop (or already visited)!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1675, __extension__ __PRETTY_FUNCTION__))
1674 ExitL.contains(LI.getLoopFor(PredBB))) &&(static_cast <bool> ((NewExitLoopBlocks.count(PredBB) ||
ExitL.contains(LI.getLoopFor(PredBB))) && "Predecessor not in a nested loop (or already visited)!"
) ? void (0) : __assert_fail ("(NewExitLoopBlocks.count(PredBB) || ExitL.contains(LI.getLoopFor(PredBB))) && \"Predecessor not in a nested loop (or already visited)!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1675, __extension__ __PRETTY_FUNCTION__))
1675 "Predecessor not in a nested loop (or already visited)!")(static_cast <bool> ((NewExitLoopBlocks.count(PredBB) ||
ExitL.contains(LI.getLoopFor(PredBB))) && "Predecessor not in a nested loop (or already visited)!"
) ? void (0) : __assert_fail ("(NewExitLoopBlocks.count(PredBB) || ExitL.contains(LI.getLoopFor(PredBB))) && \"Predecessor not in a nested loop (or already visited)!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1675, __extension__ __PRETTY_FUNCTION__))
;
1676 continue;
1677 }
1678
1679 // We just insert into the loop set here. We'll add these blocks to the
1680 // exit loop after we build up the set in a deterministic order rather
1681 // than the predecessor-influenced visit order.
1682 bool Inserted = NewExitLoopBlocks.insert(PredBB).second;
1683 (void)Inserted;
1684 assert(Inserted && "Should only visit an unlooped block once!")(static_cast <bool> (Inserted && "Should only visit an unlooped block once!"
) ? void (0) : __assert_fail ("Inserted && \"Should only visit an unlooped block once!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1684, __extension__ __PRETTY_FUNCTION__))
;
1685
1686 // And recurse through to its predecessors.
1687 Worklist.push_back(PredBB);
1688 }
1689 } while (!Worklist.empty());
1690
1691 // If blocks in this exit loop were directly part of the original loop (as
1692 // opposed to a child loop) update the map to point to this exit loop. This
1693 // just updates a map and so the fact that the order is unstable is fine.
1694 for (auto *BB : NewExitLoopBlocks)
1695 if (Loop *BBL = LI.getLoopFor(BB))
1696 if (BBL == &L || !L.contains(BBL))
1697 LI.changeLoopFor(BB, &ExitL);
1698
1699 // We will remove the remaining unlooped blocks from this loop in the next
1700 // iteration or below.
1701 NewExitLoopBlocks.clear();
1702 }
1703
1704 // Any remaining unlooped blocks are no longer part of any loop unless they
1705 // are part of some child loop.
1706 for (; PrevExitL; PrevExitL = PrevExitL->getParentLoop())
1707 RemoveUnloopedBlocksFromLoop(*PrevExitL, UnloopedBlocks);
1708 for (auto *BB : UnloopedBlocks)
1709 if (Loop *BBL = LI.getLoopFor(BB))
1710 if (BBL == &L || !L.contains(BBL))
1711 LI.changeLoopFor(BB, nullptr);
1712
1713 // Sink all the child loops whose headers are no longer in the loop set to
1714 // the parent (or to be top level loops). We reach into the loop and directly
1715 // update its subloop vector to make this batch update efficient.
1716 auto &SubLoops = L.getSubLoopsVector();
1717 auto SubLoopsSplitI =
1718 LoopBlockSet.empty()
1719 ? SubLoops.begin()
1720 : std::stable_partition(
1721 SubLoops.begin(), SubLoops.end(), [&](Loop *SubL) {
1722 return LoopBlockSet.count(SubL->getHeader());
1723 });
1724 for (auto *HoistedL : make_range(SubLoopsSplitI, SubLoops.end())) {
1725 HoistedLoops.push_back(HoistedL);
1726 HoistedL->setParentLoop(nullptr);
1727
1728 // To compute the new parent of this hoisted loop we look at where we
1729 // placed the preheader above. We can't lookup the header itself because we
1730 // retained the mapping from the header to the hoisted loop. But the
1731 // preheader and header should have the exact same new parent computed
1732 // based on the set of exit blocks from the original loop as the preheader
1733 // is a predecessor of the header and so reached in the reverse walk. And
1734 // because the loops were all in simplified form the preheader of the
1735 // hoisted loop can't be part of some *other* loop.
1736 if (auto *NewParentL = LI.getLoopFor(HoistedL->getLoopPreheader()))
1737 NewParentL->addChildLoop(HoistedL);
1738 else
1739 LI.addTopLevelLoop(HoistedL);
1740 }
1741 SubLoops.erase(SubLoopsSplitI, SubLoops.end());
1742
1743 // Actually delete the loop if nothing remained within it.
1744 if (Blocks.empty()) {
1745 assert(SubLoops.empty() &&(static_cast <bool> (SubLoops.empty() && "Failed to remove all subloops from the original loop!"
) ? void (0) : __assert_fail ("SubLoops.empty() && \"Failed to remove all subloops from the original loop!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1746, __extension__ __PRETTY_FUNCTION__))
1746 "Failed to remove all subloops from the original loop!")(static_cast <bool> (SubLoops.empty() && "Failed to remove all subloops from the original loop!"
) ? void (0) : __assert_fail ("SubLoops.empty() && \"Failed to remove all subloops from the original loop!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1746, __extension__ __PRETTY_FUNCTION__))
;
1747 if (Loop *ParentL = L.getParentLoop())
1748 ParentL->removeChildLoop(llvm::find(*ParentL, &L));
1749 else
1750 LI.removeLoop(llvm::find(LI, &L));
1751 LI.destroy(&L);
1752 return false;
1753 }
1754
1755 return true;
1756}
1757
1758/// Helper to visit a dominator subtree, invoking a callable on each node.
1759///
1760/// Returning false at any point will stop walking past that node of the tree.
1761template <typename CallableT>
1762void visitDomSubTree(DominatorTree &DT, BasicBlock *BB, CallableT Callable) {
1763 SmallVector<DomTreeNode *, 4> DomWorklist;
1764 DomWorklist.push_back(DT[BB]);
1765#ifndef NDEBUG
1766 SmallPtrSet<DomTreeNode *, 4> Visited;
1767 Visited.insert(DT[BB]);
1768#endif
1769 do {
1770 DomTreeNode *N = DomWorklist.pop_back_val();
1771
1772 // Visit this node.
1773 if (!Callable(N->getBlock()))
1774 continue;
1775
1776 // Accumulate the child nodes.
1777 for (DomTreeNode *ChildN : *N) {
1778 assert(Visited.insert(ChildN).second &&(static_cast <bool> (Visited.insert(ChildN).second &&
"Cannot visit a node twice when walking a tree!") ? void (0)
: __assert_fail ("Visited.insert(ChildN).second && \"Cannot visit a node twice when walking a tree!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1779, __extension__ __PRETTY_FUNCTION__))
1779 "Cannot visit a node twice when walking a tree!")(static_cast <bool> (Visited.insert(ChildN).second &&
"Cannot visit a node twice when walking a tree!") ? void (0)
: __assert_fail ("Visited.insert(ChildN).second && \"Cannot visit a node twice when walking a tree!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1779, __extension__ __PRETTY_FUNCTION__))
;
1780 DomWorklist.push_back(ChildN);
1781 }
1782 } while (!DomWorklist.empty());
1783}
1784
1785static bool unswitchNontrivialInvariants(
1786 Loop &L, TerminatorInst &TI, ArrayRef<Value *> Invariants,
1787 DominatorTree &DT, LoopInfo &LI, AssumptionCache &AC,
1788 function_ref<void(bool, ArrayRef<Loop *>)> UnswitchCB,
1789 ScalarEvolution *SE) {
1790 auto *ParentBB = TI.getParent();
1791 BranchInst *BI = dyn_cast<BranchInst>(&TI);
1792 SwitchInst *SI = BI ? nullptr : cast<SwitchInst>(&TI);
1793
1794 // We can only unswitch switches, conditional branches with an invariant
1795 // condition, or combining invariant conditions with an instruction.
