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//===- GVN.h - Eliminate redundant values and loads -------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
/// \file
/// This file provides the interface for LLVM's Global Value Numbering pass
/// which eliminates fully redundant instructions. It also does somewhat Ad-Hoc
/// PRE and dead load elimination.
///
//===----------------------------------------------------------------------===//
#ifndef LLVM_TRANSFORMS_SCALAR_GVN_H
#define LLVM_TRANSFORMS_SCALAR_GVN_H
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/Compiler.h"
#include <cstdint>
#include <optional>
#include <utility>
#include <vector>
namespace llvm {
class AAResults;
class AssumeInst;
class AssumptionCache;
class BasicBlock;
class BranchInst;
class CallInst;
class ExtractValueInst;
class Function;
class FunctionPass;
class GetElementPtrInst;
class ImplicitControlFlowTracking;
class LoadInst;
class LoopInfo;
class MemDepResult;
class MemoryDependenceResults;
class MemorySSA;
class MemorySSAUpdater;
class NonLocalDepResult;
class OptimizationRemarkEmitter;
class PHINode;
class TargetLibraryInfo;
class Value;
/// A private "module" namespace for types and utilities used by GVN. These
/// are implementation details and should not be used by clients.
namespace LLVM_LIBRARY_VISIBILITY gvn {
struct AvailableValue;
struct AvailableValueInBlock;
class GVNLegacyPass;
} // end namespace gvn
/// A set of parameters to control various transforms performed by GVN pass.
// Each of the optional boolean parameters can be set to:
/// true - enabling the transformation.
/// false - disabling the transformation.
/// None - relying on a global default.
/// Intended use is to create a default object, modify parameters with
/// additional setters and then pass it to GVN.
struct GVNOptions {
std::optional<bool> AllowPRE;
std::optional<bool> AllowLoadPRE;
std::optional<bool> AllowLoadInLoopPRE;
std::optional<bool> AllowLoadPRESplitBackedge;
std::optional<bool> AllowMemDep;
GVNOptions() = default;
/// Enables or disables PRE in GVN.
GVNOptions &setPRE(bool PRE) {
AllowPRE = PRE;
return *this;
}
/// Enables or disables PRE of loads in GVN.
GVNOptions &setLoadPRE(bool LoadPRE) {
AllowLoadPRE = LoadPRE;
return *this;
}
GVNOptions &setLoadInLoopPRE(bool LoadInLoopPRE) {
AllowLoadInLoopPRE = LoadInLoopPRE;
return *this;
}
/// Enables or disables PRE of loads in GVN.
GVNOptions &setLoadPRESplitBackedge(bool LoadPRESplitBackedge) {
AllowLoadPRESplitBackedge = LoadPRESplitBackedge;
return *this;
}
/// Enables or disables use of MemDepAnalysis.
GVNOptions &setMemDep(bool MemDep) {
AllowMemDep = MemDep;
return *this;
}
};
/// The core GVN pass object.
///
/// FIXME: We should have a good summary of the GVN algorithm implemented by
/// this particular pass here.
class GVNPass : public PassInfoMixin<GVNPass> {
GVNOptions Options;
public:
struct Expression;
GVNPass(GVNOptions Options = {}) : Options(Options) {}
/// Run the pass over the function.
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
void printPipeline(raw_ostream &OS,
function_ref<StringRef(StringRef)> MapClassName2PassName);
/// This removes the specified instruction from
/// our various maps and marks it for deletion.
void markInstructionForDeletion(Instruction *I) {
VN.erase(I);
InstrsToErase.push_back(I);
}
DominatorTree &getDominatorTree() const { return *DT; }
AAResults *getAliasAnalysis() const { return VN.getAliasAnalysis(); }
MemoryDependenceResults &getMemDep() const { return *MD; }
bool isPREEnabled() const;
bool isLoadPREEnabled() const;
bool isLoadInLoopPREEnabled() const;
bool isLoadPRESplitBackedgeEnabled() const;
bool isMemDepEnabled() const;
/// This class holds the mapping between values and value numbers. It is used
/// as an efficient mechanism to determine the expression-wise equivalence of
/// two values.
class ValueTable {
DenseMap<Value *, uint32_t> valueNumbering;
DenseMap<Expression, uint32_t> expressionNumbering;
// Expressions is the vector of Expression. ExprIdx is the mapping from
// value number to the index of Expression in Expressions. We use it
// instead of a DenseMap because filling such mapping is faster than
// filling a DenseMap and the compile time is a little better.
uint32_t nextExprNumber = 0;
std::vector<Expression> Expressions;
std::vector<uint32_t> ExprIdx;
// Value number to PHINode mapping. Used for phi-translate in scalarpre.
