LLVM  13.0.0git
LoopInstSimplify.cpp
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1 //===- LoopInstSimplify.cpp - Loop Instruction Simplification Pass --------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This pass performs lightweight instruction simplification on loop bodies.
10 //
11 //===----------------------------------------------------------------------===//
12 
15 #include "llvm/ADT/STLExtras.h"
16 #include "llvm/ADT/SmallPtrSet.h"
17 #include "llvm/ADT/SmallVector.h"
18 #include "llvm/ADT/Statistic.h"
21 #include "llvm/Analysis/LoopInfo.h"
23 #include "llvm/Analysis/LoopPass.h"
27 #include "llvm/IR/BasicBlock.h"
28 #include "llvm/IR/CFG.h"
29 #include "llvm/IR/DataLayout.h"
30 #include "llvm/IR/Dominators.h"
31 #include "llvm/IR/Instruction.h"
32 #include "llvm/IR/Instructions.h"
33 #include "llvm/IR/Module.h"
34 #include "llvm/IR/PassManager.h"
35 #include "llvm/IR/User.h"
36 #include "llvm/InitializePasses.h"
37 #include "llvm/Pass.h"
38 #include "llvm/Support/Casting.h"
39 #include "llvm/Transforms/Scalar.h"
42 #include <algorithm>
43 #include <utility>
44 
45 using namespace llvm;
46 
47 #define DEBUG_TYPE "loop-instsimplify"
48 
49 STATISTIC(NumSimplified, "Number of redundant instructions simplified");
50 
51 static bool simplifyLoopInst(Loop &L, DominatorTree &DT, LoopInfo &LI,
52  AssumptionCache &AC, const TargetLibraryInfo &TLI,
53  MemorySSAUpdater *MSSAU) {
54  const DataLayout &DL = L.getHeader()->getModule()->getDataLayout();
55  SimplifyQuery SQ(DL, &TLI, &DT, &AC);
56 
57  // On the first pass over the loop body we try to simplify every instruction.
58  // On subsequent passes, we can restrict this to only simplifying instructions
59  // where the inputs have been updated. We end up needing two sets: one
60  // containing the instructions we are simplifying in *this* pass, and one for
61  // the instructions we will want to simplify in the *next* pass. We use
62  // pointers so we can swap between two stably allocated sets.
63  SmallPtrSet<const Instruction *, 8> S1, S2, *ToSimplify = &S1, *Next = &S2;
64 
65  // Track the PHI nodes that have already been visited during each iteration so
66  // that we can identify when it is necessary to iterate.
67  SmallPtrSet<PHINode *, 4> VisitedPHIs;
68 
69  // While simplifying we may discover dead code or cause code to become dead.
70  // Keep track of all such instructions and we will delete them at the end.
72 
73  // First we want to create an RPO traversal of the loop body. By processing in
74  // RPO we can ensure that definitions are processed prior to uses (for non PHI
75  // uses) in all cases. This ensures we maximize the simplifications in each
76  // iteration over the loop and minimizes the possible causes for continuing to
77  // iterate.
78  LoopBlocksRPO RPOT(&L);
79  RPOT.perform(&LI);
80  MemorySSA *MSSA = MSSAU ? MSSAU->getMemorySSA() : nullptr;
81 
82  bool Changed = false;
83  for (;;) {
84  if (MSSAU && VerifyMemorySSA)
85  MSSA->verifyMemorySSA();
86  for (BasicBlock *BB : RPOT) {
87  for (Instruction &I : *BB) {
88  if (auto *PI = dyn_cast<PHINode>(&I))
89  VisitedPHIs.insert(PI);
90 
91  if (I.use_empty()) {
92  if (isInstructionTriviallyDead(&I, &TLI))
93  DeadInsts.push_back(&I);
94  continue;
95  }
96 
97  // We special case the first iteration which we can detect due to the
98  // empty `ToSimplify` set.
99  bool IsFirstIteration = ToSimplify->empty();
100 
101  if (!IsFirstIteration && !ToSimplify->count(&I))
102  continue;
103 
105  if (!V || !LI.replacementPreservesLCSSAForm(&I, V))
106  continue;
107 
108  for (Value::use_iterator UI = I.use_begin(), UE = I.use_end();
109  UI != UE;) {
110  Use &U = *UI++;
111  auto *UserI = cast<Instruction>(U.getUser());
112  U.set(V);
113 
114  // If the instruction is used by a PHI node we have already processed
115  // we'll need to iterate on the loop body to converge, so add it to
116  // the next set.