1796 assert((SI || BI->isConditional()) &&(static_cast <bool> ((SI || BI->isConditional()) &&
"Can only unswitch switches and conditional branch!") ? void
(0) : __assert_fail ("(SI || BI->isConditional()) && \"Can only unswitch switches and conditional branch!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1797, __extension__ __PRETTY_FUNCTION__))
1797 "Can only unswitch switches and conditional branch!")(static_cast <bool> ((SI || BI->isConditional()) &&
"Can only unswitch switches and conditional branch!") ? void
(0) : __assert_fail ("(SI || BI->isConditional()) && \"Can only unswitch switches and conditional branch!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1797, __extension__ __PRETTY_FUNCTION__))
;
1798 bool FullUnswitch = SI || BI->getCondition() == Invariants[0];
1799 if (FullUnswitch)
1800 assert(Invariants.size() == 1 &&(static_cast <bool> (Invariants.size() == 1 && "Cannot have other invariants with full unswitching!"
) ? void (0) : __assert_fail ("Invariants.size() == 1 && \"Cannot have other invariants with full unswitching!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1801, __extension__ __PRETTY_FUNCTION__))
1801 "Cannot have other invariants with full unswitching!")(static_cast <bool> (Invariants.size() == 1 && "Cannot have other invariants with full unswitching!"
) ? void (0) : __assert_fail ("Invariants.size() == 1 && \"Cannot have other invariants with full unswitching!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1801, __extension__ __PRETTY_FUNCTION__))
;
1802 else
1803 assert(isa<Instruction>(BI->getCondition()) &&(static_cast <bool> (isa<Instruction>(BI->getCondition
()) && "Partial unswitching requires an instruction as the condition!"
) ? void (0) : __assert_fail ("isa<Instruction>(BI->getCondition()) && \"Partial unswitching requires an instruction as the condition!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1804, __extension__ __PRETTY_FUNCTION__))
1804 "Partial unswitching requires an instruction as the condition!")(static_cast <bool> (isa<Instruction>(BI->getCondition
()) && "Partial unswitching requires an instruction as the condition!"
) ? void (0) : __assert_fail ("isa<Instruction>(BI->getCondition()) && \"Partial unswitching requires an instruction as the condition!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1804, __extension__ __PRETTY_FUNCTION__))
;
1805
1806 // Constant and BBs tracking the cloned and continuing successor. When we are
1807 // unswitching the entire condition, this can just be trivially chosen to
1808 // unswitch towards `true`. However, when we are unswitching a set of
1809 // invariants combined with `and` or `or`, the combining operation determines
1810 // the best direction to unswitch: we want to unswitch the direction that will
1811 // collapse the branch.
1812 bool Direction = true;
1813 int ClonedSucc = 0;
1814 if (!FullUnswitch) {
1815 if (cast<Instruction>(BI->getCondition())->getOpcode() != Instruction::Or) {
1816 assert(cast<Instruction>(BI->getCondition())->getOpcode() ==(static_cast <bool> (cast<Instruction>(BI->getCondition
())->getOpcode() == Instruction::And && "Only `or` and `and` instructions can combine invariants being "
"unswitched.") ? void (0) : __assert_fail ("cast<Instruction>(BI->getCondition())->getOpcode() == Instruction::And && \"Only `or` and `and` instructions can combine invariants being \" \"unswitched.\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1819, __extension__ __PRETTY_FUNCTION__))
1817 Instruction::And &&(static_cast <bool> (cast<Instruction>(BI->getCondition
())->getOpcode() == Instruction::And && "Only `or` and `and` instructions can combine invariants being "
"unswitched.") ? void (0) : __assert_fail ("cast<Instruction>(BI->getCondition())->getOpcode() == Instruction::And && \"Only `or` and `and` instructions can combine invariants being \" \"unswitched.\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1819, __extension__ __PRETTY_FUNCTION__))
1818 "Only `or` and `and` instructions can combine invariants being "(static_cast <bool> (cast<Instruction>(BI->getCondition
())->getOpcode() == Instruction::And && "Only `or` and `and` instructions can combine invariants being "
"unswitched.") ? void (0) : __assert_fail ("cast<Instruction>(BI->getCondition())->getOpcode() == Instruction::And && \"Only `or` and `and` instructions can combine invariants being \" \"unswitched.\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1819, __extension__ __PRETTY_FUNCTION__))
1819 "unswitched.")(static_cast <bool> (cast<Instruction>(BI->getCondition
())->getOpcode() == Instruction::And && "Only `or` and `and` instructions can combine invariants being "
"unswitched.") ? void (0) : __assert_fail ("cast<Instruction>(BI->getCondition())->getOpcode() == Instruction::And && \"Only `or` and `and` instructions can combine invariants being \" \"unswitched.\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1819, __extension__ __PRETTY_FUNCTION__))
;
1820 Direction = false;
1821 ClonedSucc = 1;
1822 }
1823 }
1824
1825 BasicBlock *RetainedSuccBB =
1826 BI ? BI->getSuccessor(1 - ClonedSucc) : SI->getDefaultDest();
1827 SmallSetVector<BasicBlock *, 4> UnswitchedSuccBBs;
1828 if (BI)
1829 UnswitchedSuccBBs.insert(BI->getSuccessor(ClonedSucc));
1830 else
1831 for (auto Case : SI->cases())
1832 if (Case.getCaseSuccessor() != RetainedSuccBB)
1833 UnswitchedSuccBBs.insert(Case.getCaseSuccessor());
1834
1835 assert(!UnswitchedSuccBBs.count(RetainedSuccBB) &&(static_cast <bool> (!UnswitchedSuccBBs.count(RetainedSuccBB
) && "Should not unswitch the same successor we are retaining!"
) ? void (0) : __assert_fail ("!UnswitchedSuccBBs.count(RetainedSuccBB) && \"Should not unswitch the same successor we are retaining!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1836, __extension__ __PRETTY_FUNCTION__))
1836 "Should not unswitch the same successor we are retaining!")(static_cast <bool> (!UnswitchedSuccBBs.count(RetainedSuccBB
) && "Should not unswitch the same successor we are retaining!"
) ? void (0) : __assert_fail ("!UnswitchedSuccBBs.count(RetainedSuccBB) && \"Should not unswitch the same successor we are retaining!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1836, __extension__ __PRETTY_FUNCTION__))
;
1837
1838 // The branch should be in this exact loop. Any inner loop's invariant branch
1839 // should be handled by unswitching that inner loop. The caller of this
1840 // routine should filter out any candidates that remain (but were skipped for
1841 // whatever reason).
1842 assert(LI.getLoopFor(ParentBB) == &L && "Branch in an inner loop!")(static_cast <bool> (LI.getLoopFor(ParentBB) == &L &&
"Branch in an inner loop!") ? void (0) : __assert_fail ("LI.getLoopFor(ParentBB) == &L && \"Branch in an inner loop!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1842, __extension__ __PRETTY_FUNCTION__))
;
1843
1844 SmallVector<BasicBlock *, 4> ExitBlocks;
1845 L.getUniqueExitBlocks(ExitBlocks);
1846
1847 // We cannot unswitch if exit blocks contain a cleanuppad instruction as we
1848 // don't know how to split those exit blocks.
1849 // FIXME: We should teach SplitBlock to handle this and remove this
1850 // restriction.
1851 for (auto *ExitBB : ExitBlocks)
1852 if (isa<CleanupPadInst>(ExitBB->getFirstNonPHI()))
1853 return false;
1854
1855 // Compute the parent loop now before we start hacking on things.
1856 Loop *ParentL = L.getParentLoop();
1857
1858 // Compute the outer-most loop containing one of our exit blocks. This is the
1859 // furthest up our loopnest which can be mutated, which we will use below to
1860 // update things.