DenseMap<uint32_t, PHINode *> NumberingPhi;
// Cache for phi-translate in scalarpre.
using PhiTranslateMap =
DenseMap<std::pair<uint32_t, const BasicBlock *>, uint32_t>;
PhiTranslateMap PhiTranslateTable;
AAResults *AA = nullptr;
MemoryDependenceResults *MD = nullptr;
DominatorTree *DT = nullptr;
uint32_t nextValueNumber = 1;
Expression createExpr(Instruction *I);
Expression createCmpExpr(unsigned Opcode, CmpInst::Predicate Predicate,
Value *LHS, Value *RHS);
Expression createExtractvalueExpr(ExtractValueInst *EI);
Expression createGEPExpr(GetElementPtrInst *GEP);
uint32_t lookupOrAddCall(CallInst *C);
uint32_t phiTranslateImpl(const BasicBlock *BB, const BasicBlock *PhiBlock,
uint32_t Num, GVNPass &Gvn);
bool areCallValsEqual(uint32_t Num, uint32_t NewNum, const BasicBlock *Pred,
const BasicBlock *PhiBlock, GVNPass &Gvn);
std::pair<uint32_t, bool> assignExpNewValueNum(Expression &exp);
bool areAllValsInBB(uint32_t num, const BasicBlock *BB, GVNPass &Gvn);
public:
ValueTable();
ValueTable(const ValueTable &Arg);
ValueTable(ValueTable &&Arg);
~ValueTable();
ValueTable &operator=(const ValueTable &Arg);
uint32_t lookupOrAdd(Value *V);
uint32_t lookup(Value *V, bool Verify = true) const;
uint32_t lookupOrAddCmp(unsigned Opcode, CmpInst::Predicate Pred,
Value *LHS, Value *RHS);
uint32_t phiTranslate(const BasicBlock *BB, const BasicBlock *PhiBlock,
uint32_t Num, GVNPass &Gvn);
void eraseTranslateCacheEntry(uint32_t Num, const BasicBlock &CurrBlock);
bool exists(Value *V) const;
void add(Value *V, uint32_t num);
void clear();
void erase(Value *v);
void setAliasAnalysis(AAResults *A) { AA = A; }
AAResults *getAliasAnalysis() const { return AA; }
void setMemDep(MemoryDependenceResults *M) { MD = M; }
void setDomTree(DominatorTree *D) { DT = D; }
uint32_t getNextUnusedValueNumber() { return nextValueNumber; }
void verifyRemoved(const Value *) const;
};
private:
friend class gvn::GVNLegacyPass;
friend struct DenseMapInfo<Expression>;
MemoryDependenceResults *MD = nullptr;
DominatorTree *DT = nullptr;
const TargetLibraryInfo *TLI = nullptr;
AssumptionCache *AC = nullptr;
SetVector<BasicBlock *> DeadBlocks;
OptimizationRemarkEmitter *ORE = nullptr;
ImplicitControlFlowTracking *ICF = nullptr;
LoopInfo *LI = nullptr;
MemorySSAUpdater *MSSAU = nullptr;
ValueTable VN;
/// A mapping from value numbers to lists of Value*'s that
/// have that value number. Use findLeader to query it.
class LeaderMap {
public:
struct LeaderTableEntry {
Value *Val;
const BasicBlock *BB;
};
private:
struct LeaderListNode {
LeaderTableEntry Entry;
LeaderListNode *Next;
};
DenseMap<uint32_t, LeaderListNode> NumToLeaders;
BumpPtrAllocator TableAllocator;
public:
class leader_iterator {
const LeaderListNode *Current;
public:
using iterator_category = std::forward_iterator_tag;
using value_type = const LeaderTableEntry;
using difference_type = std::ptrdiff_t;
using pointer = value_type *;
using reference = value_type &;
leader_iterator(const LeaderListNode *C) : Current(C) {}
leader_iterator &operator++() {
assert(Current && "Dereferenced end of leader list!");
Current = Current->Next;
return *this;
}
bool operator==(const leader_iterator &Other) const {
return Current == Other.Current;
}
bool operator!=(const leader_iterator &Other) const {
return Current != Other.Current;
}
reference operator*() const { return Current->Entry; }
};
iterator_range<leader_iterator> getLeaders(uint32_t N) {
auto I = NumToLeaders.find(N);
if (I == NumToLeaders.end()) {
return iterator_range(leader_iterator(nullptr),
leader_iterator(nullptr));
}
return iterator_range(leader_iterator(&I->second),
leader_iterator(nullptr));
}
void insert(uint32_t N, Value *V, const BasicBlock *BB);
void erase(uint32_t N, Instruction *I, const BasicBlock *BB);
void verifyRemoved(const Value *Inst) const;
void clear() {
NumToLeaders.clear();
TableAllocator.Reset();
}
};
LeaderMap LeaderTable;
// Block-local map of equivalent values to their leader, does not
// propagate to any successors. Entries added mid-block are applied
// to the remaining instructions in the block.
SmallMapVector<Value *, Value *, 4> ReplaceOperandsWithMap;
SmallVector<Instruction *, 8> InstrsToErase;
// Map the block to reversed postorder traversal number. It is used to
// find back edge easily.
