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//===- JumpThreading.h - thread control through conditional BBs -*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
/// \file
/// See the comments on JumpThreadingPass.
///
//===----------------------------------------------------------------------===//
#ifndef LLVM_TRANSFORMS_SCALAR_JUMPTHREADING_H
#define LLVM_TRANSFORMS_SCALAR_JUMPTHREADING_H
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/Analysis/BlockFrequencyInfo.h"
#include "llvm/Analysis/BlockFrequencyInfoImpl.h"
#include "llvm/Analysis/BranchProbabilityInfo.h"
#include "llvm/Analysis/LazyValueInfo.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/ValueHandle.h"
namespace llvm {
/// 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.
typedef SmallVectorImpl<std::pair<Constant *, BasicBlock *>> PredValueInfo;
typedef SmallVector<std::pair<Constant *, BasicBlock *>, 8> PredValueInfoTy;
// This is used to keep track of what kind of constant we're currently hoping
// to find.
enum ConstantPreference { WantInteger, WantBlockAddress };
}
/// 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> {
TargetLibraryInfo *TLI;
LazyValueInfo *LVI;
std::unique_ptr<BlockFrequencyInfo> BFI;
std::unique_ptr<BranchProbabilityInfo> BPI;
bool HasProfileData = false;
#ifdef NDEBUG
SmallPtrSet<const BasicBlock *, 16> LoopHeaders;
#else
SmallSet<AssertingVH<const BasicBlock>, 16> LoopHeaders;
#endif
DenseSet<std::pair<Value *, BasicBlock *>> RecursionSet;
unsigned BBDupThreshold;
// RAII helper for updating the recursion stack.
struct RecursionSetRemover {
DenseSet<std::pair<Value *, BasicBlock *>> &TheSet;
std::pair<Value *, BasicBlock *> ThePair;
RecursionSetRemover(DenseSet<std::pair<Value *, BasicBlock *>> &S,
std::pair<Value *, BasicBlock *> P)
: TheSet(S), ThePair(P) {}
~RecursionSetRemover() { TheSet.erase(ThePair); }
};
public:
JumpThreadingPass(int T = -1);
// Hack for MSVC 2013 which seems like it can't synthesize this.
JumpThreadingPass(JumpThreadingPass &&Other)
: TLI(Other.TLI), LVI(Other.LVI), BFI(std::move(Other.BFI)),
BPI(std::move(Other.BPI)), HasProfileData(Other.HasProfileData),
LoopHeaders(std::move(Other.LoopHeaders)),
RecursionSet(std::move(Other.RecursionSet)),
BBDupThreshold(Other.BBDupThreshold) {}
// Glue for old PM.
bool runImpl(Function &F, TargetLibraryInfo *TLI_, LazyValueInfo *LVI_,
bool HasProfileData_, std::unique_ptr<BlockFrequencyInfo> BFI_,
std::unique_ptr<BranchProbabilityInfo> BPI_);
PreservedAnalyses run(Function &F, AnalysisManager<Function> &AM);
void releaseMemory() {
BFI.reset();
BPI.reset();
}
void FindLoopHeaders(Function &F);
bool ProcessBlock(BasicBlock *BB);
bool ThreadEdge(BasicBlock *BB, const SmallVectorImpl<BasicBlock *> &PredBBs,
BasicBlock *SuccBB);
bool DuplicateCondBranchOnPHIIntoPred(
BasicBlock *BB, const SmallVectorImpl<BasicBlock *> &PredBBs);
bool
ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,
jumpthreading::PredValueInfo &Result,
jumpthreading::ConstantPreference Preference,
Instruction *CxtI = nullptr);
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);
bool TryToUnfoldSelect(CmpInst *CondCmp, BasicBlock *BB);
bool TryToUnfoldSelectInCurrBB(BasicBlock *BB);
private:
BasicBlock *SplitBlockPreds(BasicBlock *BB, ArrayRef<BasicBlock *> Preds,
const char *Suffix);
void UpdateBlockFreqAndEdgeWeight(BasicBlock *PredBB, BasicBlock *BB,
BasicBlock *NewBB, BasicBlock *SuccBB);
};
} // end namespace llvm
#endif
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