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//===- JumpThreading.h - thread control through conditional BBs -*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
/// \file
/// See the comments on JumpThreadingPass.
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Analysis/BlockFrequencyInfo.h"
#include "llvm/Analysis/BranchProbabilityInfo.h"
#include "llvm/Analysis/DomTreeUpdater.h"
#include "llvm/IR/ValueHandle.h"
#include <optional>
#include <utility>
namespace llvm {
class AAResults;
class BasicBlock;
class BinaryOperator;
class BranchInst;
class CmpInst;
class Constant;
class Function;
class Instruction;
class IntrinsicInst;
class LazyValueInfo;
class LoadInst;
class PHINode;
class SelectInst;
class SwitchInst;
class TargetLibraryInfo;
class TargetTransformInfo;
class Value;
/// A private "module" namespace for types and utilities used by
/// JumpThreading.
/// These are implementation details and should not be used by clients.
namespace jumpthreading {
// These are at global scope so static functions can use them too.
using PredValueInfo = SmallVectorImpl<std::pair<Constant *, BasicBlock *>>;
using PredValueInfoTy = SmallVector<std::pair<Constant *, BasicBlock *>, 8>;
// This is used to keep track of what kind of constant we're currently hoping
// to find.
enum ConstantPreference { WantInteger, WantBlockAddress };
} // end namespace jumpthreading
/// This pass performs 'jump threading', which looks at blocks that have
/// multiple predecessors and multiple successors. If one or more of the
/// predecessors of the block can be proven to always jump to one of the
/// successors, we forward the edge from the predecessor to the successor by
/// duplicating the contents of this block.
/// An example of when this can occur is code like this:
/// if () { ...
/// X = 4;
/// }
/// if (X < 3) {
/// In this case, the unconditional branch at the end of the first if can be
/// revectored to the false side of the second if.
class JumpThreadingPass : public PassInfoMixin<JumpThreadingPass> {
Function *F = nullptr;
FunctionAnalysisManager *FAM = nullptr;
TargetLibraryInfo *TLI = nullptr;
TargetTransformInfo *TTI = nullptr;
LazyValueInfo *LVI = nullptr;
AAResults *AA = nullptr;
std::unique_ptr<DomTreeUpdater> DTU;
std::optional<BlockFrequencyInfo *> BFI;
std::optional<BranchProbabilityInfo *> BPI;
bool ChangedSinceLastAnalysisUpdate = false;
bool HasGuards = false;
SmallPtrSet<const BasicBlock *, 16> LoopHeaders;
SmallSet<AssertingVH<const BasicBlock>, 16> LoopHeaders;
unsigned BBDupThreshold;
unsigned DefaultBBDupThreshold;
JumpThreadingPass(int T = -1);
// Glue for old PM.
bool runImpl(Function &F, FunctionAnalysisManager *FAM,
TargetLibraryInfo *TLI, TargetTransformInfo *TTI,
LazyValueInfo *LVI, AAResults *AA,
std::unique_ptr<DomTreeUpdater> DTU,
std::optional<BlockFrequencyInfo *> BFI,
std::optional<BranchProbabilityInfo *> BPI);
PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
DomTreeUpdater *getDomTreeUpdater() const { return DTU.get(); }
void findLoopHeaders(Function &F);
bool processBlock(BasicBlock *BB);
bool maybeMergeBasicBlockIntoOnlyPred(BasicBlock *BB);
void updateSSA(BasicBlock *BB, BasicBlock *NewBB,
DenseMap<Instruction *, Value *> &ValueMapping);
DenseMap<Instruction *, Value *> cloneInstructions(BasicBlock::iterator BI,
BasicBlock::iterator BE,
BasicBlock *NewBB,
BasicBlock *PredBB);
bool tryThreadEdge(BasicBlock *BB,
