LLVM 19.0.0git
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1//===- GVN.h - Eliminate redundant values and loads -------------*- C++ -*-===//
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
8/// \file
9/// This file provides the interface for LLVM's Global Value Numbering pass
10/// which eliminates fully redundant instructions. It also does somewhat Ad-Hoc
11/// PRE and dead load elimination.
18#include "llvm/ADT/DenseMap.h"
19#include "llvm/ADT/MapVector.h"
20#include "llvm/ADT/SetVector.h"
22#include "llvm/IR/Dominators.h"
23#include "llvm/IR/InstrTypes.h"
24#include "llvm/IR/PassManager.h"
25#include "llvm/IR/ValueHandle.h"
28#include <cstdint>
29#include <optional>
30#include <utility>
31#include <vector>
33namespace llvm {
35class AAResults;
36class AssumeInst;
37class AssumptionCache;
38class BasicBlock;
39class BranchInst;
40class CallInst;
41class ExtractValueInst;
42class Function;
43class FunctionPass;
44class GetElementPtrInst;
45class ImplicitControlFlowTracking;
46class LoadInst;
47class LoopInfo;
48class MemDepResult;
49class MemoryDependenceResults;
50class MemorySSA;
51class MemorySSAUpdater;
52class NonLocalDepResult;
53class OptimizationRemarkEmitter;
54class PHINode;
55class TargetLibraryInfo;
56class Value;
57/// A private "module" namespace for types and utilities used by GVN. These
58/// are implementation details and should not be used by clients.
61struct AvailableValue;
63class GVNLegacyPass;
65} // end namespace gvn
67/// A set of parameters to control various transforms performed by GVN pass.
68// Each of the optional boolean parameters can be set to:
69/// true - enabling the transformation.
70/// false - disabling the transformation.
71/// None - relying on a global default.
72/// Intended use is to create a default object, modify parameters with
73/// additional setters and then pass it to GVN.
74struct GVNOptions {
75 std::optional<bool> AllowPRE;
76 std::optional<bool> AllowLoadPRE;
77 std::optional<bool> AllowLoadInLoopPRE;
78 std::optional<bool> AllowLoadPRESplitBackedge;
79 std::optional<bool> AllowMemDep;
81 GVNOptions() = default;
83 /// Enables or disables PRE in GVN.
84 GVNOptions &setPRE(bool PRE) {
85 AllowPRE = PRE;
86 return *this;
87 }
89 /// Enables or disables PRE of loads in GVN.
90 GVNOptions &setLoadPRE(bool LoadPRE) {
91 AllowLoadPRE = LoadPRE;
92 return *this;
93 }
95 GVNOptions &setLoadInLoopPRE(bool LoadInLoopPRE) {
96 AllowLoadInLoopPRE = LoadInLoopPRE;
97 return *this;
98 }
100 /// Enables or disables PRE of loads in GVN.
101 GVNOptions &setLoadPRESplitBackedge(bool LoadPRESplitBackedge) {
102 AllowLoadPRESplitBackedge = LoadPRESplitBackedge;
103 return *this;
104 }
106 /// Enables or disables use of MemDepAnalysis.
107 GVNOptions &setMemDep(bool MemDep) {
108 AllowMemDep = MemDep;
109 return *this;
110 }
113/// The core GVN pass object.
115/// FIXME: We should have a good summary of the GVN algorithm implemented by
116/// this particular pass here.
117class GVNPass : public PassInfoMixin<GVNPass> {
118 GVNOptions Options;
121 struct Expression;
125 /// Run the pass over the function.
126 PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
128 void printPipeline(raw_ostream &OS,
129 function_ref<StringRef(StringRef)> MapClassName2PassName);
131 /// This removes the specified instruction from
132 /// our various maps and marks it for deletion.