1861 Loop *OuterExitL = &L;
1862 for (auto *ExitBB : ExitBlocks) {
1863 Loop *NewOuterExitL = LI.getLoopFor(ExitBB);
1864 if (!NewOuterExitL) {
1865 // We exited the entire nest with this block, so we're done.
1866 OuterExitL = nullptr;
1867 break;
1868 }
1869 if (NewOuterExitL != OuterExitL && NewOuterExitL->contains(OuterExitL))
1870 OuterExitL = NewOuterExitL;
1871 }
1872
1873 // At this point, we're definitely going to unswitch something so invalidate
1874 // any cached information in ScalarEvolution for the outer most loop
1875 // containing an exit block and all nested loops.
1876 if (SE) {
1877 if (OuterExitL)
1878 SE->forgetLoop(OuterExitL);
1879 else
1880 SE->forgetTopmostLoop(&L);
1881 }
1882
1883 // If the edge from this terminator to a successor dominates that successor,
1884 // store a map from each block in its dominator subtree to it. This lets us
1885 // tell when cloning for a particular successor if a block is dominated by
1886 // some *other* successor with a single data structure. We use this to
1887 // significantly reduce cloning.
1888 SmallDenseMap<BasicBlock *, BasicBlock *, 16> DominatingSucc;
1889 for (auto *SuccBB : llvm::concat<BasicBlock *const>(
1890 makeArrayRef(RetainedSuccBB), UnswitchedSuccBBs))
1891 if (SuccBB->getUniquePredecessor() ||
1892 llvm::all_of(predecessors(SuccBB), [&](BasicBlock *PredBB) {
1893 return PredBB == ParentBB || DT.dominates(SuccBB, PredBB);
1894 }))
1895 visitDomSubTree(DT, SuccBB, [&](BasicBlock *BB) {
1896 DominatingSucc[BB] = SuccBB;
1897 return true;
1898 });
1899
1900 // Split the preheader, so that we know that there is a safe place to insert
1901 // the conditional branch. We will change the preheader to have a conditional
1902 // branch on LoopCond. The original preheader will become the split point
1903 // between the unswitched versions, and we will have a new preheader for the
1904 // original loop.
1905 BasicBlock *SplitBB = L.getLoopPreheader();
1906 BasicBlock *LoopPH = SplitEdge(SplitBB, L.getHeader(), &DT, &LI);
1907
1908 // Keep track of the dominator tree updates needed.
1909 SmallVector<DominatorTree::UpdateType, 4> DTUpdates;
1910
1911 // Clone the loop for each unswitched successor.
1912 SmallVector<std::unique_ptr<ValueToValueMapTy>, 4> VMaps;
1913 VMaps.reserve(UnswitchedSuccBBs.size());
1914 SmallDenseMap<BasicBlock *, BasicBlock *, 4> ClonedPHs;
1915 for (auto *SuccBB : UnswitchedSuccBBs) {
1916 VMaps.emplace_back(new ValueToValueMapTy());
1917 ClonedPHs[SuccBB] = buildClonedLoopBlocks(
1918 L, LoopPH, SplitBB, ExitBlocks, ParentBB, SuccBB, RetainedSuccBB,
1919 DominatingSucc, *VMaps.back(), DTUpdates, AC, DT, LI);
1920 }
1921
1922 // The stitching of the branched code back together depends on whether we're
1923 // doing full unswitching or not with the exception that we always want to
1924 // nuke the initial terminator placed in the split block.
1925 SplitBB->getTerminator()->eraseFromParent();
1926 if (FullUnswitch) {
1927 // First we need to unhook the successor relationship as we'll be replacing
1928 // the terminator with a direct branch. This is much simpler for branches
1929 // than switches so we handle those first.
1930 if (BI) {
1931 // Remove the parent as a predecessor of the unswitched successor.
1932 assert(UnswitchedSuccBBs.size() == 1 &&(static_cast <bool> (UnswitchedSuccBBs.size() == 1 &&
"Only one possible unswitched block for a branch!") ? void (
0) : __assert_fail ("UnswitchedSuccBBs.size() == 1 && \"Only one possible unswitched block for a branch!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1933, __extension__ __PRETTY_FUNCTION__))
1933 "Only one possible unswitched block for a branch!")(static_cast <bool> (UnswitchedSuccBBs.size() == 1 &&
"Only one possible unswitched block for a branch!") ? void (
0) : __assert_fail ("UnswitchedSuccBBs.size() == 1 && \"Only one possible unswitched block for a branch!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1933, __extension__ __PRETTY_FUNCTION__))
;
1934 BasicBlock *UnswitchedSuccBB = *UnswitchedSuccBBs.begin();
1935 UnswitchedSuccBB->removePredecessor(ParentBB,
1936 /*DontDeleteUselessPHIs*/ true);
1937 DTUpdates.push_back({DominatorTree::Delete, ParentBB, UnswitchedSuccBB});
1938 } else {
1939 // Note that we actually want to remove the parent block as a predecessor
1940 // of *every* case successor. The case successor is either unswitched,
1941 // completely eliminating an edge from the parent to that successor, or it
1942 // is a duplicate edge to the retained successor as the retained successor
1943 // is always the default successor and as we'll replace this with a direct
1944 // branch we no longer need the duplicate entries in the PHI nodes.
1945 assert(SI->getDefaultDest() == RetainedSuccBB &&(static_cast <bool> (SI->getDefaultDest() == RetainedSuccBB
&& "Not retaining default successor!") ? void (0) : __assert_fail
("SI->getDefaultDest() == RetainedSuccBB && \"Not retaining default successor!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1946, __extension__ __PRETTY_FUNCTION__))
1946 "Not retaining default successor!")(static_cast <bool> (SI->getDefaultDest() == RetainedSuccBB
&& "Not retaining default successor!") ? void (0) : __assert_fail
("SI->getDefaultDest() == RetainedSuccBB && \"Not retaining default successor!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1946, __extension__ __PRETTY_FUNCTION__))
;
1947 for (auto &Case : SI->cases())
1948 Case.getCaseSuccessor()->removePredecessor(
1949 ParentBB,
1950 /*DontDeleteUselessPHIs*/ true);
1951
1952 // We need to use the set to populate domtree updates as even when there
1953 // are multiple cases pointing at the same successor we only want to
1954 // remove and insert one edge in the domtree.
1955 for (BasicBlock *SuccBB : UnswitchedSuccBBs)
1956 DTUpdates.push_back({DominatorTree::Delete, ParentBB, SuccBB});
1957 }
1958
1959 // Now that we've unhooked the successor relationship, splice the terminator
1960 // from the original loop to the split.
1961 SplitBB->getInstList().splice(SplitBB->end(), ParentBB->getInstList(), TI);
1962
1963 // Now wire up the terminator to the preheaders.
1964 if (BI) {
1965 BasicBlock *ClonedPH = ClonedPHs.begin()->second;
1966 BI->setSuccessor(ClonedSucc, ClonedPH);
1967 BI->setSuccessor(1 - ClonedSucc, LoopPH);
1968 DTUpdates.push_back({DominatorTree::Insert, SplitBB, ClonedPH});
1969 } else {
1970 assert(SI && "Must either be a branch or switch!")(static_cast <bool> (SI && "Must either be a branch or switch!"
) ? void (0) : __assert_fail ("SI && \"Must either be a branch or switch!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1970, __extension__ __PRETTY_FUNCTION__))
;
1971
1972 // Walk the cases and directly update their successors.
1973 SI->setDefaultDest(LoopPH);
1974 for (auto &Case : SI->cases())
1975 if (Case.getCaseSuccessor() == RetainedSuccBB)
1976 Case.setSuccessor(LoopPH);
1977 else
1978 Case.setSuccessor(ClonedPHs.find(Case.getCaseSuccessor())->second);
1979
1980 // We need to use the set to populate domtree updates as even when there
1981 // are multiple cases pointing at the same successor we only want to
1982 // remove and insert one edge in the domtree.
