llvm-project/llvm/lib/CodeGen/BranchFolding.h

//===-- BranchFolding.h - Fold machine code branch instructions -*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_LIB_CODEGEN_BRANCHFOLDING_H
#define LLVM_LIB_CODEGEN_BRANCHFOLDING_H

#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/CodeGen/LivePhysRegs.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/Support/BlockFrequency.h"
#include <vector>

namespace llvm {
  class MachineBlockFrequencyInfo;
  class MachineBranchProbabilityInfo;
  class MachineFunction;
  class MachineModuleInfo;
  class MachineLoopInfo;
  class TargetInstrInfo;
  class TargetRegisterInfo;

  class LLVM_LIBRARY_VISIBILITY BranchFolder {
  public:
    class MBFIWrapper;

    explicit BranchFolder(bool defaultEnableTailMerge,
                          bool CommonHoist,
                          MBFIWrapper &MBFI,
                          const MachineBranchProbabilityInfo &MBPI,
                          // Min tail length to merge. Defaults to commandline
                          // flag. Ignored for optsize.
                          unsigned MinCommonTailLength = 0);

    bool OptimizeFunction(MachineFunction &MF, const TargetInstrInfo *tii,
                          const TargetRegisterInfo *tri, MachineModuleInfo *mmi,
                          MachineLoopInfo *mli = nullptr,
                          bool AfterPlacement = false);

  private:
    class MergePotentialsElt {
      unsigned Hash;
      MachineBasicBlock *Block;
    public:
      MergePotentialsElt(unsigned h, MachineBasicBlock *b)
        : Hash(h), Block(b) {}

      unsigned getHash() const { return Hash; }
      MachineBasicBlock *getBlock() const { return Block; }

      void setBlock(MachineBasicBlock *MBB) {
        Block = MBB;
      }

      bool operator<(const MergePotentialsElt &) const;
    };
    typedef std::vector<MergePotentialsElt>::iterator MPIterator;
    std::vector<MergePotentialsElt> MergePotentials;
    SmallPtrSet<const MachineBasicBlock*, 2> TriedMerging;
    DenseMap<const MachineBasicBlock *, int> FuncletMembership;

    class SameTailElt {
      MPIterator MPIter;
      MachineBasicBlock::iterator TailStartPos;
    public:
      SameTailElt(MPIterator mp, MachineBasicBlock::iterator tsp)
        : MPIter(mp), TailStartPos(tsp) {}

      MPIterator getMPIter() const {
        return MPIter;
      }
      MergePotentialsElt &getMergePotentialsElt() const {
        return *getMPIter();
      }
      MachineBasicBlock::iterator getTailStartPos() const {
        return TailStartPos;
      }
      unsigned getHash() const {
        return getMergePotentialsElt().getHash();
      }
      MachineBasicBlock *getBlock() const {
        return getMergePotentialsElt().getBlock();
      }
      bool tailIsWholeBlock() const {
        return TailStartPos == getBlock()->begin();
      }

      void setBlock(MachineBasicBlock *MBB) {
        getMergePotentialsElt().setBlock(MBB);
      }
      void setTailStartPos(MachineBasicBlock::iterator Pos) {
        TailStartPos = Pos;
      }
    };
    std::vector<SameTailElt> SameTails;

    bool AfterBlockPlacement;
    bool EnableTailMerge;
    bool EnableHoistCommonCode;
    bool UpdateLiveIns;
    unsigned MinCommonTailLength;
    const TargetInstrInfo *TII;
    const TargetRegisterInfo *TRI;
    MachineModuleInfo *MMI;
    MachineLoopInfo *MLI;
    LivePhysRegs LiveRegs;

  public:
    /// \brief This class keeps track of branch frequencies of newly created
    /// blocks and tail-merged blocks.
    class MBFIWrapper {
    public:
      MBFIWrapper(const MachineBlockFrequencyInfo &I) : MBFI(I) {}
      BlockFrequency getBlockFreq(const MachineBasicBlock *MBB) const;
      void setBlockFreq(const MachineBasicBlock *MBB, BlockFrequency F);
      raw_ostream &printBlockFreq(raw_ostream &OS,
                                  const MachineBasicBlock *MBB) const;
      raw_ostream &printBlockFreq(raw_ostream &OS,
                                  const BlockFrequency Freq) const;

    private:
      const MachineBlockFrequencyInfo &MBFI;
      DenseMap<const MachineBasicBlock *, BlockFrequency> MergedBBFreq;
    };

  private:
    MBFIWrapper &MBBFreqInfo;
    const MachineBranchProbabilityInfo &MBPI;

    bool TailMergeBlocks(MachineFunction &MF);
    bool TryTailMergeBlocks(MachineBasicBlock* SuccBB,
                       MachineBasicBlock* PredBB,
                       unsigned MinCommonTailLength);
    void setCommonTailEdgeWeights(MachineBasicBlock &TailMBB);
    void ReplaceTailWithBranchTo(MachineBasicBlock::iterator OldInst,
                                 MachineBasicBlock *NewDest);
    MachineBasicBlock *SplitMBBAt(MachineBasicBlock &CurMBB,
                                  MachineBasicBlock::iterator BBI1,
                                  const BasicBlock *BB);
    unsigned ComputeSameTails(unsigned CurHash, unsigned minCommonTailLength,
                              MachineBasicBlock *SuccBB,
                              MachineBasicBlock *PredBB);
    void RemoveBlocksWithHash(unsigned CurHash, MachineBasicBlock* SuccBB,
                                                MachineBasicBlock* PredBB);
    bool CreateCommonTailOnlyBlock(MachineBasicBlock *&PredBB,
                                   MachineBasicBlock *SuccBB,
                                   unsigned maxCommonTailLength,
                                   unsigned &commonTailIndex);

    bool OptimizeBranches(MachineFunction &MF);
    bool OptimizeBlock(MachineBasicBlock *MBB);
    void RemoveDeadBlock(MachineBasicBlock *MBB);

    bool HoistCommonCode(MachineFunction &MF);
    bool HoistCommonCodeInSuccs(MachineBasicBlock *MBB);
  };
}

#endif /* LLVM_CODEGEN_BRANCHFOLDING_HPP */