//===- InstSimplifyPass.cpp -----------------------------------------------===//

//

// 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

//

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

#include "llvm/Transforms/Scalar/InstSimplifyPass.h"

#include "llvm/ADT/SmallPtrSet.h"

#include "llvm/ADT/Statistic.h"

#include "llvm/Analysis/AssumptionCache.h"

#include "llvm/Analysis/InstructionSimplify.h"

#include "llvm/Analysis/TargetLibraryInfo.h"

#include "llvm/IR/Dominators.h"

#include "llvm/IR/Function.h"

#include "llvm/InitializePasses.h"

#include "llvm/Pass.h"

#include "llvm/Transforms/Scalar.h"

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

using namespace llvm;

#define DEBUG_TYPE "instsimplify"

STATISTIC(NumSimplified, "Number of redundant instructions removed");

static bool runImpl(Function &F, const SimplifyQuery &SQ) {

  SmallPtrSet<const Instruction *, 8> S1, S2, *ToSimplify = &S1, *Next = &S2;

  bool Changed = false;

  do {

    for (BasicBlock &BB : F) {

      // Unreachable code can take on strange forms that we are not prepared to

      // handle. For example, an instruction may have itself as an operand.

      if (!SQ.DT->isReachableFromEntry(&BB))

        continue;

      SmallVector<WeakTrackingVH, 8> DeadInstsInBB;

      for (Instruction &I : BB) {

        // The first time through the loop, ToSimplify is empty and we try to

        // simplify all instructions. On later iterations, ToSimplify is not

        // empty and we only bother simplifying instructions that are in it.

        if (!ToSimplify->empty() && !ToSimplify->count(&I))

          continue;

        // Don't waste time simplifying dead/unused instructions.

        if (isInstructionTriviallyDead(&I)) {

          DeadInstsInBB.push_back(&I);

          Changed = true;

        } else if (!I.use_empty()) {

          if (Value *V = simplifyInstruction(&I, SQ)) {

            // Mark all uses for resimplification next time round the loop.

            for (User *U : I.users())

              Next->insert(cast<Instruction>(U));

            I.replaceAllUsesWith(V);

            ++NumSimplified;

            Changed = true;

            // A call can get simplified, but it may not be trivially dead.

            if (isInstructionTriviallyDead(&I))

              DeadInstsInBB.push_back(&I);

          }

        }

      }

      RecursivelyDeleteTriviallyDeadInstructions(DeadInstsInBB, SQ.TLI);

    }

    // Place the list of instructions to simplify on the next loop iteration

    // into ToSimplify.

    std::swap(ToSimplify, Next);

    Next->clear();

  } while (!ToSimplify->empty());

  return Changed;

}

namespace {

struct InstSimplifyLegacyPass : public FunctionPass {

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

  InstSimplifyLegacyPass() : FunctionPass(ID) {

    initializeInstSimplifyLegacyPassPass(*PassRegistry::getPassRegistry());

  }

  void getAnalysisUsage(AnalysisUsage &AU) const override {

    AU.setPreservesCFG();

    AU.addRequired<DominatorTreeWrapperPass>();

    AU.addRequired<AssumptionCacheTracker>();

    AU.addRequired<TargetLibraryInfoWrapperPass>();

  }

  /// Remove instructions that simplify.

  bool runOnFunction(Function &F) override {

    if (skipFunction(F))

      return false;

    const DominatorTree *DT =

        &getAnalysis<DominatorTreeWrapperPass>().getDomTree();

    const TargetLibraryInfo *TLI =

        &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);

    AssumptionCache *AC =

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

    const DataLayout &DL = F.getParent()->getDataLayout();

    const SimplifyQuery SQ(DL, TLI, DT, AC);

    return runImpl(F, SQ);

  }

};

} // namespace

char InstSimplifyLegacyPass::ID = 0;

INITIALIZE_PASS_BEGIN(InstSimplifyLegacyPass, "instsimplify",

                      "Remove redundant instructions", false, false)

INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)

INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)

INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)

INITIALIZE_PASS_END(InstSimplifyLegacyPass, "instsimplify",

                    "Remove redundant instructions", false, false)

// Public interface to the simplify instructions pass.

FunctionPass *llvm::createInstSimplifyLegacyPass() {

  return new InstSimplifyLegacyPass();

}

PreservedAnalyses InstSimplifyPass::run(Function &F,

                                        FunctionAnalysisManager &AM) {

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

  auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);

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

  const DataLayout &DL = F.getParent()->getDataLayout();

  const SimplifyQuery SQ(DL, &TLI, &DT, &AC);

  bool Changed = runImpl(F, SQ);

  if (!Changed)

    return PreservedAnalyses::all();

  PreservedAnalyses PA;

  PA.preserveSet<CFGAnalyses>();

  return PA;

}