1983 for (BasicBlock *SuccBB : UnswitchedSuccBBs)
1984 DTUpdates.push_back(
1985 {DominatorTree::Insert, SplitBB, ClonedPHs.find(SuccBB)->second});
1986 }
1987
1988 // Create a new unconditional branch to the continuing block (as opposed to
1989 // the one cloned).
1990 BranchInst::Create(RetainedSuccBB, ParentBB);
1991 } else {
1992 assert(BI && "Only branches have partial unswitching.")(static_cast <bool> (BI && "Only branches have partial unswitching."
) ? void (0) : __assert_fail ("BI && \"Only branches have partial unswitching.\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1992, __extension__ __PRETTY_FUNCTION__))
;
1993 assert(UnswitchedSuccBBs.size() == 1 &&(static_cast <bool> (UnswitchedSuccBBs.size() == 1 &&
"Only one possible unswitched block for a branch!") ? void (
0) : __assert_fail ("UnswitchedSuccBBs.size() == 1 && \"Only one possible unswitched block for a branch!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1994, __extension__ __PRETTY_FUNCTION__))
1994 "Only one possible unswitched block for a branch!")(static_cast <bool> (UnswitchedSuccBBs.size() == 1 &&
"Only one possible unswitched block for a branch!") ? void (
0) : __assert_fail ("UnswitchedSuccBBs.size() == 1 && \"Only one possible unswitched block for a branch!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 1994, __extension__ __PRETTY_FUNCTION__))
;
1995 BasicBlock *ClonedPH = ClonedPHs.begin()->second;
1996 // When doing a partial unswitch, we have to do a bit more work to build up
1997 // the branch in the split block.
1998 buildPartialUnswitchConditionalBranch(*SplitBB, Invariants, Direction,
1999 *ClonedPH, *LoopPH);
2000 DTUpdates.push_back({DominatorTree::Insert, SplitBB, ClonedPH});
2001 }
2002
2003 // Apply the updates accumulated above to get an up-to-date dominator tree.
2004 DT.applyUpdates(DTUpdates);
2005
2006 // Now that we have an accurate dominator tree, first delete the dead cloned
2007 // blocks so that we can accurately build any cloned loops. It is important to
2008 // not delete the blocks from the original loop yet because we still want to
2009 // reference the original loop to understand the cloned loop's structure.
2010 deleteDeadClonedBlocks(L, ExitBlocks, VMaps, DT);
2011
2012 // Build the cloned loop structure itself. This may be substantially
2013 // different from the original structure due to the simplified CFG. This also
2014 // handles inserting all the cloned blocks into the correct loops.
2015 SmallVector<Loop *, 4> NonChildClonedLoops;
2016 for (std::unique_ptr<ValueToValueMapTy> &VMap : VMaps)
2017 buildClonedLoops(L, ExitBlocks, *VMap, LI, NonChildClonedLoops);
2018
2019 // Now that our cloned loops have been built, we can update the original loop.
2020 // First we delete the dead blocks from it and then we rebuild the loop
2021 // structure taking these deletions into account.
2022 deleteDeadBlocksFromLoop(L, ExitBlocks, DT, LI);
2023 SmallVector<Loop *, 4> HoistedLoops;
2024 bool IsStillLoop = rebuildLoopAfterUnswitch(L, ExitBlocks, LI, HoistedLoops);
2025
2026 // This transformation has a high risk of corrupting the dominator tree, and
2027 // the below steps to rebuild loop structures will result in hard to debug
2028 // errors in that case so verify that the dominator tree is sane first.
2029 // FIXME: Remove this when the bugs stop showing up and rely on existing
2030 // verification steps.
2031 assert(DT.verify(DominatorTree::VerificationLevel::Fast))(static_cast <bool> (DT.verify(DominatorTree::VerificationLevel
::Fast)) ? void (0) : __assert_fail ("DT.verify(DominatorTree::VerificationLevel::Fast)"
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2031, __extension__ __PRETTY_FUNCTION__))
;
2032
2033 if (BI) {
2034 // If we unswitched a branch which collapses the condition to a known
2035 // constant we want to replace all the uses of the invariants within both
2036 // the original and cloned blocks. We do this here so that we can use the
2037 // now updated dominator tree to identify which side the users are on.
2038 assert(UnswitchedSuccBBs.size() == 1 &&(static_cast <bool> (UnswitchedSuccBBs.size() == 1 &&
"Only one possible unswitched block for a branch!") ? void (
0) : __assert_fail ("UnswitchedSuccBBs.size() == 1 && \"Only one possible unswitched block for a branch!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2039, __extension__ __PRETTY_FUNCTION__))
2039 "Only one possible unswitched block for a branch!")(static_cast <bool> (UnswitchedSuccBBs.size() == 1 &&
"Only one possible unswitched block for a branch!") ? void (
0) : __assert_fail ("UnswitchedSuccBBs.size() == 1 && \"Only one possible unswitched block for a branch!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2039, __extension__ __PRETTY_FUNCTION__))
;
2040 BasicBlock *ClonedPH = ClonedPHs.begin()->second;
2041 ConstantInt *UnswitchedReplacement =
2042 Direction ? ConstantInt::getTrue(BI->getContext())
2043 : ConstantInt::getFalse(BI->getContext());
2044 ConstantInt *ContinueReplacement =
2045 Direction ? ConstantInt::getFalse(BI->getContext())
2046 : ConstantInt::getTrue(BI->getContext());
2047 for (Value *Invariant : Invariants)
2048 for (auto UI = Invariant->use_begin(), UE = Invariant->use_end();
2049 UI != UE;) {
2050 // Grab the use and walk past it so we can clobber it in the use list.
2051 Use *U = &*UI++;
2052 Instruction *UserI = dyn_cast<Instruction>(U->getUser());
2053 if (!UserI)
2054 continue;
2055
2056 // Replace it with the 'continue' side if in the main loop body, and the
2057 // unswitched if in the cloned blocks.
2058 if (DT.dominates(LoopPH, UserI->getParent()))
2059 U->set(ContinueReplacement);
2060 else if (DT.dominates(ClonedPH, UserI->getParent()))
2061 U->set(UnswitchedReplacement);
2062 }
2063 }
2064
2065 // We can change which blocks are exit blocks of all the cloned sibling
2066 // loops, the current loop, and any parent loops which shared exit blocks
2067 // with the current loop. As a consequence, we need to re-form LCSSA for
2068 // them. But we shouldn't need to re-form LCSSA for any child loops.
2069 // FIXME: This could be made more efficient by tracking which exit blocks are
2070 // new, and focusing on them, but that isn't likely to be necessary.
2071 //
2072 // In order to reasonably rebuild LCSSA we need to walk inside-out across the
2073 // loop nest and update every loop that could have had its exits changed. We
2074 // also need to cover any intervening loops. We add all of these loops to
2075 // a list and sort them by loop depth to achieve this without updating
2076 // unnecessary loops.
2077 auto UpdateLoop = [&](Loop &UpdateL) {
2078#ifndef NDEBUG
2079 UpdateL.verifyLoop();
2080 for (Loop *ChildL : UpdateL) {
2081 ChildL->verifyLoop();
2082 assert(ChildL->isRecursivelyLCSSAForm(DT, LI) &&(static_cast <bool> (ChildL->isRecursivelyLCSSAForm(
DT, LI) && "Perturbed a child loop's LCSSA form!") ? void
(0) : __assert_fail ("ChildL->isRecursivelyLCSSAForm(DT, LI) && \"Perturbed a child loop's LCSSA form!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2083, __extension__ __PRETTY_FUNCTION__))
2083 "Perturbed a child loop's LCSSA form!")(static_cast <bool> (ChildL->isRecursivelyLCSSAForm(
DT, LI) && "Perturbed a child loop's LCSSA form!") ? void
(0) : __assert_fail ("ChildL->isRecursivelyLCSSAForm(DT, LI) && \"Perturbed a child loop's LCSSA form!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2083, __extension__ __PRETTY_FUNCTION__))
;
2084 }
2085#endif
2086 // First build LCSSA for this loop so that we can preserve it when
2087 // forming dedicated exits. We don't want to perturb some other loop's
2088 // LCSSA while doing that CFG edit.
