llvm-project/llvm/lib/CodeGen/ExpandLargeDivRem.cpp

//===--- ExpandLargeDivRem.cpp - Expand large div/rem ---------------------===//
//
// 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 expands div/rem instructions with a bitwidth above a threshold
// into a call to auto-generated functions.
// This is useful for targets like x86_64 that cannot lower divisions
// with more than 128 bits or targets like x86_32 that cannot lower divisions
// with more than 64 bits.
//
//===----------------------------------------------------------------------===//

#include "llvm/CodeGen/ExpandLargeDivRem.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/PassManager.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Transforms/Utils/IntegerDivision.h"

using namespace llvm;

static cl::opt<unsigned>
    ExpandDivRemBits("expand-div-rem-bits", cl::Hidden, cl::init(128),
                     cl::desc("div and rem instructions on integers with "
                              "more than <N> bits are expanded."));

static bool runImpl(Function &F) {
  SmallVector<BinaryOperator *, 4> Replace;
  bool Modified = false;

  for (auto &I : instructions(F)) {
    switch (I.getOpcode()) {
    case Instruction::UDiv:
    case Instruction::SDiv:
    case Instruction::URem:
    case Instruction::SRem: {
      // TODO: This doesn't handle vectors.
      auto *IntTy = dyn_cast<IntegerType>(I.getType());
      if (!IntTy || IntTy->getIntegerBitWidth() <= ExpandDivRemBits)
        continue;

      Replace.push_back(&cast<BinaryOperator>(I));
      Modified = true;
      break;
    }
    default:
      break;
    }
  }

  if (Replace.empty())
    return false;

  while (!Replace.empty()) {
    BinaryOperator *I = Replace.pop_back_val();

    if (I->getOpcode() == Instruction::UDiv ||
        I->getOpcode() == Instruction::SDiv) {
      expandDivision(I);
    } else {
      expandRemainder(I);
    }
  }

  return Modified;
}

PreservedAnalyses ExpandLargeDivRemPass::run(Function &F,
                                             FunctionAnalysisManager &AM) {
  bool Changed = runImpl(F);

  if (Changed)
    return PreservedAnalyses::none();

  return PreservedAnalyses::all();
}

class ExpandLargeDivRemLegacyPass : public FunctionPass {
public:
  static char ID;

  ExpandLargeDivRemLegacyPass() : FunctionPass(ID) {
    initializeExpandLargeDivRemLegacyPassPass(*PassRegistry::getPassRegistry());
  }

  bool runOnFunction(Function &F) override { return runImpl(F); }

  void getAnalysisUsage(AnalysisUsage &AU) const override {
    AU.addPreserved<AAResultsWrapperPass>();
    AU.addPreserved<GlobalsAAWrapperPass>();
  }
};

char ExpandLargeDivRemLegacyPass::ID = 0;
INITIALIZE_PASS_BEGIN(ExpandLargeDivRemLegacyPass, "expand-large-div-rem",
                      "Expand large div/rem", false, false)
INITIALIZE_PASS_END(ExpandLargeDivRemLegacyPass, "expand-large-div-rem",
                    "Expand large div/rem", false, false)

FunctionPass *llvm::createExpandLargeDivRemPass() {
  return new ExpandLargeDivRemLegacyPass();
}