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ac54d0066c
Summary: These are good candidates for jump threading. This enables later opts (such as InstCombine) to combine instructions from the selects with instructions out of the selects. SimplifyCFG will fold the select again if unfolding wasn't worth it. Patch by James Molloy and Pablo Barrio. Reviewers: rengolin, haicheng, sebpop Subscribers: jojo, jmolloy, llvm-commits Differential Revision: https://reviews.llvm.org/D26391 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@286236 91177308-0d34-0410-b5e6-96231b3b80d8
139 lines
4.9 KiB
C++
139 lines
4.9 KiB
C++
//===- JumpThreading.h - thread control through conditional BBs -*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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/// \file
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/// See the comments on JumpThreadingPass.
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///
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_TRANSFORMS_SCALAR_JUMPTHREADING_H
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#define LLVM_TRANSFORMS_SCALAR_JUMPTHREADING_H
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#include "llvm/ADT/DenseSet.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/SmallSet.h"
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#include "llvm/Analysis/BlockFrequencyInfo.h"
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#include "llvm/Analysis/BlockFrequencyInfoImpl.h"
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#include "llvm/Analysis/BranchProbabilityInfo.h"
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#include "llvm/Analysis/LazyValueInfo.h"
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#include "llvm/Analysis/TargetLibraryInfo.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/ValueHandle.h"
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namespace llvm {
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/// A private "module" namespace for types and utilities used by
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/// JumpThreading.
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/// These are implementation details and should not be used by clients.
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namespace jumpthreading {
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// These are at global scope so static functions can use them too.
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typedef SmallVectorImpl<std::pair<Constant *, BasicBlock *>> PredValueInfo;
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typedef SmallVector<std::pair<Constant *, BasicBlock *>, 8> PredValueInfoTy;
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// This is used to keep track of what kind of constant we're currently hoping
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// to find.
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enum ConstantPreference { WantInteger, WantBlockAddress };
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}
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/// This pass performs 'jump threading', which looks at blocks that have
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/// multiple predecessors and multiple successors. If one or more of the
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/// predecessors of the block can be proven to always jump to one of the
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/// successors, we forward the edge from the predecessor to the successor by
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/// duplicating the contents of this block.
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///
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/// An example of when this can occur is code like this:
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///
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/// if () { ...
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/// X = 4;
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/// }
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/// if (X < 3) {
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///
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/// In this case, the unconditional branch at the end of the first if can be
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/// revectored to the false side of the second if.
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///
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class JumpThreadingPass : public PassInfoMixin<JumpThreadingPass> {
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TargetLibraryInfo *TLI;
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LazyValueInfo *LVI;
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std::unique_ptr<BlockFrequencyInfo> BFI;
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std::unique_ptr<BranchProbabilityInfo> BPI;
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bool HasProfileData = false;
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#ifdef NDEBUG
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SmallPtrSet<const BasicBlock *, 16> LoopHeaders;
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#else
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SmallSet<AssertingVH<const BasicBlock>, 16> LoopHeaders;
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#endif
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DenseSet<std::pair<Value *, BasicBlock *>> RecursionSet;
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unsigned BBDupThreshold;
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// RAII helper for updating the recursion stack.
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struct RecursionSetRemover {
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DenseSet<std::pair<Value *, BasicBlock *>> &TheSet;
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std::pair<Value *, BasicBlock *> ThePair;
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RecursionSetRemover(DenseSet<std::pair<Value *, BasicBlock *>> &S,
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std::pair<Value *, BasicBlock *> P)
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: TheSet(S), ThePair(P) {}
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~RecursionSetRemover() { TheSet.erase(ThePair); }
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};
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public:
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JumpThreadingPass(int T = -1);
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// Glue for old PM.
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bool runImpl(Function &F, TargetLibraryInfo *TLI_, LazyValueInfo *LVI_,
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bool HasProfileData_, std::unique_ptr<BlockFrequencyInfo> BFI_,
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std::unique_ptr<BranchProbabilityInfo> BPI_);
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PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
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void releaseMemory() {
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BFI.reset();
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BPI.reset();
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}
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void FindLoopHeaders(Function &F);
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bool ProcessBlock(BasicBlock *BB);
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bool ThreadEdge(BasicBlock *BB, const SmallVectorImpl<BasicBlock *> &PredBBs,
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BasicBlock *SuccBB);
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bool DuplicateCondBranchOnPHIIntoPred(
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BasicBlock *BB, const SmallVectorImpl<BasicBlock *> &PredBBs);
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bool
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ComputeValueKnownInPredecessors(Value *V, BasicBlock *BB,
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jumpthreading::PredValueInfo &Result,
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jumpthreading::ConstantPreference Preference,
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Instruction *CxtI = nullptr);
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bool ProcessThreadableEdges(Value *Cond, BasicBlock *BB,
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jumpthreading::ConstantPreference Preference,
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Instruction *CxtI = nullptr);
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bool ProcessBranchOnPHI(PHINode *PN);
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bool ProcessBranchOnXOR(BinaryOperator *BO);
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bool ProcessImpliedCondition(BasicBlock *BB);
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bool SimplifyPartiallyRedundantLoad(LoadInst *LI);
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bool TryToUnfoldSelect(CmpInst *CondCmp, BasicBlock *BB);
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bool TryToUnfoldSelectInCurrBB(BasicBlock *BB);
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private:
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BasicBlock *SplitBlockPreds(BasicBlock *BB, ArrayRef<BasicBlock *> Preds,
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const char *Suffix);
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void UpdateBlockFreqAndEdgeWeight(BasicBlock *PredBB, BasicBlock *BB,
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BasicBlock *NewBB, BasicBlock *SuccBB);
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/// Check if the block has profile metadata for its outgoing edges.
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bool doesBlockHaveProfileData(BasicBlock *BB);
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SelectInst *getSelectFedByPhi(PHINode *PN);
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void expandSelect(SelectInst *SI);
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};
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} // end namespace llvm
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#endif
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