2089 formLCSSA(UpdateL, DT, &LI, nullptr);
2090
2091 // For loops reached by this loop's original exit blocks we may
2092 // introduced new, non-dedicated exits. At least try to re-form dedicated
2093 // exits for these loops. This may fail if they couldn't have dedicated
2094 // exits to start with.
2095 formDedicatedExitBlocks(&UpdateL, &DT, &LI, /*PreserveLCSSA*/ true);
2096 };
2097
2098 // For non-child cloned loops and hoisted loops, we just need to update LCSSA
2099 // and we can do it in any order as they don't nest relative to each other.
2100 //
2101 // Also check if any of the loops we have updated have become top-level loops
2102 // as that will necessitate widening the outer loop scope.
2103 for (Loop *UpdatedL :
2104 llvm::concat<Loop *>(NonChildClonedLoops, HoistedLoops)) {
2105 UpdateLoop(*UpdatedL);
2106 if (!UpdatedL->getParentLoop())
2107 OuterExitL = nullptr;
2108 }
2109 if (IsStillLoop) {
2110 UpdateLoop(L);
2111 if (!L.getParentLoop())
2112 OuterExitL = nullptr;
2113 }
2114
2115 // If the original loop had exit blocks, walk up through the outer most loop
2116 // of those exit blocks to update LCSSA and form updated dedicated exits.
2117 if (OuterExitL != &L)
2118 for (Loop *OuterL = ParentL; OuterL != OuterExitL;
2119 OuterL = OuterL->getParentLoop())
2120 UpdateLoop(*OuterL);
2121
2122#ifndef NDEBUG
2123 // Verify the entire loop structure to catch any incorrect updates before we
2124 // progress in the pass pipeline.
2125 LI.verify(DT);
2126#endif
2127
2128 // Now that we've unswitched something, make callbacks to report the changes.
2129 // For that we need to merge together the updated loops and the cloned loops
2130 // and check whether the original loop survived.
2131 SmallVector<Loop *, 4> SibLoops;
2132 for (Loop *UpdatedL : llvm::concat<Loop *>(NonChildClonedLoops, HoistedLoops))
2133 if (UpdatedL->getParentLoop() == ParentL)
2134 SibLoops.push_back(UpdatedL);
2135 UnswitchCB(IsStillLoop, SibLoops);
2136
2137 ++NumBranches;
2138 return true;
2139}
2140
2141/// Recursively compute the cost of a dominator subtree based on the per-block
2142/// cost map provided.
2143///
2144/// The recursive computation is memozied into the provided DT-indexed cost map
2145/// to allow querying it for most nodes in the domtree without it becoming
2146/// quadratic.
2147static int
2148computeDomSubtreeCost(DomTreeNode &N,
2149 const SmallDenseMap<BasicBlock *, int, 4> &BBCostMap,
2150 SmallDenseMap<DomTreeNode *, int, 4> &DTCostMap) {
2151 // Don't accumulate cost (or recurse through) blocks not in our block cost
2152 // map and thus not part of the duplication cost being considered.
2153 auto BBCostIt = BBCostMap.find(N.getBlock());
2154 if (BBCostIt == BBCostMap.end())
2155 return 0;
2156
2157 // Lookup this node to see if we already computed its cost.
2158 auto DTCostIt = DTCostMap.find(&N);
2159 if (DTCostIt != DTCostMap.end())
2160 return DTCostIt->second;
2161
2162 // If not, we have to compute it. We can't use insert above and update
2163 // because computing the cost may insert more things into the map.
2164 int Cost = std::accumulate(
2165 N.begin(), N.end(), BBCostIt->second, [&](int Sum, DomTreeNode *ChildN) {
2166 return Sum + computeDomSubtreeCost(*ChildN, BBCostMap, DTCostMap);
2167 });
2168 bool Inserted = DTCostMap.insert({&N, Cost}).second;
2169 (void)Inserted;
2170 assert(Inserted && "Should not insert a node while visiting children!")(static_cast <bool> (Inserted && "Should not insert a node while visiting children!"
) ? void (0) : __assert_fail ("Inserted && \"Should not insert a node while visiting children!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2170, __extension__ __PRETTY_FUNCTION__))
;
2171 return Cost;
2172}
2173
2174static bool
2175unswitchBestCondition(Loop &L, DominatorTree &DT, LoopInfo &LI,
2176 AssumptionCache &AC, TargetTransformInfo &TTI,
2177 function_ref<void(bool, ArrayRef<Loop *>)> UnswitchCB,
2178 ScalarEvolution *SE) {
2179 // Collect all invariant conditions within this loop (as opposed to an inner
2180 // loop which would be handled when visiting that inner loop).
2181 SmallVector<std::pair<TerminatorInst *, TinyPtrVector<Value *>>, 4>
2182 UnswitchCandidates;
2183 for (auto *BB : L.blocks()) {
13
Assuming '__begin1' is equal to '__end1'
2184 if (LI.getLoopFor(BB) != &L)
2185 continue;
2186
2187 if (auto *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
2188 // We can only consider fully loop-invariant switch conditions as we need
2189 // to completely eliminate the switch after unswitching.
2190 if (!isa<Constant>(SI->getCondition()) &&
2191 L.isLoopInvariant(SI->getCondition()))
2192 UnswitchCandidates.push_back({SI, {SI->getCondition()}});
2193 continue;
2194 }
2195
2196 auto *BI = dyn_cast<BranchInst>(BB->getTerminator());
2197 if (!BI || !BI->isConditional() || isa<Constant>(BI->getCondition()) ||
2198 BI->getSuccessor(0) == BI->getSuccessor(1))
2199 continue;
2200
2201 if (L.isLoopInvariant(BI->getCondition())) {
2202 UnswitchCandidates.push_back({BI, {BI->getCondition()}});
2203 continue;
2204 }
2205
2206 Instruction &CondI = *cast<Instruction>(BI->getCondition());
2207 if (CondI.getOpcode() != Instruction::And &&
2208 CondI.getOpcode() != Instruction::Or)
2209 continue;
2210
2211 TinyPtrVector<Value *> Invariants =
2212 collectHomogenousInstGraphLoopInvariants(L, CondI, LI);
2213 if (Invariants.empty())
2214 continue;
2215
2216 UnswitchCandidates.push_back({BI, std::move(Invariants)});
2217 }
2218
2219 // If we didn't find any candidates, we're done.
2220 if (UnswitchCandidates.empty())
14
Taking false branch
2221 return false;
2222
2223 // Check if there are irreducible CFG cycles in this loop. If so, we cannot
2224 // easily unswitch non-trivial edges out of the loop. Doing so might turn the
2225 // irreducible control flow into reducible control flow and introduce new
2226 // loops "out of thin air". If we ever discover important use cases for doing
2227 // this, we can add support to loop unswitch, but it is a lot of complexity
2228 // for what seems little or no real world benefit.
2229 LoopBlocksRPO RPOT(&L);
2230 RPOT.perform(&LI);
2231 if (containsIrreducibleCFG<const BasicBlock *>(RPOT, LI))
15
Taking false branch
2232 return false;
2233
2234 LLVM_DEBUG(do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "Considering " <<
UnswitchCandidates.size() << " non-trivial loop invariant conditions for unswitching.\n"
; } } while (false)
2235 dbgs() << "Considering " << UnswitchCandidates.size()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "Considering " <<
UnswitchCandidates.size() << " non-trivial loop invariant conditions for unswitching.\n"
; } } while (false)
2236 << " non-trivial loop invariant conditions for unswitching.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "Considering " <<
UnswitchCandidates.size() << " non-trivial loop invariant conditions for unswitching.\n"
; } } while (false)
;
2237
2238 // Given that unswitching these terminators will require duplicating parts of
2239 // the loop, so we need to be able to model that cost. Compute the ephemeral
2240 // values and set up a data structure to hold per-BB costs. We cache each
2241 // block's cost so that we don't recompute this when considering different
2242 // subsets of the loop for duplication during unswitching.