134 VN.erase(I);
135 InstrsToErase.push_back(I);
136 }
138 DominatorTree &getDominatorTree() const { return *DT; }
140 MemoryDependenceResults &getMemDep() const { return *MD; }
142 bool isPREEnabled() const;
143 bool isLoadPREEnabled() const;
144 bool isLoadInLoopPREEnabled() const;
146 bool isMemDepEnabled() const;
148 /// This class holds the mapping between values and value numbers. It is used
149 /// as an efficient mechanism to determine the expression-wise equivalence of
150 /// two values.
152 DenseMap<Value *, uint32_t> valueNumbering;
153 DenseMap<Expression, uint32_t> expressionNumbering;
155 // Expressions is the vector of Expression. ExprIdx is the mapping from
156 // value number to the index of Expression in Expressions. We use it
157 // instead of a DenseMap because filling such mapping is faster than
158 // filling a DenseMap and the compile time is a little better.
159 uint32_t nextExprNumber = 0;
161 std::vector<Expression> Expressions;
162 std::vector<uint32_t> ExprIdx;
164 // Value number to PHINode mapping. Used for phi-translate in scalarpre.
167 // Cache for phi-translate in scalarpre.
168 using PhiTranslateMap =
170 PhiTranslateMap PhiTranslateTable;
172 AAResults *AA = nullptr;
173 MemoryDependenceResults *MD = nullptr;
174 DominatorTree *DT = nullptr;
176 uint32_t nextValueNumber = 1;
178 Expression createExpr(Instruction *I);
179 Expression createCmpExpr(unsigned Opcode, CmpInst::Predicate Predicate,
180 Value *LHS, Value *RHS);
181 Expression createExtractvalueExpr(ExtractValueInst *EI);
182 Expression createGEPExpr(GetElementPtrInst *GEP);
183 uint32_t lookupOrAddCall(CallInst *C);
184 uint32_t phiTranslateImpl(const BasicBlock *BB, const BasicBlock *PhiBlock,
185 uint32_t Num, GVNPass &Gvn);
186 bool areCallValsEqual(uint32_t Num, uint32_t NewNum, const BasicBlock *Pred,
187 const BasicBlock *PhiBlock, GVNPass &Gvn);
188 std::pair<uint32_t, bool> assignExpNewValueNum(Expression &exp);
189 bool areAllValsInBB(uint32_t num, const BasicBlock *BB, GVNPass &Gvn);
191 public:
199 uint32_t lookup(Value *V, bool Verify = true) const;
200 uint32_t lookupOrAddCmp(unsigned Opcode, CmpInst::Predicate Pred,
201 Value *LHS, Value *RHS);
202 uint32_t phiTranslate(const BasicBlock *BB, const BasicBlock *PhiBlock,
203 uint32_t Num, GVNPass &Gvn);
204 void eraseTranslateCacheEntry(uint32_t Num, const BasicBlock &CurrBlock);
205 bool exists(Value *V) const;
206 void add(Value *V, uint32_t num);
207 void clear();
208 void erase(Value *v);
209 void setAliasAnalysis(AAResults *A) { AA = A; }
210 AAResults *getAliasAnalysis() const { return AA; }
212 void setDomTree(DominatorTree *D) { DT = D; }
213 uint32_t getNextUnusedValueNumber() { return nextValueNumber; }
214 void verifyRemoved(const Value *) const;
215 };
218 friend class gvn::GVNLegacyPass;
219 friend struct DenseMapInfo<Expression>;
221 MemoryDependenceResults *MD = nullptr;
222 DominatorTree *DT = nullptr;
223 const TargetLibraryInfo *TLI = nullptr;
224 AssumptionCache *AC = nullptr;
225 SetVector<BasicBlock *> DeadBlocks;
226 OptimizationRemarkEmitter *ORE = nullptr;
227 ImplicitControlFlowTracking *ICF = nullptr;
228 LoopInfo *LI = nullptr;
229 MemorySSAUpdater *MSSAU = nullptr;
231 ValueTable VN;
233 /// A mapping from value numbers to lists of Value*'s that
234 /// have that value number. Use findLeader to query it.
