MachineBranchProbabilityInfo.h

Go to the documentation of this file.

//=- MachineBranchProbabilityInfo.h - Branch Probability Analysis -*- C++ -*-=//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This pass is used to evaluate branch probabilties on machine basic blocks.
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_CODEGEN_MACHINEBRANCHPROBABILITYINFO_H
#define LLVM_CODEGEN_MACHINEBRANCHPROBABILITYINFO_H
 
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachinePassManager.h"
#include "llvm/Pass.h"
#include "llvm/Support/BranchProbability.h"
 
namespace llvm {
 
class MachineBranchProbabilityInfo {
  // Default weight value. Used when we don't have information about the edge.
  // TODO: DEFAULT_WEIGHT makes sense during static predication, when none of
  // the successors have a weight yet. But it doesn't make sense when providing
  // weight to an edge that may have siblings with non-zero weights. This can
  // be handled various ways, but it's probably fine for an edge with unknown
  // weight to just "inherit" the non-zero weight of an adjacent successor.
  static const uint32_t DEFAULT_WEIGHT = 16;
 
public:
  bool invalidate(MachineFunction &, const PreservedAnalyses &PA,
                  MachineFunctionAnalysisManager::Invalidator &);
 
  // Return edge probability.
  BranchProbability getEdgeProbability(const MachineBasicBlock *Src,
                                       const MachineBasicBlock *Dst) const;
 
  // Same as above, but using a const_succ_iterator from Src. This is faster
  // when the iterator is already available.
  BranchProbability
  getEdgeProbability(const MachineBasicBlock *Src,
                     MachineBasicBlock::const_succ_iterator Dst) const;
 
  // A 'Hot' edge is an edge which probability is >= 80%.
  bool isEdgeHot(const MachineBasicBlock *Src,
                 const MachineBasicBlock *Dst) const;
 
  // Print value between 0 (0% probability) and 1 (100% probability),
  // however the value is never equal to 0, and can be 1 only iff SRC block
  // has only one successor.
  raw_ostream &printEdgeProbability(raw_ostream &OS,
                                    const MachineBasicBlock *Src,
                                    const MachineBasicBlock *Dst) const;
};
 
class MachineBranchProbabilityAnalysis
    : public AnalysisInfoMixin<MachineBranchProbabilityAnalysis> {
  friend AnalysisInfoMixin<MachineBranchProbabilityAnalysis>;
 
  static AnalysisKey Key;
 
public:
  using Result = MachineBranchProbabilityInfo;
 
  Result run(MachineFunction &, MachineFunctionAnalysisManager &);
};
 
class MachineBranchProbabilityPrinterPass
    : public PassInfoMixin<MachineBranchProbabilityPrinterPass> {
  raw_ostream &OS;
 
public:
  MachineBranchProbabilityPrinterPass(raw_ostream &OS) : OS(OS) {}
  PreservedAnalyses run(MachineFunction &MF,
                        MachineFunctionAnalysisManager &MFAM);
};
 
class MachineBranchProbabilityInfoWrapperPass : public ImmutablePass {
  virtual void anchor();
 
  MachineBranchProbabilityInfo MBPI;
 
public:
  static char ID;
 
  MachineBranchProbabilityInfoWrapperPass();
 
  void getAnalysisUsage(AnalysisUsage &AU) const override {
    AU.setPreservesAll();
  }
 
  MachineBranchProbabilityInfo &getMBPI() { return MBPI; }
  const MachineBranchProbabilityInfo &getMBPI() const { return MBPI; }
};
}
 
 
#endif