2243 SmallPtrSet<const Value *, 4> EphValues;
2244 CodeMetrics::collectEphemeralValues(&L, &AC, EphValues);
2245 SmallDenseMap<BasicBlock *, int, 4> BBCostMap;
2246
2247 // Compute the cost of each block, as well as the total loop cost. Also, bail
2248 // out if we see instructions which are incompatible with loop unswitching
2249 // (convergent, noduplicate, or cross-basic-block tokens).
2250 // FIXME: We might be able to safely handle some of these in non-duplicated
2251 // regions.
2252 int LoopCost = 0;
2253 for (auto *BB : L.blocks()) {
16
Assuming '__begin1' is equal to '__end1'
2254 int Cost = 0;
2255 for (auto &I : *BB) {
2256 if (EphValues.count(&I))
2257 continue;
2258
2259 if (I.getType()->isTokenTy() && I.isUsedOutsideOfBlock(BB))
2260 return false;
2261 if (auto CS = CallSite(&I))
2262 if (CS.isConvergent() || CS.cannotDuplicate())
2263 return false;
2264
2265 Cost += TTI.getUserCost(&I);
2266 }
2267 assert(Cost >= 0 && "Must not have negative costs!")(static_cast <bool> (Cost >= 0 && "Must not have negative costs!"
) ? void (0) : __assert_fail ("Cost >= 0 && \"Must not have negative costs!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2267, __extension__ __PRETTY_FUNCTION__))
;
2268 LoopCost += Cost;
2269 assert(LoopCost >= 0 && "Must not have negative loop costs!")(static_cast <bool> (LoopCost >= 0 && "Must not have negative loop costs!"
) ? void (0) : __assert_fail ("LoopCost >= 0 && \"Must not have negative loop costs!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2269, __extension__ __PRETTY_FUNCTION__))
;
2270 BBCostMap[BB] = Cost;
2271 }
2272 LLVM_DEBUG(dbgs() << " Total loop cost: " << LoopCost << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << " Total loop cost: "
<< LoopCost << "\n"; } } while (false)
;
2273
2274 // Now we find the best candidate by searching for the one with the following
2275 // properties in order:
2276 //
2277 // 1) An unswitching cost below the threshold
2278 // 2) The smallest number of duplicated unswitch candidates (to avoid
2279 // creating redundant subsequent unswitching)
2280 // 3) The smallest cost after unswitching.
2281 //
2282 // We prioritize reducing fanout of unswitch candidates provided the cost
2283 // remains below the threshold because this has a multiplicative effect.
2284 //
2285 // This requires memoizing each dominator subtree to avoid redundant work.
2286 //
2287 // FIXME: Need to actually do the number of candidates part above.
2288 SmallDenseMap<DomTreeNode *, int, 4> DTCostMap;
2289 // Given a terminator which might be unswitched, computes the non-duplicated
2290 // cost for that terminator.
2291 auto ComputeUnswitchedCost = [&](TerminatorInst &TI, bool FullUnswitch) {
2292 BasicBlock &BB = *TI.getParent();
2293 SmallPtrSet<BasicBlock *, 4> Visited;
2294
2295 int Cost = LoopCost;
2296 for (BasicBlock *SuccBB : successors(&BB)) {
2297 // Don't count successors more than once.
2298 if (!Visited.insert(SuccBB).second)
2299 continue;
2300
2301 // If this is a partial unswitch candidate, then it must be a conditional
2302 // branch with a condition of either `or` or `and`. In that case, one of
2303 // the successors is necessarily duplicated, so don't even try to remove
2304 // its cost.
2305 if (!FullUnswitch) {
2306 auto &BI = cast<BranchInst>(TI);
2307 if (cast<Instruction>(BI.getCondition())->getOpcode() ==
2308 Instruction::And) {
2309 if (SuccBB == BI.getSuccessor(1))
2310 continue;
2311 } else {
2312 assert(cast<Instruction>(BI.getCondition())->getOpcode() ==(static_cast <bool> (cast<Instruction>(BI.getCondition
())->getOpcode() == Instruction::Or && "Only `and` and `or` conditions can result in a partial "
"unswitch!") ? void (0) : __assert_fail ("cast<Instruction>(BI.getCondition())->getOpcode() == Instruction::Or && \"Only `and` and `or` conditions can result in a partial \" \"unswitch!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2315, __extension__ __PRETTY_FUNCTION__))
2313 Instruction::Or &&(static_cast <bool> (cast<Instruction>(BI.getCondition
())->getOpcode() == Instruction::Or && "Only `and` and `or` conditions can result in a partial "
"unswitch!") ? void (0) : __assert_fail ("cast<Instruction>(BI.getCondition())->getOpcode() == Instruction::Or && \"Only `and` and `or` conditions can result in a partial \" \"unswitch!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2315, __extension__ __PRETTY_FUNCTION__))
2314 "Only `and` and `or` conditions can result in a partial "(static_cast <bool> (cast<Instruction>(BI.getCondition
())->getOpcode() == Instruction::Or && "Only `and` and `or` conditions can result in a partial "
"unswitch!") ? void (0) : __assert_fail ("cast<Instruction>(BI.getCondition())->getOpcode() == Instruction::Or && \"Only `and` and `or` conditions can result in a partial \" \"unswitch!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2315, __extension__ __PRETTY_FUNCTION__))
2315 "unswitch!")(static_cast <bool> (cast<Instruction>(BI.getCondition
())->getOpcode() == Instruction::Or && "Only `and` and `or` conditions can result in a partial "
"unswitch!") ? void (0) : __assert_fail ("cast<Instruction>(BI.getCondition())->getOpcode() == Instruction::Or && \"Only `and` and `or` conditions can result in a partial \" \"unswitch!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2315, __extension__ __PRETTY_FUNCTION__))
;
2316 if (SuccBB == BI.getSuccessor(0))
2317 continue;
2318 }
2319 }
2320
2321 // This successor's domtree will not need to be duplicated after
2322 // unswitching if the edge to the successor dominates it (and thus the
2323 // entire tree). This essentially means there is no other path into this
2324 // subtree and so it will end up live in only one clone of the loop.
2325 if (SuccBB->getUniquePredecessor() ||
2326 llvm::all_of(predecessors(SuccBB), [&](BasicBlock *PredBB) {
2327 return PredBB == &BB || DT.dominates(SuccBB, PredBB);
2328 })) {
2329 Cost -= computeDomSubtreeCost(*DT[SuccBB], BBCostMap, DTCostMap);
2330 assert(Cost >= 0 &&(static_cast <bool> (Cost >= 0 && "Non-duplicated cost should never exceed total loop cost!"
) ? void (0) : __assert_fail ("Cost >= 0 && \"Non-duplicated cost should never exceed total loop cost!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2331, __extension__ __PRETTY_FUNCTION__))
2331 "Non-duplicated cost should never exceed total loop cost!")(static_cast <bool> (Cost >= 0 && "Non-duplicated cost should never exceed total loop cost!"
) ? void (0) : __assert_fail ("Cost >= 0 && \"Non-duplicated cost should never exceed total loop cost!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2331, __extension__ __PRETTY_FUNCTION__))
;
2332 }
2333 }
2334
2335 // Now scale the cost by the number of unique successors minus one. We
2336 // subtract one because there is already at least one copy of the entire
2337 // loop. This is computing the new cost of unswitching a condition.