235 struct LeaderTableEntry {
236 Value *Val;
237 const BasicBlock *BB;
238 LeaderTableEntry *Next;
239 };
241 BumpPtrAllocator TableAllocator;
243 // Block-local map of equivalent values to their leader, does not
244 // propagate to any successors. Entries added mid-block are applied
245 // to the remaining instructions in the block.
246 SmallMapVector<Value *, Value *, 4> ReplaceOperandsWithMap;
247 SmallVector<Instruction *, 8> InstrsToErase;
249 // Map the block to reversed postorder traversal number. It is used to
250 // find back edge easily.
253 // This is set 'true' initially and also when new blocks have been added to
254 // the function being analyzed. This boolean is used to control the updating
255 // of BlockRPONumber prior to accessing the contents of BlockRPONumber.
256 bool InvalidBlockRPONumbers = true;
258 using LoadDepVect = SmallVector<NonLocalDepResult, 64>;
259 using AvailValInBlkVect = SmallVector<gvn::AvailableValueInBlock, 64>;
260 using UnavailBlkVect = SmallVector<BasicBlock *, 64>;
262 bool runImpl(Function &F, AssumptionCache &RunAC, DominatorTree &RunDT,
263 const TargetLibraryInfo &RunTLI, AAResults &RunAA,
265 OptimizationRemarkEmitter *ORE, MemorySSA *MSSA = nullptr);
267 /// Push a new Value to the LeaderTable onto the list for its value number.
268 void addToLeaderTable(uint32_t N, Value *V, const BasicBlock *BB) {
269 LeaderTableEntry &Curr = LeaderTable[N];
270 if (!Curr.Val) {
271 Curr.Val = V;
272 Curr.BB = BB;
273 return;
274 }
276 LeaderTableEntry *Node = TableAllocator.Allocate<LeaderTableEntry>();
277 Node->Val = V;
278 Node->BB = BB;
279 Node->Next = Curr.Next;
280 Curr.Next = Node;
281 }
283 /// Scan the list of values corresponding to a given
284 /// value number, and remove the given instruction if encountered.
285 void removeFromLeaderTable(uint32_t N, Instruction *I, BasicBlock *BB) {
286 LeaderTableEntry *Prev = nullptr;
287 LeaderTableEntry *Curr = &LeaderTable[N];
289 while (Curr && (Curr->Val != I || Curr->BB != BB)) {
290 Prev = Curr;
291 Curr = Curr->Next;
292 }
294 if (!Curr)
295 return;
297 if (Prev) {
298 Prev->Next = Curr->Next;
299 } else {
300 if (!Curr->Next) {
301 Curr->Val = nullptr;
302 Curr->BB = nullptr;
303 } else {
304 LeaderTableEntry *Next = Curr->Next;
305 Curr->Val = Next->Val;
306 Curr->BB = Next->BB;
307 Curr->Next = Next->Next;
308 }
309 }
310 }
312 // List of critical edges to be split between iterations.
313 SmallVector<std::pair<Instruction *, unsigned>, 4> toSplit;
315 // Helper functions of redundant load elimination
316 bool processLoad(LoadInst *L);
317 bool processNonLocalLoad(LoadInst *L);
318 bool processAssumeIntrinsic(AssumeInst *II);
320 /// Given a local dependency (Def or Clobber) determine if a value is
321 /// available for the load.
322 std::optional<gvn::AvailableValue>
323 AnalyzeLoadAvailability(LoadInst *Load, MemDepResult DepInfo, Value *Address);
325 /// Given a list of non-local dependencies, determine if a value is
326 /// available for the load in each specified block. If it is, add it to
327 /// ValuesPerBlock. If not, add it to UnavailableBlocks.