117  if (auto *UserPI = dyn_cast<PHINode>(UserI))
118  if (VisitedPHIs.count(UserPI)) {
119  Next->insert(UserPI);
120  continue;
121  }
122 
123  // If we are only simplifying targeted instructions and the user is an
124  // instruction in the loop body, add it to our set of targeted
125  // instructions. Because we process defs before uses (outside of PHIs)
126  // we won't have visited it yet.
127  //
128  // We also skip any uses outside of the loop being simplified. Those
129  // should always be PHI nodes due to LCSSA form, and we don't want to
130  // try to simplify those away.
131  assert((L.contains(UserI) || isa<PHINode>(UserI)) &&
132  "Uses outside the loop should be PHI nodes due to LCSSA!");
133  if (!IsFirstIteration && L.contains(UserI))
134  ToSimplify->insert(UserI);
135  }
136 
137  if (MSSAU)
138  if (Instruction *SimpleI = dyn_cast_or_null<Instruction>(V))
139  if (MemoryAccess *MA = MSSA->getMemoryAccess(&I))
140  if (MemoryAccess *ReplacementMA = MSSA->getMemoryAccess(SimpleI))
141  MA->replaceAllUsesWith(ReplacementMA);
142 
143  assert(I.use_empty() && "Should always have replaced all uses!");
144  if (isInstructionTriviallyDead(&I, &TLI))
145  DeadInsts.push_back(&I);
146  ++NumSimplified;
147  Changed = true;
148  }
149  }
150 
151  // Delete any dead instructions found thus far now that we've finished an
152  // iteration over all instructions in all the loop blocks.
153  if (!DeadInsts.empty()) {
154  Changed = true;
155  RecursivelyDeleteTriviallyDeadInstructions(DeadInsts, &TLI, MSSAU);
156  }
157 
158  if (MSSAU && VerifyMemorySSA)
159  MSSA->verifyMemorySSA();
160 
161  // If we never found a PHI that needs to be simplified in the next
162  // iteration, we're done.
163  if (Next->empty())
164  break;
165 
166  // Otherwise, put the next set in place for the next iteration and reset it
167  // and the visited PHIs for that iteration.
168  std::swap(Next, ToSimplify);
169  Next->clear();
170  VisitedPHIs.clear();
171  DeadInsts.clear();
172  }
173 
174  return Changed;
175 }
176 
177 namespace {
178 
179 class LoopInstSimplifyLegacyPass : public LoopPass {
180 public:
181  static char ID; // Pass ID, replacement for typeid
182 
183  LoopInstSimplifyLegacyPass() : LoopPass(ID) {
185  }
186 
187  bool runOnLoop(Loop *L, LPPassManager &LPM) override {
188  if (skipLoop(L))
189  return false;
190  DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
191  LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
192  AssumptionCache &AC =
193  getAnalysis<AssumptionCacheTracker>().getAssumptionCache(
194  *L->getHeader()->getParent());
195  const TargetLibraryInfo &TLI =
196  getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(
197  *L->getHeader()->getParent());
198  MemorySSA *MSSA = nullptr;
201  MSSA = &getAnalysis<MemorySSAWrapperPass>().getMSSA();
202  MSSAU = MemorySSAUpdater(MSSA);
203  }
204 
205  return simplifyLoopInst(*L, DT, LI, AC, TLI,
206  MSSAU.hasValue() ? MSSAU.getPointer() : nullptr);
207  }
208 
209  void getAnalysisUsage(AnalysisUsage &AU) const override {
213  AU.setPreservesCFG();
217  }
219  }
220 };
221 
222 } // end anonymous namespace
223 
226  LPMUpdater &) {
228  if (AR.MSSA) {
229  MSSAU = MemorySSAUpdater(AR.MSSA);
230  if (VerifyMemorySSA)
231  AR.MSSA->verifyMemorySSA();
232  }
233  if (!simplifyLoopInst(L, AR.DT, AR.LI, AR.AC, AR.TLI,
234  MSSAU.hasValue() ? MSSAU.getPointer() : nullptr))
235  return PreservedAnalyses::all();
236 
237  auto PA = getLoopPassPreservedAnalyses();
238  PA.preserveSet<CFGAnalyses>();
239  if (AR.MSSA)
240  PA.preserve<MemorySSAAnalysis>();
241  return PA;
242 }
243 
245 
246 INITIALIZE_PASS_BEGIN(LoopInstSimplifyLegacyPass, "loop-instsimplify",
247  "Simplify instructions in loops", false, false)
252 INITIALIZE_PASS_END(LoopInstSimplifyLegacyPass, "loop-instsimplify",
254 
256  return new LoopInstSimplifyLegacyPass();
257 }
llvm::PreservedAnalyses
A set of analyses that are preserved following a run of a transformation pass.
