//===- Mem2Reg.cpp - The -mem2reg pass, a wrapper around the Utils lib ----===//

//

// 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 a simple pass wrapper around the PromoteMemToReg function call

// exposed by the Utils library.

//

//===----------------------------------------------------------------------===//

#include "llvm/Transforms/Utils/Mem2Reg.h"

#include "llvm/ADT/Statistic.h"

#include "llvm/Analysis/AssumptionCache.h"

#include "llvm/IR/BasicBlock.h"

#include "llvm/IR/Dominators.h"

#include "llvm/IR/Function.h"

#include "llvm/IR/Instructions.h"

#include "llvm/IR/PassManager.h"

#include "llvm/InitializePasses.h"

#include "llvm/Pass.h"

#include "llvm/Support/Casting.h"

#include "llvm/Transforms/Utils.h"

#include "llvm/Transforms/Utils/PromoteMemToReg.h"

#include <vector>

using namespace llvm;

#define DEBUG_TYPE "mem2reg"

STATISTIC(NumPromoted, "Number of alloca's promoted");

static bool promoteMemoryToRegister(Function &F, DominatorTree &DT,

                                    AssumptionCache &AC) {

  std::vector<AllocaInst *> Allocas;

  BasicBlock &BB = F.getEntryBlock(); // Get the entry node for the function

  bool Changed = false;

  while (true) {

    Allocas.clear();

    // Find allocas that are safe to promote, by looking at all instructions in

    // the entry node

    for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I)

      if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) // Is it an alloca?

        if (isAllocaPromotable(AI))

          Allocas.push_back(AI);

    if (Allocas.empty())

      break;

    PromoteMemToReg(Allocas, DT, &AC);

    NumPromoted += Allocas.size();

    Changed = true;

  }

  return Changed;

}

PreservedAnalyses PromotePass::run(Function &F, FunctionAnalysisManager &AM) {

  auto &DT = AM.getResult<DominatorTreeAnalysis>(F);

  auto &AC = AM.getResult<AssumptionAnalysis>(F);

  if (!promoteMemoryToRegister(F, DT, AC))

    return PreservedAnalyses::all();

  PreservedAnalyses PA;

  PA.preserveSet<CFGAnalyses>();

  return PA;

}

namespace {

struct PromoteLegacyPass : public FunctionPass {

  // Pass identification, replacement for typeid

  static char ID;

  bool ForcePass; /// If true, forces pass to execute, instead of skipping.

  PromoteLegacyPass() : FunctionPass(ID), ForcePass(false) {

    initializePromoteLegacyPassPass(*PassRegistry::getPassRegistry());

  }

  PromoteLegacyPass(bool IsForced) : FunctionPass(ID), ForcePass(IsForced) {

    initializePromoteLegacyPassPass(*PassRegistry::getPassRegistry());

  }

  // runOnFunction - To run this pass, first we calculate the alloca

  // instructions that are safe for promotion, then we promote each one.

  bool runOnFunction(Function &F) override {

    if (!ForcePass && skipFunction(F))

      return false;

    DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();

    AssumptionCache &AC =

        getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);

    return promoteMemoryToRegister(F, DT, AC);

  }

  void getAnalysisUsage(AnalysisUsage &AU) const override {

    AU.addRequired<AssumptionCacheTracker>();

    AU.addRequired<DominatorTreeWrapperPass>();

    AU.setPreservesCFG();

  }

};

} // end anonymous namespace

char PromoteLegacyPass::ID = 0;

INITIALIZE_PASS_BEGIN(PromoteLegacyPass, "mem2reg", "Promote Memory to "

                                                    "Register",

                      false, false)

INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)

INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)

INITIALIZE_PASS_END(PromoteLegacyPass, "mem2reg", "Promote Memory to Register",

                    false, false)

// createPromoteMemoryToRegister - Provide an entry point to create this pass.

FunctionPass *llvm::createPromoteMemoryToRegisterPass(bool IsForced) {

  return new PromoteLegacyPass(IsForced);

}