328 void AnalyzeLoadAvailability(LoadInst *Load, LoadDepVect &Deps,
329 AvailValInBlkVect &ValuesPerBlock,
330 UnavailBlkVect &UnavailableBlocks);
332 /// Given a critical edge from Pred to LoadBB, find a load instruction
333 /// which is identical to Load from another successor of Pred.
334 LoadInst *findLoadToHoistIntoPred(BasicBlock *Pred, BasicBlock *LoadBB,
335 LoadInst *Load);
337 bool PerformLoadPRE(LoadInst *Load, AvailValInBlkVect &ValuesPerBlock,
338 UnavailBlkVect &UnavailableBlocks);
340 /// Try to replace a load which executes on each loop iteraiton with Phi
341 /// translation of load in preheader and load(s) in conditionally executed
342 /// paths.
343 bool performLoopLoadPRE(LoadInst *Load, AvailValInBlkVect &ValuesPerBlock,
344 UnavailBlkVect &UnavailableBlocks);
346 /// Eliminates partially redundant \p Load, replacing it with \p
347 /// AvailableLoads (connected by Phis if needed).
348 void eliminatePartiallyRedundantLoad(
349 LoadInst *Load, AvailValInBlkVect &ValuesPerBlock,
350 MapVector<BasicBlock *, Value *> &AvailableLoads,
351 MapVector<BasicBlock *, LoadInst *> *CriticalEdgePredAndLoad);
353 // Other helper routines
354 bool processInstruction(Instruction *I);
355 bool processBlock(BasicBlock *BB);
356 void dump(DenseMap<uint32_t, Value *> &d) const;
357 bool iterateOnFunction(Function &F);
358 bool performPRE(Function &F);
359 bool performScalarPRE(Instruction *I);
360 bool performScalarPREInsertion(Instruction *Instr, BasicBlock *Pred,
361 BasicBlock *Curr, unsigned int ValNo);
362 Value *findLeader(const BasicBlock *BB, uint32_t num);
363 void cleanupGlobalSets();
364 void removeInstruction(Instruction *I);
365 void verifyRemoved(const Instruction *I) const;
366 bool splitCriticalEdges();
367 BasicBlock *splitCriticalEdges(BasicBlock *Pred, BasicBlock *Succ);
368 bool replaceOperandsForInBlockEquality(Instruction *I) const;
369 bool propagateEquality(Value *LHS, Value *RHS, const BasicBlockEdge &Root,
370 bool DominatesByEdge);
371 bool processFoldableCondBr(BranchInst *BI);
372 void addDeadBlock(BasicBlock *BB);
373 void assignValNumForDeadCode();
374 void assignBlockRPONumber(Function &F);
377/// Create a legacy GVN pass. This also allows parameterizing whether or not
378/// MemDep is enabled.
379FunctionPass *createGVNPass(bool NoMemDepAnalysis = false);
381/// A simple and fast domtree-based GVN pass to hoist common expressions
382/// from sibling branches.
383struct GVNHoistPass : PassInfoMixin<GVNHoistPass> {
384 /// Run the pass over the function.
388/// Uses an "inverted" value numbering to decide the similarity of
389/// expressions and sinks similar expressions into successors.
390struct GVNSinkPass : PassInfoMixin<GVNSinkPass> {
391 /// Run the pass over the function.
395} // end namespace llvm
This file defines the BumpPtrAllocator interface.
static GCRegistry::Add< ErlangGC > A("erlang", "erlang-compatible garbage collector")
static GCRegistry::Add< StatepointGC > D("statepoint-example", "an example strategy for statepoint")
Definition: Compiler.h:131
This file defines the DenseMap class.
early cse Early CSE w MemorySSA
Definition: EarlyCSE.cpp:1948
Hexagon Common GEP
static LVOptions Options
Definition: LVOptions.cpp:25
#define F(x, y, z)
Definition: MD5.cpp:55
#define I(x, y, z)
Definition: MD5.cpp:58
This file implements a map that provides insertion order iteration.
ppc ctr loops PowerPC CTR Loops Verify
This header defines various interfaces for pass management in LLVM.
raw_pwrite_stream & OS
This file implements a set that has insertion order iteration characteristics.
