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//===--- 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/CodeGen/TargetLowering.h"
#include "llvm/CodeGen/TargetPassConfig.h"
#include "llvm/CodeGen/TargetSubtargetInfo.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/Target/TargetMachine.h"
#include "llvm/Transforms/Utils/IntegerDivision.h"
using namespace llvm;
static cl::opt<unsigned>
ExpandDivRemBits("expand-div-rem-bits", cl::Hidden,
cl::init(llvm::IntegerType::MAX_INT_BITS),
cl::desc("div and rem instructions on integers with "
"more than <N> bits are expanded."));
static bool isConstantPowerOfTwo(llvm::Value *V, bool SignedOp) {
auto *C = dyn_cast<ConstantInt>(V);
if (!C)
return false;
APInt Val = C->getValue();
if (SignedOp && Val.isNegative())
Val = -Val;
return Val.isPowerOf2();
}
static bool isSigned(unsigned int Opcode) {
return Opcode == Instruction::SDiv || Opcode == Instruction::SRem;
}
static void scalarize(BinaryOperator *BO,
SmallVectorImpl<BinaryOperator *> &Replace) {
VectorType *VTy = cast<FixedVectorType>(BO->getType());
IRBuilder<> Builder(BO);
unsigned NumElements = VTy->getElementCount().getFixedValue();
Value *Result = PoisonValue::get(VTy);
for (unsigned Idx = 0; Idx < NumElements; ++Idx) {
Value *LHS = Builder.CreateExtractElement(BO->getOperand(0), Idx);
Value *RHS = Builder.CreateExtractElement(BO->getOperand(1), Idx);
Value *Op = Builder.CreateBinOp(BO->getOpcode(), LHS, RHS);
Result = Builder.CreateInsertElement(Result, Op, Idx);
if (auto *NewBO = dyn_cast<BinaryOperator>(Op)) {
NewBO->copyIRFlags(Op, true);
Replace.push_back(NewBO);
}
}
BO->replaceAllUsesWith(Result);
BO->dropAllReferences();
BO->eraseFromParent();
}
static bool runImpl(Function &F, const TargetLowering &TLI) {
SmallVector<BinaryOperator *, 4> Replace;
SmallVector<BinaryOperator *, 4> ReplaceVector;
bool Modified = false;
unsigned MaxLegalDivRemBitWidth = TLI.getMaxDivRemBitWidthSupported();
if (ExpandDivRemBits != llvm::IntegerType::MAX_INT_BITS)
MaxLegalDivRemBitWidth = ExpandDivRemBits;
if (MaxLegalDivRemBitWidth >= llvm::IntegerType::MAX_INT_BITS)
return false;
for (auto &I : instructions(F)) {
switch (I.getOpcode()) {
case Instruction::UDiv:
case Instruction::SDiv:
case Instruction::URem:
case Instruction::SRem: {
// TODO: This pass doesn't handle scalable vectors.
if (I.getOperand(0)->getType()->isScalableTy())
continue;
auto *IntTy = dyn_cast<IntegerType>(I.getType()->getScalarType());
if (!IntTy || IntTy->getIntegerBitWidth() <= MaxLegalDivRemBitWidth)
continue;
// The backend has peephole optimizations for powers of two.
// TODO: We don't consider vectors here.
if (isConstantPowerOfTwo(I.getOperand(1), isSigned(I.getOpcode())))
continue;
if (I.getOperand(0)->getType()->isVectorTy())
ReplaceVector.push_back(&cast<BinaryOperator>(I));
else
Replace.push_back(&cast<BinaryOperator>(I));
Modified = true;
break;
}
default:
break;
}
}
while (!ReplaceVector.empty()) {
BinaryOperator *BO = ReplaceVector.pop_back_val();
scalarize(BO, Replace);
}
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;
}
namespace {
class ExpandLargeDivRemLegacyPass : public FunctionPass {
public:
static char ID;
ExpandLargeDivRemLegacyPass() : FunctionPass(ID) {
initializeExpandLargeDivRemLegacyPassPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F) override {
auto *TM = &getAnalysis<TargetPassConfig>().getTM<TargetMachine>();
auto *TLI = TM->getSubtargetImpl(F)->getTargetLowering();
return runImpl(F, *TLI);
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<TargetPassConfig>();
AU.addPreserved<AAResultsWrapperPass>();
AU.addPreserved<GlobalsAAWrapperPass>();
}
};
} // namespace
PreservedAnalyses ExpandLargeDivRemPass::run(Function &F,
FunctionAnalysisManager &FAM) {
const TargetSubtargetInfo *STI = TM->getSubtargetImpl(F);
return runImpl(F, *STI->getTargetLowering()) ? PreservedAnalyses::none()
: PreservedAnalyses::all();
}
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();
}
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