ReachingDefAnalysis.h

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//==--- llvm/CodeGen/ReachingDefAnalysis.h - Reaching Def 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
//
//===----------------------------------------------------------------------===//
//
/// \file Reaching Defs Analysis pass.
///
/// This pass tracks for each instruction what is the "closest" reaching def of
/// a given register. It is used by BreakFalseDeps (for clearance calculation)
/// and ExecutionDomainFix (for arbitrating conflicting domains).
///
/// Note that this is different from the usual definition notion of liveness.
/// The CPU doesn't care whether or not we consider a register killed.
///
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CODEGEN_REACHINGDEFSANALYSIS_H
#define LLVM_CODEGEN_REACHINGDEFSANALYSIS_H

#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/CodeGen/LoopTraversal.h"
#include "llvm/CodeGen/MachineFunctionPass.h"

namespace llvm {

class MachineBasicBlock;
class MachineInstr;

/// This class provides the reaching def analysis.
class ReachingDefAnalysis : public MachineFunctionPass {
private:
  MachineFunction *MF;
  const TargetRegisterInfo *TRI;
  unsigned NumRegUnits;
  /// Instruction that defined each register, relative to the beginning of the
  /// current basic block.  When a LiveRegsDefInfo is used to represent a
  /// live-out register, this value is relative to the end of the basic block,
  /// so it will be a negative number.
  using LiveRegsDefInfo = std::vector<int>;
  LiveRegsDefInfo LiveRegs;

  /// Keeps clearance information for all registers. Note that this
  /// is different from the usual definition notion of liveness. The CPU
  /// doesn't care whether or not we consider a register killed.
  using OutRegsInfoMap = SmallVector<LiveRegsDefInfo, 4>;
  OutRegsInfoMap MBBOutRegsInfos;

  /// Current instruction number.
  /// The first instruction in each basic block is 0.
  int CurInstr;

  /// Maps instructions to their instruction Ids, relative to the begining of
  /// their basic blocks.
  DenseMap<MachineInstr *, int> InstIds;

  /// All reaching defs of a given RegUnit for a given MBB.
  using MBBRegUnitDefs = SmallVector<int, 1>;
  /// All reaching defs of all reg units for a given MBB
  using MBBDefsInfo = std::vector<MBBRegUnitDefs>;
  /// All reaching defs of all reg units for a all MBBs
  using MBBReachingDefsInfo = SmallVector<MBBDefsInfo, 4>;
  MBBReachingDefsInfo MBBReachingDefs;

  /// Default values are 'nothing happened a long time ago'.
  const int ReachingDefDefaultVal = -(1 << 20);

public:
  static char ID; // Pass identification, replacement for typeid

  ReachingDefAnalysis() : MachineFunctionPass(ID) {
    initializeReachingDefAnalysisPass(*PassRegistry::getPassRegistry());
  }
  void releaseMemory() override;

  void getAnalysisUsage(AnalysisUsage &AU) const override {
    AU.setPreservesAll();
    MachineFunctionPass::getAnalysisUsage(AU);
  }

  bool runOnMachineFunction(MachineFunction &MF) override;

  MachineFunctionProperties getRequiredProperties() const override {
    return MachineFunctionProperties().set(
        MachineFunctionProperties::Property::NoVRegs);
  }

  /// Provides the instruction id of the closest reaching def instruction of
  /// PhysReg that reaches MI, relative to the begining of MI's basic block.
  int getReachingDef(MachineInstr *MI, int PhysReg);

  /// Provides the clearance - the number of instructions since the closest
  /// reaching def instuction of PhysReg that reaches MI.
  int getClearance(MachineInstr *MI, MCPhysReg PhysReg);

private:
  /// Set up LiveRegs by merging predecessor live-out values.
  void enterBasicBlock(const LoopTraversal::TraversedMBBInfo &TraversedMBB);

  /// Update live-out values.
  void leaveBasicBlock(const LoopTraversal::TraversedMBBInfo &TraversedMBB);

  /// Process he given basic block.
  void processBasicBlock(const LoopTraversal::TraversedMBBInfo &TraversedMBB);

  /// Update def-ages for registers defined by MI.
  /// Also break dependencies on partial defs and undef uses.
  void processDefs(MachineInstr *);
};

} // namespace llvm

#endif // LLVM_CODEGEN_REACHINGDEFSANALYSIS_H