This file defines the SmallVector class.
Value * RHS
Value * LHS
A container for analyses that lazily runs them and caches their results.
Definition: PassManager.h:348
A cache of @llvm.assume calls within a function.
LLVM Basic Block Representation.
Definition: BasicBlock.h:60
Allocate memory in an ever growing pool, as if by bump-pointer.
Definition: Allocator.h:66
LLVM_ATTRIBUTE_RETURNS_NONNULL void * Allocate(size_t Size, Align Alignment)
Allocate space at the specified alignment.
Definition: Allocator.h:148
This class represents a function call, abstracting a target machine's calling convention.
This enumeration lists the possible predicates for CmpInst subclasses.
Definition: InstrTypes.h:780
Concrete subclass of DominatorTreeBase that is used to compute a normal dominator tree.
Definition: Dominators.h:162
This instruction extracts a struct member or array element value from an aggregate value.
This class holds the mapping between values and value numbers.
Definition: GVN.h:151
ValueTable(ValueTable &&Arg)
uint32_t lookupOrAddCmp(unsigned Opcode, CmpInst::Predicate Pred, Value *LHS, Value *RHS)
Returns the value number of the given comparison, assigning it a new number if it did not have one be...
Definition: GVN.cpp:692
uint32_t getNextUnusedValueNumber()
Definition: GVN.h:213
uint32_t lookupOrAdd(Value *V)
lookup_or_add - Returns the value number for the specified value, assigning it a new number if it did...
Definition: GVN.cpp:600
uint32_t lookup(Value *V, bool Verify=true) const
Returns the value number of the specified value.
Definition: GVN.cpp:679
ValueTable & operator=(const ValueTable &Arg)
void setAliasAnalysis(AAResults *A)
Definition: GVN.h:209
void clear()
Remove all entries from the ValueTable.
Definition: GVN.cpp:700
bool exists(Value *V) const
Returns true if a value number exists for the specified value.
Definition: GVN.cpp:594
ValueTable(const ValueTable &Arg)
AAResults * getAliasAnalysis() const
Definition: GVN.h:210
uint32_t phiTranslate(const BasicBlock *BB, const BasicBlock *PhiBlock, uint32_t Num, GVNPass &Gvn)
Wrap phiTranslateImpl to provide caching functionality.
Definition: GVN.cpp:2211
void setMemDep(MemoryDependenceResults *M)
Definition: GVN.h:211
void erase(Value *v)
Remove a value from the value numbering.
Definition: GVN.cpp:712
void add(Value *V, uint32_t num)
add - Insert a value into the table with a specified value number.
Definition: GVN.cpp:463
void setDomTree(DominatorTree *D)
Definition: GVN.h:212
void eraseTranslateCacheEntry(uint32_t Num, const BasicBlock &CurrBlock)
Erase stale entry from phiTranslate cache so phiTranslate can be computed again.
Definition: GVN.cpp:2315
void verifyRemoved(const Value *) const
verifyRemoved - Verify that the value is removed from all internal data structures.
Definition: GVN.cpp:722
The core GVN pass object.
Definition: GVN.h:117
bool isPREEnabled() const
Definition: GVN.cpp:731
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM)
Run the pass over the function.
Definition: GVN.cpp:752
AAResults * getAliasAnalysis() const
Definition: GVN.h:139
bool isLoadPREEnabled() const
Definition: GVN.cpp:735
GVNPass(GVNOptions Options={})
Definition: GVN.h:123
void printPipeline(raw_ostream &OS, function_ref< StringRef(StringRef)> MapClassName2PassName)
Definition: GVN.cpp:779
DominatorTree & getDominatorTree() const
Definition: GVN.h:138
bool isLoadInLoopPREEnabled() const
Definition: GVN.cpp:739
bool isLoadPRESplitBackedgeEnabled() const
Definition: GVN.cpp:743
void markInstructionForDeletion(Instruction *I)
This removes the specified instruction from our various maps and marks it for deletion.