2338 assert(Visited.size() > 1 &&(static_cast <bool> (Visited.size() > 1 && "Cannot unswitch a condition without multiple distinct successors!"
) ? void (0) : __assert_fail ("Visited.size() > 1 && \"Cannot unswitch a condition without multiple distinct successors!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2339, __extension__ __PRETTY_FUNCTION__))
2339 "Cannot unswitch a condition without multiple distinct successors!")(static_cast <bool> (Visited.size() > 1 && "Cannot unswitch a condition without multiple distinct successors!"
) ? void (0) : __assert_fail ("Visited.size() > 1 && \"Cannot unswitch a condition without multiple distinct successors!\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2339, __extension__ __PRETTY_FUNCTION__))
;
2340 return Cost * (Visited.size() - 1);
2341 };
2342 TerminatorInst *BestUnswitchTI = nullptr;
2343 int BestUnswitchCost;
17
'BestUnswitchCost' declared without an initial value
2344 ArrayRef<Value *> BestUnswitchInvariants;
2345 for (auto &TerminatorAndInvariants : UnswitchCandidates) {
18
Assuming '__begin1' is equal to '__end1'
2346 TerminatorInst &TI = *TerminatorAndInvariants.first;
2347 ArrayRef<Value *> Invariants = TerminatorAndInvariants.second;
2348 BranchInst *BI = dyn_cast<BranchInst>(&TI);
2349 int CandidateCost = ComputeUnswitchedCost(
2350 TI, /*FullUnswitch*/ !BI || (Invariants.size() == 1 &&
2351 Invariants[0] == BI->getCondition()));
2352 LLVM_DEBUG(dbgs() << " Computed cost of " << CandidateCostdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << " Computed cost of "
<< CandidateCost << " for unswitch candidate: " <<
TI << "\n"; } } while (false)
2353 << " for unswitch candidate: " << TI << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << " Computed cost of "
<< CandidateCost << " for unswitch candidate: " <<
TI << "\n"; } } while (false)
;
2354 if (!BestUnswitchTI || CandidateCost < BestUnswitchCost) {
2355 BestUnswitchTI = &TI;
2356 BestUnswitchCost = CandidateCost;
2357 BestUnswitchInvariants = Invariants;
2358 }
2359 }
2360
2361 if (BestUnswitchCost >= UnswitchThreshold) {
19
The left operand of '>=' is a garbage value
2362 LLVM_DEBUG(dbgs() << "Cannot unswitch, lowest cost found: "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "Cannot unswitch, lowest cost found: "
<< BestUnswitchCost << "\n"; } } while (false)
2363 << BestUnswitchCost << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "Cannot unswitch, lowest cost found: "
<< BestUnswitchCost << "\n"; } } while (false)
;
2364 return false;
2365 }
2366
2367 LLVM_DEBUG(dbgs() << " Trying to unswitch non-trivial (cost = "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << " Trying to unswitch non-trivial (cost = "
<< BestUnswitchCost << ") terminator: " <<
*BestUnswitchTI << "\n"; } } while (false)
2368 << BestUnswitchCost << ") terminator: " << *BestUnswitchTIdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << " Trying to unswitch non-trivial (cost = "
<< BestUnswitchCost << ") terminator: " <<
*BestUnswitchTI << "\n"; } } while (false)
2369 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << " Trying to unswitch non-trivial (cost = "
<< BestUnswitchCost << ") terminator: " <<
*BestUnswitchTI << "\n"; } } while (false)
;
2370 return unswitchNontrivialInvariants(
2371 L, *BestUnswitchTI, BestUnswitchInvariants, DT, LI, AC, UnswitchCB, SE);
2372}
2373
2374/// Unswitch control flow predicated on loop invariant conditions.
2375///
2376/// This first hoists all branches or switches which are trivial (IE, do not
2377/// require duplicating any part of the loop) out of the loop body. It then
2378/// looks at other loop invariant control flows and tries to unswitch those as
2379/// well by cloning the loop if the result is small enough.
2380///
2381/// The `DT`, `LI`, `AC`, `TTI` parameters are required analyses that are also
2382/// updated based on the unswitch.
2383///
2384/// If either `NonTrivial` is true or the flag `EnableNonTrivialUnswitch` is
2385/// true, we will attempt to do non-trivial unswitching as well as trivial
2386/// unswitching.
2387///
2388/// The `UnswitchCB` callback provided will be run after unswitching is
2389/// complete, with the first parameter set to `true` if the provided loop
2390/// remains a loop, and a list of new sibling loops created.
2391///
2392/// If `SE` is non-null, we will update that analysis based on the unswitching
2393/// done.
2394static bool unswitchLoop(Loop &L, DominatorTree &DT, LoopInfo &LI,
2395 AssumptionCache &AC, TargetTransformInfo &TTI,
2396 bool NonTrivial,
2397 function_ref<void(bool, ArrayRef<Loop *>)> UnswitchCB,
2398 ScalarEvolution *SE) {
2399 assert(L.isRecursivelyLCSSAForm(DT, LI) &&(static_cast <bool> (L.isRecursivelyLCSSAForm(DT, LI) &&
"Loops must be in LCSSA form before unswitching.") ? void (0
) : __assert_fail ("L.isRecursivelyLCSSAForm(DT, LI) && \"Loops must be in LCSSA form before unswitching.\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2400, __extension__ __PRETTY_FUNCTION__))
2400 "Loops must be in LCSSA form before unswitching.")(static_cast <bool> (L.isRecursivelyLCSSAForm(DT, LI) &&
"Loops must be in LCSSA form before unswitching.") ? void (0
) : __assert_fail ("L.isRecursivelyLCSSAForm(DT, LI) && \"Loops must be in LCSSA form before unswitching.\""
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2400, __extension__ __PRETTY_FUNCTION__))
;
2401 bool Changed = false;
2402
2403 // Must be in loop simplified form: we need a preheader and dedicated exits.
2404 if (!L.isLoopSimplifyForm())
6
Assuming the condition is false
7
Taking false branch
2405 return false;
2406
2407 // Try trivial unswitch first before loop over other basic blocks in the loop.
2408 if (unswitchAllTrivialConditions(L, DT, LI, SE)) {
8
Taking false branch
2409 // If we unswitched successfully we will want to clean up the loop before
2410 // processing it further so just mark it as unswitched and return.
2411 UnswitchCB(/*CurrentLoopValid*/ true, {});
2412 return true;
2413 }
2414
2415 // If we're not doing non-trivial unswitching, we're done. We both accept
2416 // a parameter but also check a local flag that can be used for testing
2417 // a debugging.
2418 if (!NonTrivial && !EnableNonTrivialUnswitch)
9
Assuming 'NonTrivial' is 0
10
Assuming the condition is false
11
Taking false branch
2419 return false;
2420
2421 // For non-trivial unswitching, because it often creates new loops, we rely on
2422 // the pass manager to iterate on the loops rather than trying to immediately
2423 // reach a fixed point. There is no substantial advantage to iterating
2424 // internally, and if any of the new loops are simplified enough to contain
2425 // trivial unswitching we want to prefer those.
2426
2427 // Try to unswitch the best invariant condition. We prefer this full unswitch to
2428 // a partial unswitch when possible below the threshold.
2429 if (unswitchBestCondition(L, DT, LI, AC, TTI, UnswitchCB, SE))
12
Calling 'unswitchBestCondition'
2430 return true;
2431
2432 // No other opportunities to unswitch.
2433 return Changed;
2434}
2435
2436PreservedAnalyses SimpleLoopUnswitchPass::run(Loop &L, LoopAnalysisManager &AM,
2437 LoopStandardAnalysisResults &AR,
2438 LPMUpdater &U) {
2439 Function &F = *L.getHeader()->getParent();
2440 (void)F;
2441
2442 LLVM_DEBUG(dbgs() << "Unswitching loop in " << F.getName() << ": " << Ldo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "Unswitching loop in "
<< F.getName() << ": " << L << "\n";
} } while (false)
2443 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "Unswitching loop in "
<< F.getName() << ": " << L << "\n";
} } while (false)
;
2444
2445 // Save the current loop name in a variable so that we can report it even
2446 // after it has been deleted.
