InstructionWorklist.h

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//=== InstructionWorklist.h - Worklist for InstCombine & others -*- 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
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_TRANSFORMS_UTILS_INSTRUCTIONWORKLIST_H
#define LLVM_TRANSFORMS_UTILS_INSTRUCTIONWORKLIST_H
 
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/IR/Instruction.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
 
namespace llvm {
 
/// InstructionWorklist - This is the worklist management logic for
/// InstCombine and other simplification passes.
class InstructionWorklist {
  SmallVector<Instruction *, 256> Worklist;
  DenseMap<Instruction *, unsigned> WorklistMap;
  /// These instructions will be added in reverse order after the current
  /// combine has finished. This means that these instructions will be visited
  /// in the order they have been added.
  SmallSetVector<Instruction *, 16> Deferred;
 
public:
  InstructionWorklist() = default;
 
  InstructionWorklist(InstructionWorklist &&) = default;
  InstructionWorklist &operator=(InstructionWorklist &&) = default;
 
  bool isEmpty() const { return Worklist.empty() && Deferred.empty(); }
 
  /// Add instruction to the worklist.
  /// Instructions will be visited in the order they are added.
  /// You likely want to use this method.
  void add(Instruction *I) {
    if (Deferred.insert(I))
      LLVM_DEBUG(dbgs() << "ADD DEFERRED: " << *I << '\n');
  }
 
  /// Add value to the worklist if it is an instruction.
  /// Instructions will be visited in the order they are added.
  void addValue(Value *V) {
    if (Instruction *I = dyn_cast<Instruction>(V))
      add(I);
  }
 
  /// Push the instruction onto the worklist stack.
  /// Instructions that have been added first will be visited last.
  void push(Instruction *I) {
    assert(I);
    assert(I->getParent() && "Instruction not inserted yet?");
 
    if (WorklistMap.insert(std::make_pair(I, Worklist.size())).second) {
      LLVM_DEBUG(dbgs() << "ADD: " << *I << '\n');
      Worklist.push_back(I);
    }
  }
 
  void pushValue(Value *V) {
    if (Instruction *I = dyn_cast<Instruction>(V))
      push(I);
  }
 
  Instruction *popDeferred() {
    if (Deferred.empty())
      return nullptr;
    return Deferred.pop_back_val();
  }
 
  void reserve(size_t Size) {
    Worklist.reserve(Size + 16);
    WorklistMap.reserve(Size);
  }
 
  /// Remove I from the worklist if it exists.
  void remove(Instruction *I) {
    DenseMap<Instruction *, unsigned>::iterator It = WorklistMap.find(I);
    if (It != WorklistMap.end()) {
      // Don't bother moving everything down, just null out the slot.
      Worklist[It->second] = nullptr;
      WorklistMap.erase(It);
    }
 
    Deferred.remove(I);
  }
 
  Instruction *removeOne() {
    if (Worklist.empty())
      return nullptr;
    Instruction *I = Worklist.pop_back_val();
    WorklistMap.erase(I);
    return I;
  }
 
  /// When an instruction is simplified, add all users of the instruction
  /// to the work lists because they might get more simplified now.
  void pushUsersToWorkList(Instruction &I) {
    for (User *U : I.users())
      push(cast<Instruction>(U));
  }
 
  /// Should be called *after* decrementing the use-count on V.
  void handleUseCountDecrement(Value *V) {
    if (auto *I = dyn_cast<Instruction>(V)) {
      add(I);
      // Many folds have one-use limitations. If there's only one use left,
      // revisit that use.
      if (I->hasOneUse())
        add(cast<Instruction>(*I->user_begin()));
    }
  }
 
  /// Check that the worklist is empty and nuke the backing store for the map.
  void zap() {
    assert(WorklistMap.empty() && "Worklist empty, but map not?");
    assert(Deferred.empty() && "Deferred instructions left over");
 
    // Do an explicit clear, this shrinks the map if needed.
    WorklistMap.clear();
  }
};
 
} // end namespace llvm.
 
#endif