Definition: PassManager.h:155
llvm::RecursivelyDeleteTriviallyDeadInstructions
bool RecursivelyDeleteTriviallyDeadInstructions(Value *V, const TargetLibraryInfo *TLI=nullptr, MemorySSAUpdater *MSSAU=nullptr, std::function< void(Value *)> AboutToDeleteCallback=std::function< void(Value *)>())
If the specified value is a trivially dead instruction, delete it.
Definition: Local.cpp:496
AssumptionCache.h
llvm
Definition: AllocatorList.h:23
llvm::LoopStandardAnalysisResults::AC
AssumptionCache & AC
Definition: LoopAnalysisManager.h:54
llvm::DataLayout
A parsed version of the target data layout string in and methods for querying it.
Definition: DataLayout.h:112
llvm::LoopInstSimplifyPass::run
PreservedAnalyses run(Loop &L, LoopAnalysisManager &AM, LoopStandardAnalysisResults &AR, LPMUpdater &U)
Definition: LoopInstSimplify.cpp:224
llvm::BasicBlock::getParent
const Function * getParent() const
Return the enclosing method, or null if none.
Definition: BasicBlock.h:107
llvm::SimplifyQuery
Definition: InstructionSimplify.h:94
Scalar.h
MemorySSAUpdater.h
llvm::Loop
Represents a single loop in the control flow graph.
Definition: LoopInfo.h:530
Pass.h
llvm::LoopBase::contains
bool contains(const LoopT *L) const
Return true if the specified loop is contained within in this loop.
Definition: LoopInfo.h:122
llvm::SmallVector
This is a 'vector' (really, a variable-sized array), optimized for the case when the array is small.
Definition: SmallVector.h:1168
Statistic.h
Local.h
llvm::DominatorTree
Concrete subclass of DominatorTreeBase that is used to compute a normal dominator tree.
Definition: Dominators.h:151
llvm::getLoopAnalysisUsage
void getLoopAnalysisUsage(AnalysisUsage &AU)
Helper to consistently add the set of standard passes to a loop pass's AnalysisUsage.
Definition: LoopUtils.cpp:150
Module.h
llvm::LoopStandardAnalysisResults
The adaptor from a function pass to a loop pass computes these analyses and makes them available to t...
Definition: LoopAnalysisManager.h:52
llvm::Optional
Definition: APInt.h:33
llvm::SmallPtrSet
SmallPtrSet - This class implements a set which is optimized for holding SmallSize or less elements.
Definition: SmallPtrSet.h:449
STLExtras.h
llvm::EnableMSSALoopDependency
cl::opt< bool > EnableMSSALoopDependency
Enables memory ssa as a dependency for loop passes.
LoopInstSimplify.h
loops
loop Simplify instructions in loops
Definition: LoopInstSimplify.cpp:253
llvm::LoopStandardAnalysisResults::DT
DominatorTree & DT
Definition: LoopAnalysisManager.h:55
loop
Analysis the ScalarEvolution expression for r is< loop > Outside the loop
Definition: README.txt:8
llvm::BasicBlock
LLVM Basic Block Representation.
Definition: BasicBlock.h:58
llvm::Optional::getPointer
constexpr const T * getPointer() const
Definition: Optional.h:278
llvm::LoopBlocksRPO
Wrapper class to LoopBlocksDFS that provides a standard begin()/end() interface for the DFS reverse p...
Definition: LoopIterator.h:172
llvm::Optional::hasValue
constexpr bool hasValue() const
Definition: Optional.h:286
PointerIntPair.h
Instruction.h
llvm::MemorySSAWrapperPass
Legacy analysis pass which computes MemorySSA.
Definition: MemorySSA.h:961
llvm::PassRegistry::getPassRegistry
static PassRegistry * getPassRegistry()
getPassRegistry - Access the global registry object, which is automatically initialized at applicatio...
Definition: PassRegistry.cpp:31
llvm::Value::use_iterator
use_iterator_impl< Use > use_iterator
Definition: Value.h:366
llvm::AnalysisUsage
Represent the analysis usage information of a pass.