2447 std::string LoopName = L.getName();
2448
2449 auto UnswitchCB = [&L, &U, &LoopName](bool CurrentLoopValid,
2450 ArrayRef<Loop *> NewLoops) {
2451 // If we did a non-trivial unswitch, we have added new (cloned) loops.
2452 if (!NewLoops.empty())
2453 U.addSiblingLoops(NewLoops);
2454
2455 // If the current loop remains valid, we should revisit it to catch any
2456 // other unswitch opportunities. Otherwise, we need to mark it as deleted.
2457 if (CurrentLoopValid)
2458 U.revisitCurrentLoop();
2459 else
2460 U.markLoopAsDeleted(L, LoopName);
2461 };
2462
2463 if (!unswitchLoop(L, AR.DT, AR.LI, AR.AC, AR.TTI, NonTrivial, UnswitchCB,
2464 &AR.SE))
2465 return PreservedAnalyses::all();
2466
2467 // Historically this pass has had issues with the dominator tree so verify it
2468 // in asserts builds.
2469 assert(AR.DT.verify(DominatorTree::VerificationLevel::Fast))(static_cast <bool> (AR.DT.verify(DominatorTree::VerificationLevel
::Fast)) ? void (0) : __assert_fail ("AR.DT.verify(DominatorTree::VerificationLevel::Fast)"
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2469, __extension__ __PRETTY_FUNCTION__))
;
2470 return getLoopPassPreservedAnalyses();
2471}
2472
2473namespace {
2474
2475class SimpleLoopUnswitchLegacyPass : public LoopPass {
2476 bool NonTrivial;
2477
2478public:
2479 static char ID; // Pass ID, replacement for typeid
2480
2481 explicit SimpleLoopUnswitchLegacyPass(bool NonTrivial = false)
2482 : LoopPass(ID), NonTrivial(NonTrivial) {
2483 initializeSimpleLoopUnswitchLegacyPassPass(
2484 *PassRegistry::getPassRegistry());
2485 }
2486
2487 bool runOnLoop(Loop *L, LPPassManager &LPM) override;
2488
2489 void getAnalysisUsage(AnalysisUsage &AU) const override {
2490 AU.addRequired<AssumptionCacheTracker>();
2491 AU.addRequired<TargetTransformInfoWrapperPass>();
2492 getLoopAnalysisUsage(AU);
2493 }
2494};
2495
2496} // end anonymous namespace
2497
2498bool SimpleLoopUnswitchLegacyPass::runOnLoop(Loop *L, LPPassManager &LPM) {
2499 if (skipLoop(L))
1
Assuming the condition is false
2
Taking false branch
2500 return false;
2501
2502 Function &F = *L->getHeader()->getParent();
2503
2504 LLVM_DEBUG(dbgs() << "Unswitching loop in " << F.getName() << ": " << *Ldo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "Unswitching loop in "
<< F.getName() << ": " << *L << "\n"
; } } while (false)
2505 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("simple-loop-unswitch")) { dbgs() << "Unswitching loop in "
<< F.getName() << ": " << *L << "\n"
; } } while (false)
;
2506
2507 auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
2508 auto &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
2509 auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
2510 auto &TTI = getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
2511
2512 auto *SEWP = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>();
2513 auto *SE = SEWP ? &SEWP->getSE() : nullptr;
3
Assuming 'SEWP' is null
4
'?' condition is false
2514
2515 auto UnswitchCB = [&L, &LPM](bool CurrentLoopValid,
2516 ArrayRef<Loop *> NewLoops) {
2517 // If we did a non-trivial unswitch, we have added new (cloned) loops.
2518 for (auto *NewL : NewLoops)
2519 LPM.addLoop(*NewL);
2520
2521 // If the current loop remains valid, re-add it to the queue. This is
2522 // a little wasteful as we'll finish processing the current loop as well,
2523 // but it is the best we can do in the old PM.
2524 if (CurrentLoopValid)
2525 LPM.addLoop(*L);
2526 else
2527 LPM.markLoopAsDeleted(*L);
2528 };
2529
2530 bool Changed = unswitchLoop(*L, DT, LI, AC, TTI, NonTrivial, UnswitchCB, SE);
5
Calling 'unswitchLoop'
2531
2532 // If anything was unswitched, also clear any cached information about this
2533 // loop.
2534 LPM.deleteSimpleAnalysisLoop(L);
2535
2536 // Historically this pass has had issues with the dominator tree so verify it
2537 // in asserts builds.
2538 assert(DT.verify(DominatorTree::VerificationLevel::Fast))(static_cast <bool> (DT.verify(DominatorTree::VerificationLevel
::Fast)) ? void (0) : __assert_fail ("DT.verify(DominatorTree::VerificationLevel::Fast)"
, "/build/llvm-toolchain-snapshot-7~svn338205/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp"
, 2538, __extension__ __PRETTY_FUNCTION__))
;
2539
2540 return Changed;
2541}
2542
2543char SimpleLoopUnswitchLegacyPass::ID = 0;
2544INITIALIZE_PASS_BEGIN(SimpleLoopUnswitchLegacyPass, "simple-loop-unswitch",static void *initializeSimpleLoopUnswitchLegacyPassPassOnce(PassRegistry
&Registry) {
2545 "Simple unswitch loops", false, false)static void *initializeSimpleLoopUnswitchLegacyPassPassOnce(PassRegistry
&Registry) {
2546INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)initializeAssumptionCacheTrackerPass(Registry);
2547INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)initializeDominatorTreeWrapperPassPass(Registry);
2548INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)initializeLoopInfoWrapperPassPass(Registry);
2549INITIALIZE_PASS_DEPENDENCY(LoopPass)initializeLoopPassPass(Registry);
2550INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)initializeTargetTransformInfoWrapperPassPass(Registry);
2551INITIALIZE_PASS_END(SimpleLoopUnswitchLegacyPass, "simple-loop-unswitch",PassInfo *PI = new PassInfo( "Simple unswitch loops", "simple-loop-unswitch"
, &SimpleLoopUnswitchLegacyPass::ID, PassInfo::NormalCtor_t
(callDefaultCtor<SimpleLoopUnswitchLegacyPass>), false,
false); Registry.registerPass(*PI, true); return PI; } static
llvm::once_flag InitializeSimpleLoopUnswitchLegacyPassPassFlag
; void llvm::initializeSimpleLoopUnswitchLegacyPassPass(PassRegistry
&Registry) { llvm::call_once(InitializeSimpleLoopUnswitchLegacyPassPassFlag
, initializeSimpleLoopUnswitchLegacyPassPassOnce, std::ref(Registry
)); }
2552 "Simple unswitch loops", false, false)PassInfo *PI = new PassInfo( "Simple unswitch loops", "simple-loop-unswitch"
, &SimpleLoopUnswitchLegacyPass::ID, PassInfo::NormalCtor_t
(callDefaultCtor<SimpleLoopUnswitchLegacyPass>), false,
false); Registry.registerPass(*PI, true); return PI; } static
llvm::once_flag InitializeSimpleLoopUnswitchLegacyPassPassFlag
; void llvm::initializeSimpleLoopUnswitchLegacyPassPass(PassRegistry
&Registry) { llvm::call_once(InitializeSimpleLoopUnswitchLegacyPassPassFlag
, initializeSimpleLoopUnswitchLegacyPassPassOnce, std::ref(Registry
)); }
2553
2554Pass *llvm::createSimpleLoopUnswitchLegacyPass(bool NonTrivial) {
2555 return new SimpleLoopUnswitchLegacyPass(NonTrivial);
2556}