DenseMap<AssertingVH<BasicBlock>, uint32_t> BlockRPONumber;
// This is set 'true' initially and also when new blocks have been added to
// the function being analyzed. This boolean is used to control the updating
// of BlockRPONumber prior to accessing the contents of BlockRPONumber.
bool InvalidBlockRPONumbers = true;
using LoadDepVect = SmallVector<NonLocalDepResult, 64>;
using AvailValInBlkVect = SmallVector<gvn::AvailableValueInBlock, 64>;
using UnavailBlkVect = SmallVector<BasicBlock *, 64>;
bool runImpl(Function &F, AssumptionCache &RunAC, DominatorTree &RunDT,
const TargetLibraryInfo &RunTLI, AAResults &RunAA,
MemoryDependenceResults *RunMD, LoopInfo &LI,
OptimizationRemarkEmitter *ORE, MemorySSA *MSSA = nullptr);
// List of critical edges to be split between iterations.
SmallVector<std::pair<Instruction *, unsigned>, 4> toSplit;
// Helper functions of redundant load elimination
bool processLoad(LoadInst *L);
bool processNonLocalLoad(LoadInst *L);
bool processAssumeIntrinsic(AssumeInst *II);
/// Given a local dependency (Def or Clobber) determine if a value is
/// available for the load.
std::optional<gvn::AvailableValue>
AnalyzeLoadAvailability(LoadInst *Load, MemDepResult DepInfo, Value *Address);
/// Given a list of non-local dependencies, determine if a value is
/// available for the load in each specified block. If it is, add it to
/// ValuesPerBlock. If not, add it to UnavailableBlocks.
void AnalyzeLoadAvailability(LoadInst *Load, LoadDepVect &Deps,
AvailValInBlkVect &ValuesPerBlock,
UnavailBlkVect &UnavailableBlocks);
/// Given a critical edge from Pred to LoadBB, find a load instruction
/// which is identical to Load from another successor of Pred.
LoadInst *findLoadToHoistIntoPred(BasicBlock *Pred, BasicBlock *LoadBB,
LoadInst *Load);
bool PerformLoadPRE(LoadInst *Load, AvailValInBlkVect &ValuesPerBlock,
UnavailBlkVect &UnavailableBlocks);
/// Try to replace a load which executes on each loop iteraiton with Phi
/// translation of load in preheader and load(s) in conditionally executed
/// paths.
bool performLoopLoadPRE(LoadInst *Load, AvailValInBlkVect &ValuesPerBlock,
UnavailBlkVect &UnavailableBlocks);
/// Eliminates partially redundant \p Load, replacing it with \p
/// AvailableLoads (connected by Phis if needed).
void eliminatePartiallyRedundantLoad(
LoadInst *Load, AvailValInBlkVect &ValuesPerBlock,
MapVector<BasicBlock *, Value *> &AvailableLoads,
MapVector<BasicBlock *, LoadInst *> *CriticalEdgePredAndLoad);
// Other helper routines
bool processInstruction(Instruction *I);
bool processBlock(BasicBlock *BB);
void dump(DenseMap<uint32_t, Value *> &d) const;
bool iterateOnFunction(Function &F);
bool performPRE(Function &F);
bool performScalarPRE(Instruction *I);
bool performScalarPREInsertion(Instruction *Instr, BasicBlock *Pred,
BasicBlock *Curr, unsigned int ValNo);
Value *findLeader(const BasicBlock *BB, uint32_t num);
void cleanupGlobalSets();
void removeInstruction(Instruction *I);
void verifyRemoved(const Instruction *I) const;
bool splitCriticalEdges();
BasicBlock *splitCriticalEdges(BasicBlock *Pred, BasicBlock *Succ);
bool replaceOperandsForInBlockEquality(Instruction *I) const;
bool propagateEquality(Value *LHS, Value *RHS, const BasicBlockEdge &Root,
bool DominatesByEdge);
bool processFoldableCondBr(BranchInst *BI);
void addDeadBlock(BasicBlock *BB);
void assignValNumForDeadCode();
void assignBlockRPONumber(Function &F);
};
/// Create a legacy GVN pass. This also allows parameterizing whether or not
/// MemDep is enabled.
FunctionPass *createGVNPass(bool NoMemDepAnalysis = false);
/// A simple and fast domtree-based GVN pass to hoist common expressions
/// from sibling branches.
struct GVNHoistPass : PassInfoMixin<GVNHoistPass> {
/// Run the pass over the function.
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
};
/// Uses an "inverted" value numbering to decide the similarity of
/// expressions and sinks similar expressions into successors.
struct GVNSinkPass : PassInfoMixin<GVNSinkPass> {
/// Run the pass over the function.
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
};
} // end namespace llvm
#endif // LLVM_TRANSFORMS_SCALAR_GVN_H
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