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external/llvm/lib/CodeGen/BranchFolding.h
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external/llvm/lib/CodeGen/BranchFolding.h
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//===- BranchFolding.h - Fold machine code branch instructions --*- 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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#ifndef LLVM_LIB_CODEGEN_BRANCHFOLDING_H
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#define LLVM_LIB_CODEGEN_BRANCHFOLDING_H
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/CodeGen/LivePhysRegs.h"
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#include "llvm/CodeGen/MachineBasicBlock.h"
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#include "llvm/Support/BlockFrequency.h"
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#include "llvm/Support/Compiler.h"
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#include <cstdint>
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#include <vector>
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namespace llvm {
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class BasicBlock;
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class MachineBlockFrequencyInfo;
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class MachineBranchProbabilityInfo;
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class MachineFunction;
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class MachineLoopInfo;
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class MachineModuleInfo;
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class MachineRegisterInfo;
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class raw_ostream;
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class TargetInstrInfo;
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class TargetRegisterInfo;
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class LLVM_LIBRARY_VISIBILITY BranchFolder {
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public:
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class MBFIWrapper;
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explicit BranchFolder(bool defaultEnableTailMerge,
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bool CommonHoist,
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MBFIWrapper &MBFI,
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const MachineBranchProbabilityInfo &MBPI,
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// Min tail length to merge. Defaults to commandline
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// flag. Ignored for optsize.
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unsigned MinCommonTailLength = 0);
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/// Perhaps branch folding, tail merging and other CFG optimizations on the
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/// given function. Block placement changes the layout and may create new
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/// tail merging opportunities.
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bool OptimizeFunction(MachineFunction &MF, const TargetInstrInfo *tii,
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const TargetRegisterInfo *tri, MachineModuleInfo *mmi,
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MachineLoopInfo *mli = nullptr,
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bool AfterPlacement = false);
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private:
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class MergePotentialsElt {
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unsigned Hash;
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MachineBasicBlock *Block;
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public:
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MergePotentialsElt(unsigned h, MachineBasicBlock *b)
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: Hash(h), Block(b) {}
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unsigned getHash() const { return Hash; }
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MachineBasicBlock *getBlock() const { return Block; }
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void setBlock(MachineBasicBlock *MBB) {
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Block = MBB;
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}
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bool operator<(const MergePotentialsElt &) const;
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};
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using MPIterator = std::vector<MergePotentialsElt>::iterator;
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std::vector<MergePotentialsElt> MergePotentials;
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SmallPtrSet<const MachineBasicBlock*, 2> TriedMerging;
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DenseMap<const MachineBasicBlock *, int> FuncletMembership;
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class SameTailElt {
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MPIterator MPIter;
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MachineBasicBlock::iterator TailStartPos;
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public:
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SameTailElt(MPIterator mp, MachineBasicBlock::iterator tsp)
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: MPIter(mp), TailStartPos(tsp) {}
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MPIterator getMPIter() const {
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return MPIter;
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}
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MergePotentialsElt &getMergePotentialsElt() const {
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return *getMPIter();
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}
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MachineBasicBlock::iterator getTailStartPos() const {
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return TailStartPos;
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}
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unsigned getHash() const {
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return getMergePotentialsElt().getHash();
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}
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MachineBasicBlock *getBlock() const {
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return getMergePotentialsElt().getBlock();
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}
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bool tailIsWholeBlock() const {
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return TailStartPos == getBlock()->begin();
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}
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void setBlock(MachineBasicBlock *MBB) {
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getMergePotentialsElt().setBlock(MBB);
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}
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void setTailStartPos(MachineBasicBlock::iterator Pos) {
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TailStartPos = Pos;
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}
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};
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std::vector<SameTailElt> SameTails;
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bool AfterBlockPlacement;
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bool EnableTailMerge;
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bool EnableHoistCommonCode;
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bool UpdateLiveIns;
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unsigned MinCommonTailLength;
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const TargetInstrInfo *TII;
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const MachineRegisterInfo *MRI;
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const TargetRegisterInfo *TRI;
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MachineModuleInfo *MMI;
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MachineLoopInfo *MLI;
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LivePhysRegs LiveRegs;
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public:
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/// \brief This class keeps track of branch frequencies of newly created
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/// blocks and tail-merged blocks.