const SmallVectorImpl<BasicBlock *> &PredBBs,
BasicBlock *SuccBB);
void threadEdge(BasicBlock *BB, const SmallVectorImpl<BasicBlock *> &PredBBs,
BasicBlock *SuccBB);
bool duplicateCondBranchOnPHIIntoPred(
BasicBlock *BB, const SmallVectorImpl<BasicBlock *> &PredBBs);
bool computeValueKnownInPredecessorsImpl(
Value *V, BasicBlock *BB, jumpthreading::PredValueInfo &Result,
jumpthreading::ConstantPreference Preference,
DenseSet<Value *> &RecursionSet, Instruction *CxtI = nullptr);
computeValueKnownInPredecessors(Value *V, BasicBlock *BB,
jumpthreading::PredValueInfo &Result,
jumpthreading::ConstantPreference Preference,
Instruction *CxtI = nullptr) {
DenseSet<Value *> RecursionSet;
return computeValueKnownInPredecessorsImpl(V, BB, Result, Preference,
RecursionSet, CxtI);
Constant *evaluateOnPredecessorEdge(BasicBlock *BB, BasicBlock *PredPredBB,
Value *cond);
bool maybethreadThroughTwoBasicBlocks(BasicBlock *BB, Value *Cond);
void threadThroughTwoBasicBlocks(BasicBlock *PredPredBB, BasicBlock *PredBB,
BasicBlock *BB, BasicBlock *SuccBB);
bool processThreadableEdges(Value *Cond, BasicBlock *BB,
jumpthreading::ConstantPreference Preference,
Instruction *CxtI = nullptr);
bool processBranchOnPHI(PHINode *PN);
bool processBranchOnXOR(BinaryOperator *BO);
bool processImpliedCondition(BasicBlock *BB);
bool simplifyPartiallyRedundantLoad(LoadInst *LI);
void unfoldSelectInstr(BasicBlock *Pred, BasicBlock *BB, SelectInst *SI,
PHINode *SIUse, unsigned Idx);
bool tryToUnfoldSelect(CmpInst *CondCmp, BasicBlock *BB);
bool tryToUnfoldSelect(SwitchInst *SI, BasicBlock *BB);
bool tryToUnfoldSelectInCurrBB(BasicBlock *BB);
bool processGuards(BasicBlock *BB);
bool threadGuard(BasicBlock *BB, IntrinsicInst *Guard, BranchInst *BI);
BasicBlock *splitBlockPreds(BasicBlock *BB, ArrayRef<BasicBlock *> Preds,
const char *Suffix);
void updateBlockFreqAndEdgeWeight(BasicBlock *PredBB, BasicBlock *BB,
BasicBlock *NewBB, BasicBlock *SuccBB,
BlockFrequencyInfo *BFI,
BranchProbabilityInfo *BPI,
bool HasProfile);
/// Check if the block has profile metadata for its outgoing edges.
bool doesBlockHaveProfileData(BasicBlock *BB);
/// Returns analysis preserved by the pass.
PreservedAnalyses getPreservedAnalysis() const;
/// Helper function to run "external" analysis in the middle of JumpThreading.
/// It takes care of updating/invalidating other existing analysis
/// before/after running the "external" one.
template <typename AnalysisT>
typename AnalysisT::Result *runExternalAnalysis();
/// Returns an existing instance of BPI if any, otherwise nullptr. By
/// "existing" we mean either cached result provided by FunctionAnalysisManger
/// or created by preceding call to 'getOrCreateBPI'.
BranchProbabilityInfo *getBPI();
/// Returns an existing instance of BFI if any, otherwise nullptr. By
/// "existing" we mean either cached result provided by FunctionAnalysisManger
/// or created by preceding call to 'getOrCreateBFI'.
BlockFrequencyInfo *getBFI();
/// Returns an existing instance of BPI if any, otherwise:
/// if 'HasProfile' is true creates new instance through
/// FunctionAnalysisManager, otherwise nullptr.
BranchProbabilityInfo *getOrCreateBPI(bool Force = false);
/// Returns an existing instance of BFI if any, otherwise:
/// if 'HasProfile' is true creates new instance through
/// FunctionAnalysisManager, otherwise nullptr.
BlockFrequencyInfo *getOrCreateBFI(bool Force = false);
} // end namespace llvm