Definition: PassAnalysisSupport.h:47
INITIALIZE_PASS_BEGIN
INITIALIZE_PASS_BEGIN(LoopInstSimplifyLegacyPass, "loop-instsimplify", "Simplify instructions in loops", false, false) INITIALIZE_PASS_END(LoopInstSimplifyLegacyPass
TargetLibraryInfo.h
llvm::LoopInfo::replacementPreservesLCSSAForm
bool replacementPreservesLCSSAForm(Instruction *From, Value *To)
Returns true if replacing From with To everywhere is guaranteed to preserve LCSSA form.
Definition: LoopInfo.h:1112
false
Definition: StackSlotColoring.cpp:142
in
The object format emitted by the WebAssembly backed is documented in
Definition: README.txt:11
llvm::Instruction
Definition: Instruction.h:45
simplifyLoopInst
static bool simplifyLoopInst(Loop &L, DominatorTree &DT, LoopInfo &LI, AssumptionCache &AC, const TargetLibraryInfo &TLI, MemorySSAUpdater *MSSAU)
Definition: LoopInstSimplify.cpp:51
llvm::SimplifyInstruction
Value * SimplifyInstruction(Instruction *I, const SimplifyQuery &Q, OptimizationRemarkEmitter *ORE=nullptr)
See if we can compute a simplified version of this instruction.
Definition: InstructionSimplify.cpp:5788
llvm::DominatorTreeWrapperPass
Legacy analysis pass which computes a DominatorTree.
Definition: Dominators.h:281
llvm::STATISTIC
STATISTIC(NumFunctions, "Total number of functions")
llvm::Use::getUser
User * getUser() const
Returns the User that contains this Use.
Definition: Use.h:73
LoopUtils.h
llvm::LPPassManager
Definition: LoopPass.h:75
SmallPtrSet.h
llvm::BasicBlock::getModule
const Module * getModule() const
Return the module owning the function this basic block belongs to, or nullptr if the function does no...
Definition: BasicBlock.cpp:144
LoopIterator.h
INITIALIZE_PASS_END
#define INITIALIZE_PASS_END(passName, arg, name, cfg, analysis)
Definition: PassSupport.h:58
CFG.h
LoopInfo.h
llvm::getLoopPassPreservedAnalyses
PreservedAnalyses getLoopPassPreservedAnalyses()
Returns the minimum set of Analyses that all loop passes must preserve.
Definition: LoopAnalysisManager.cpp:140
llvm::Use::set
void set(Value *Val)
Definition: Value.h:872
BasicBlock.h
llvm::instructions
inst_range instructions(Function *F)
Definition: InstIterator.h:133
llvm::TargetLibraryInfoWrapperPass
Definition: TargetLibraryInfo.h:446
llvm::LoopPass
Definition: LoopPass.h:27
llvm::MemorySSAUpdater
Definition: MemorySSAUpdater.h:56
llvm::LPMUpdater
This class provides an interface for updating the loop pass manager based on mutations to the loop ne...
Definition: LoopPassManager.h:243
llvm::MemorySSAUpdater::getMemorySSA
MemorySSA * getMemorySSA() const
Get handle on MemorySSA.
Definition: MemorySSAUpdater.h:249
INITIALIZE_PASS_DEPENDENCY
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
llvm::MemorySSA
Encapsulates MemorySSA, including all data associated with memory accesses.
Definition: MemorySSA.h:704
I
#define I(x, y, z)
Definition: MD5.cpp:59
llvm::MemorySSA::getMemoryAccess
MemoryUseOrDef * getMemoryAccess(const Instruction *I) const
Given a memory Mod/Ref'ing instruction, get the MemorySSA access associated with it.
Definition: MemorySSA.h:721
assert
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
std::swap
void swap(llvm::BitVector &LHS, llvm::BitVector &RHS)
Implement std::swap in terms of BitVector swap.
Definition: BitVector.h:840
llvm::SimplifyQuery::getWithInstruction
SimplifyQuery getWithInstruction(Instruction *I) const
Definition: InstructionSimplify.h:121
llvm::MemorySSA::verifyMemorySSA
void verifyMemorySSA() const
Verify that MemorySSA is self consistent (IE definitions dominate all uses, uses appear in the right ...
Definition: MemorySSA.cpp:1867
llvm::MemorySSAAnalysis
An analysis that produces MemorySSA for a function.
Definition: MemorySSA.h:922
llvm::SmallPtrSetImpl::count
size_type count(ConstPtrType Ptr) const
count - Return 1 if the specified pointer is in the set, 0 otherwise.
Definition: SmallPtrSet.h:382
llvm::SmallPtrSetImplBase::clear
void clear()
Definition: SmallPtrSet.h:94
llvm::AssumptionCacheTracker
An immutable pass that tracks lazily created AssumptionCache objects.
