MachineBlockFrequencyInfo.h

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//===- MachineBlockFrequencyInfo.h - MBB Frequency 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
//
//===----------------------------------------------------------------------===//
//
// Loops should be simplified before this analysis.
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_CODEGEN_MACHINEBLOCKFREQUENCYINFO_H
#define LLVM_CODEGEN_MACHINEBLOCKFREQUENCYINFO_H
 
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/Support/BlockFrequency.h"
#include <cstdint>
#include <memory>
#include <optional>
 
namespace llvm {
 
template <class BlockT> class BlockFrequencyInfoImpl;
class MachineBasicBlock;
class MachineBranchProbabilityInfo;
class MachineFunction;
class MachineLoopInfo;
class raw_ostream;
 
/// MachineBlockFrequencyInfo pass uses BlockFrequencyInfoImpl implementation
/// to estimate machine basic block frequencies.
class MachineBlockFrequencyInfo : public MachineFunctionPass {
  using ImplType = BlockFrequencyInfoImpl<MachineBasicBlock>;
  std::unique_ptr<ImplType> MBFI;
 
public:
  static char ID;
 
  MachineBlockFrequencyInfo();
  explicit MachineBlockFrequencyInfo(MachineFunction &F,
                                     MachineBranchProbabilityInfo &MBPI,
                                     MachineLoopInfo &MLI);
  ~MachineBlockFrequencyInfo() override;
 
  void getAnalysisUsage(AnalysisUsage &AU) const override;
 
  bool runOnMachineFunction(MachineFunction &F) override;
 
  /// calculate - compute block frequency info for the given function.
  void calculate(const MachineFunction &F,
                 const MachineBranchProbabilityInfo &MBPI,
                 const MachineLoopInfo &MLI);
 
  void releaseMemory() override;
 
  /// getblockFreq - Return block frequency. Return 0 if we don't have the
  /// information. Please note that initial frequency is equal to 1024. It means
  /// that we should not rely on the value itself, but only on the comparison to
  /// the other block frequencies. We do this to avoid using of floating points.
  /// For example, to get the frequency of a block relative to the entry block,
  /// divide the integral value returned by this function (the
  /// BlockFrequency::getFrequency() value) by getEntryFreq().
  BlockFrequency getBlockFreq(const MachineBasicBlock *MBB) const;
 
  /// Compute the frequency of the block, relative to the entry block.
  /// This API assumes getEntryFreq() is non-zero.
  float getBlockFreqRelativeToEntryBlock(const MachineBasicBlock *MBB) const {
    assert(getEntryFreq() != 0 && "getEntryFreq() should not return 0 here!");
    return getBlockFreq(MBB).getFrequency() * (1.0f / getEntryFreq());
  }
 
  std::optional<uint64_t>
  getBlockProfileCount(const MachineBasicBlock *MBB) const;
  std::optional<uint64_t> getProfileCountFromFreq(uint64_t Freq) const;
 
  bool isIrrLoopHeader(const MachineBasicBlock *MBB) const;
 
  /// incrementally calculate block frequencies when we split edges, to avoid
  /// full CFG traversal.
  void onEdgeSplit(const MachineBasicBlock &NewPredecessor,
                   const MachineBasicBlock &NewSuccessor,
                   const MachineBranchProbabilityInfo &MBPI);
 
  const MachineFunction *getFunction() const;
  const MachineBranchProbabilityInfo *getMBPI() const;
 
  /// Pop up a ghostview window with the current block frequency propagation
  /// rendered using dot.
  void view(const Twine &Name, bool isSimple = true) const;
 
  // Print the block frequency Freq to OS using the current functions entry
  // frequency to convert freq into a relative decimal form.
  raw_ostream &printBlockFreq(raw_ostream &OS, const BlockFrequency Freq) const;
 
  // Convenience method that attempts to look up the frequency associated with
  // BB and print it to OS.
  raw_ostream &printBlockFreq(raw_ostream &OS,
                              const MachineBasicBlock *MBB) const;
 
  /// Divide a block's BlockFrequency::getFrequency() value by this value to
  /// obtain the entry block - relative frequency of said block.
  uint64_t getEntryFreq() const;
};
 
} // end namespace llvm
 
#endif // LLVM_CODEGEN_MACHINEBLOCKFREQUENCYINFO_H