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//===- ConstantProp.cpp - Code to perform Simple Constant Propagation -----===//
//                     The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// This file implements constant propagation and merging:
// Specifically, this:
//   * Converts instructions like "add int 1, 2" into 3
// Notice that:
//   * This pass has a habit of making definitions be dead.  It is a good idea
//     to run a DIE pass sometime after running this pass.

#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/Instruction.h"
#include "llvm/Pass.h"
#include "llvm/Transforms/Scalar.h"
#include <set>
using namespace llvm;

#define DEBUG_TYPE "constprop"

STATISTIC(NumInstKilled, "Number of instructions killed");

namespace {
  struct ConstantPropagation : public FunctionPass {
    static char ID; // Pass identification, replacement for typeid
    ConstantPropagation() : FunctionPass(ID) {

    bool runOnFunction(Function &F) override;

    void getAnalysisUsage(AnalysisUsage &AU) const override {

char ConstantPropagation::ID = 0;
INITIALIZE_PASS_BEGIN(ConstantPropagation, "constprop",
                "Simple constant propagation", false, false)
INITIALIZE_PASS_END(ConstantPropagation, "constprop",
                "Simple constant propagation", false, false)

FunctionPass *llvm::createConstantPropagationPass() {
  return new ConstantPropagation();

bool ConstantPropagation::runOnFunction(Function &F) {
  if (skipFunction(F))
    return false;

  // Initialize the worklist to all of the instructions ready to process...
  std::set<Instruction*> WorkList;
  for (Instruction &I: instructions(&F))

  bool Changed = false;
  const DataLayout &DL = F.getParent()->getDataLayout();
  TargetLibraryInfo *TLI =

  while (!WorkList.empty()) {
    Instruction *I = *WorkList.begin();
    WorkList.erase(WorkList.begin());    // Get an element from the worklist...

    if (!I->use_empty())                 // Don't muck with dead instructions...
      if (Constant *C = ConstantFoldInstruction(I, DL, TLI)) {
        // Add all of the users of this instruction to the worklist, they might
        // be constant propagatable now...
        for (User *U : I->users())

        // Replace all of the uses of a variable with uses of the constant.

        // Remove the dead instruction.
        if (isInstructionTriviallyDead(I, TLI)) {

        // We made a change to the function...
        Changed = true;
  return Changed;