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class MBFIWrapper {
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public:
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MBFIWrapper(const MachineBlockFrequencyInfo &I) : MBFI(I) {}
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BlockFrequency getBlockFreq(const MachineBasicBlock *MBB) const;
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void setBlockFreq(const MachineBasicBlock *MBB, BlockFrequency F);
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raw_ostream &printBlockFreq(raw_ostream &OS,
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const MachineBasicBlock *MBB) const;
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raw_ostream &printBlockFreq(raw_ostream &OS,
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const BlockFrequency Freq) const;
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void view(const Twine &Name, bool isSimple = true);
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uint64_t getEntryFreq() const;
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private:
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const MachineBlockFrequencyInfo &MBFI;
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DenseMap<const MachineBasicBlock *, BlockFrequency> MergedBBFreq;
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};
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private:
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MBFIWrapper &MBBFreqInfo;
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const MachineBranchProbabilityInfo &MBPI;
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bool TailMergeBlocks(MachineFunction &MF);
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bool TryTailMergeBlocks(MachineBasicBlock* SuccBB,
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MachineBasicBlock* PredBB,
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unsigned MinCommonTailLength);
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void setCommonTailEdgeWeights(MachineBasicBlock &TailMBB);
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/// Delete the instruction OldInst and everything after it, replacing it
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/// with an unconditional branch to NewDest.
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void replaceTailWithBranchTo(MachineBasicBlock::iterator OldInst,
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MachineBasicBlock &NewDest);
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/// Given a machine basic block and an iterator into it, split the MBB so
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/// that the part before the iterator falls into the part starting at the
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/// iterator. This returns the new MBB.
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MachineBasicBlock *SplitMBBAt(MachineBasicBlock &CurMBB,
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MachineBasicBlock::iterator BBI1,
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const BasicBlock *BB);
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/// Look through all the blocks in MergePotentials that have hash CurHash
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/// (guaranteed to match the last element). Build the vector SameTails of
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/// all those that have the (same) largest number of instructions in common
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/// of any pair of these blocks. SameTails entries contain an iterator into
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/// MergePotentials (from which the MachineBasicBlock can be found) and a
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/// MachineBasicBlock::iterator into that MBB indicating the instruction
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/// where the matching code sequence begins. Order of elements in SameTails
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/// is the reverse of the order in which those blocks appear in
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/// MergePotentials (where they are not necessarily consecutive).
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unsigned ComputeSameTails(unsigned CurHash, unsigned minCommonTailLength,
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MachineBasicBlock *SuccBB,
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MachineBasicBlock *PredBB);
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/// Remove all blocks with hash CurHash from MergePotentials, restoring
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/// branches at ends of blocks as appropriate.
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void RemoveBlocksWithHash(unsigned CurHash, MachineBasicBlock* SuccBB,
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MachineBasicBlock* PredBB);
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/// None of the blocks to be tail-merged consist only of the common tail.
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/// Create a block that does by splitting one.
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bool CreateCommonTailOnlyBlock(MachineBasicBlock *&PredBB,
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MachineBasicBlock *SuccBB,
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unsigned maxCommonTailLength,
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unsigned &commonTailIndex);
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/// Create merged DebugLocs of identical instructions across SameTails and
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/// assign it to the instruction in common tail; merge MMOs and undef flags.
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void mergeCommonTails(unsigned commonTailIndex);
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bool OptimizeBranches(MachineFunction &MF);
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/// Analyze and optimize control flow related to the specified block. This
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/// is never called on the entry block.
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bool OptimizeBlock(MachineBasicBlock *MBB);
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/// Remove the specified dead machine basic block from the function,
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/// updating the CFG.
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void RemoveDeadBlock(MachineBasicBlock *MBB);
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/// Hoist common instruction sequences at the start of basic blocks to their
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/// common predecessor.
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bool HoistCommonCode(MachineFunction &MF);
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/// If the successors of MBB has common instruction sequence at the start of
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/// the function, move the instructions before MBB terminator if it's legal.
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bool HoistCommonCodeInSuccs(MachineBasicBlock *MBB);
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};
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} // end namespace llvm
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#endif // LLVM_LIB_CODEGEN_BRANCHFOLDING_H
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