Definition: GVN.h:133
bool isMemDepEnabled() const
Definition: GVN.cpp:748
MemoryDependenceResults & getMemDep() const
Definition: GVN.h:140
an instruction for type-safe pointer arithmetic to access elements of arrays and structs
Definition: Instructions.h:949
This class allows to keep track on instructions with implicit control flow.
Provides a lazy, caching interface for making common memory aliasing information queries,...
Encapsulates MemorySSA, including all data associated with memory accesses.
Definition: MemorySSA.h:700
The optimization diagnostic interface.
A set of analyses that are preserved following a run of a transformation pass.
Definition: Analysis.h:109
A vector that has set insertion semantics.
Definition: SetVector.h:57
void push_back(const T &Elt)
Definition: SmallVector.h:426
This is a 'vector' (really, a variable-sized array), optimized for the case when the array is small.
Definition: SmallVector.h:1209
Provides information about what library functions are available for the current target.
LLVM Value Representation.
Definition: Value.h:74
@ C
The default llvm calling convention, compatible with C.
Definition: CallingConv.h:34
@ BasicBlock
Various leaf nodes.
Definition: ISDOpcodes.h:71
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
AnalysisManager< Function > FunctionAnalysisManager
Convenience typedef for the Function analysis manager.
Definition: PassManager.h:637
FunctionPass * createGVNPass(bool NoMemDepAnalysis=false)
Create a legacy GVN pass.
Definition: GVN.cpp:3336
#define N
An information struct used to provide DenseMap with the various necessary components for a given valu...
Definition: DenseMapInfo.h:50
A simple and fast domtree-based GVN pass to hoist common expressions from sibling branches.
Definition: GVN.h:383
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM)
Run the pass over the function.
Definition: GVNHoist.cpp:1208
A set of parameters to control various transforms performed by GVN pass.
Definition: GVN.h:74
GVNOptions & setLoadPRE(bool LoadPRE)
Enables or disables PRE of loads in GVN.
Definition: GVN.h:90
std::optional< bool > AllowLoadPRESplitBackedge
Definition: GVN.h:78
GVNOptions & setPRE(bool PRE)
Enables or disables PRE in GVN.
Definition: GVN.h:84
GVNOptions & setLoadInLoopPRE(bool LoadInLoopPRE)
Definition: GVN.h:95
std::optional< bool > AllowPRE
Definition: GVN.h:75
std::optional< bool > AllowLoadInLoopPRE
Definition: GVN.h:77
std::optional< bool > AllowMemDep
Definition: GVN.h:79
GVNOptions & setMemDep(bool MemDep)
Enables or disables use of MemDepAnalysis.
Definition: GVN.h:107
std::optional< bool > AllowLoadPRE
Definition: GVN.h:76
GVNOptions & setLoadPRESplitBackedge(bool LoadPRESplitBackedge)
Enables or disables PRE of loads in GVN.
Definition: GVN.h:101
Uses an "inverted" value numbering to decide the similarity of expressions and sinks similar expressi...
Definition: GVN.h:390
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM)
Run the pass over the function.
Definition: GVNSink.cpp:889
A CRTP mix-in to automatically provide informational APIs needed for passes.
Definition: PassManager.h:91
A MapVector that performs no allocations if smaller than a certain size.
Definition: MapVector.h:254
Represents an AvailableValue which can be rematerialized at the end of the associated BasicBlock.
Definition: GVN.cpp:287
Represents a particular available value that we know how to materialize.
Definition: GVN.cpp:190