Definition: AssumptionCache.h:200
llvm::isInstructionTriviallyDead
bool isInstructionTriviallyDead(Instruction *I, const TargetLibraryInfo *TLI=nullptr)
Return true if the result produced by the instruction is not used, and the instruction has no side ef...
Definition: Local.cpp:398
llvm::LoopInfo
Definition: LoopInfo.h:1080
DataLayout.h
llvm::AnalysisUsage::setPreservesCFG
void setPreservesCFG()
This function should be called by the pass, iff they do not:
Definition: Pass.cpp:253
llvm::AssumptionCache
A cache of @llvm.assume calls within a function.
Definition: AssumptionCache.h:41
Simplify
assume Assume Simplify
Definition: AssumeBundleBuilder.cpp:604
LoopPass.h
llvm::CFGAnalyses
Represents analyses that only rely on functions' control flow.
Definition: PassManager.h:116
llvm::AnalysisUsage::addPreserved
AnalysisUsage & addPreserved()
Add the specified Pass class to the set of analyses preserved by this pass.
Definition: PassAnalysisSupport.h:98
DL
MachineBasicBlock MachineBasicBlock::iterator DebugLoc DL
Definition: AArch64SLSHardening.cpp:76
llvm::LoopStandardAnalysisResults::LI
LoopInfo & LI
Definition: LoopAnalysisManager.h:56
llvm::MemoryAccess
Definition: MemorySSA.h:140
llvm::PreservedAnalyses::all
static PreservedAnalyses all()
Construct a special preserved set that preserves all passes.
Definition: PassManager.h:161
llvm::initializeLoopInstSimplifyLegacyPassPass
void initializeLoopInstSimplifyLegacyPassPass(PassRegistry &)
Casting.h
llvm::LoopBase::getHeader
BlockT * getHeader() const
Definition: LoopInfo.h:104
PassManager.h
llvm::TargetLibraryInfo
Provides information about what library functions are available for the current target.
Definition: TargetLibraryInfo.h:207
llvm::SmallVectorImpl::clear
void clear()
Definition: SmallVector.h:585
instsimplify
loop instsimplify
Definition: LoopInstSimplify.cpp:252
llvm::createLoopInstSimplifyPass
Pass * createLoopInstSimplifyPass()
Definition: LoopInstSimplify.cpp:255
llvm::Pass
Pass interface - Implemented by all 'passes'.
Definition: Pass.h:91
MemorySSA.h
Instructions.h
SmallVector.h
User.h
Dominators.h
llvm::SmallPtrSetImplBase::empty
LLVM_NODISCARD bool empty() const
Definition: SmallPtrSet.h:91
InstructionSimplify.h
llvm::LoopStandardAnalysisResults::MSSA
MemorySSA * MSSA
Definition: LoopAnalysisManager.h:61
llvm::Module::getDataLayout
const DataLayout & getDataLayout() const
Get the data layout for the module's target platform.
Definition: Module.cpp:397
llvm::AnalysisManager
A container for analyses that lazily runs them and caches their results.
Definition: InstructionSimplify.h:44
BB
Common register allocation spilling lr str ldr sxth r3 ldr mla r4 can lr mov lr str ldr sxth r3 mla r4 and then merge mul and lr str ldr sxth r3 mla r4 It also increase the likelihood the store may become dead bb27 Successors according to LLVM BB
Definition: README.txt:39
llvm::AnalysisUsage::addRequired
AnalysisUsage & addRequired()
Definition: PassAnalysisSupport.h:75
llvm::VerifyMemorySSA
bool VerifyMemorySSA
Enables verification of MemorySSA.
Definition: MemorySSA.cpp:91
llvm::LoopBlocksRPO::perform
void perform(LoopInfo *LI)
Traverse the loop blocks and store the DFS result.
Definition: LoopIterator.h:180
llvm::LoopStandardAnalysisResults::TLI
TargetLibraryInfo & TLI
Definition: LoopAnalysisManager.h:58
InitializePasses.h
llvm::Value
LLVM Value Representation.
Definition: Value.h:75
llvm::Use
A Use represents the edge between a Value definition and its users.
Definition: Use.h:44
llvm::SmallPtrSetImpl::insert
std::pair< iterator, bool > insert(PtrType Ptr)
Inserts Ptr if and only if there is no element in the container equal to Ptr.
Definition: SmallPtrSet.h:364
llvm::Intrinsic::ID
unsigned ID
Definition: TargetTransformInfo.h:38