3e39b27101
Adds a pass ExpandLargeDivRem to expand div/rem instructions with more than 128 bits into a loop computing that value. As discussed on https://reviews.llvm.org/D120327, this approach has the advantage that it is independent of the runtime library. This also helps the clang driver, which otherwise would need to understand enough about the runtime library to know whether to allow _BitInts with more than 128 bits. Targets are still free to disable this pass and instead provide a faster implementation in a runtime library. Fixes https://github.com/llvm/llvm-project/issues/44994 Differential Revision: https://reviews.llvm.org/D126644
113 lines
3.4 KiB
C++
113 lines
3.4 KiB
C++
//===--- ExpandLargeDivRem.cpp - Expand large div/rem ---------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass expands div/rem instructions with a bitwidth above a threshold
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// into a call to auto-generated functions.
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// This is useful for targets like x86_64 that cannot lower divisions
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// with more than 128 bits or targets like x86_32 that cannot lower divisions
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// with more than 64 bits.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/CodeGen/ExpandLargeDivRem.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/StringExtras.h"
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#include "llvm/Analysis/GlobalsModRef.h"
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/IR/IRBuilder.h"
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#include "llvm/IR/InstIterator.h"
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#include "llvm/IR/PassManager.h"
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#include "llvm/InitializePasses.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Transforms/Utils/IntegerDivision.h"
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using namespace llvm;
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static cl::opt<unsigned>
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ExpandDivRemBits("expand-div-rem-bits", cl::Hidden, cl::init(128),
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cl::desc("div and rem instructions on integers with "
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"more than <N> bits are expanded."));
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static bool runImpl(Function &F) {
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SmallVector<BinaryOperator *, 4> Replace;
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bool Modified = false;
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for (auto &I : instructions(F)) {
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switch (I.getOpcode()) {
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case Instruction::UDiv:
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case Instruction::SDiv:
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case Instruction::URem:
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case Instruction::SRem: {
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// TODO: This doesn't handle vectors.
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auto *IntTy = dyn_cast<IntegerType>(I.getType());
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if (!IntTy || IntTy->getIntegerBitWidth() <= ExpandDivRemBits)
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continue;
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Replace.push_back(&cast<BinaryOperator>(I));
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Modified = true;
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break;
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}
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default:
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break;
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}
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}
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if (Replace.empty())
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return false;
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while (!Replace.empty()) {
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BinaryOperator *I = Replace.pop_back_val();
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if (I->getOpcode() == Instruction::UDiv ||
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I->getOpcode() == Instruction::SDiv) {
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expandDivision(I);
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} else {
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expandRemainder(I);
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}
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}
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return Modified;
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}
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PreservedAnalyses ExpandLargeDivRemPass::run(Function &F,
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FunctionAnalysisManager &AM) {
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bool Changed = runImpl(F);
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if (Changed)
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return PreservedAnalyses::none();
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return PreservedAnalyses::all();
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}
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class ExpandLargeDivRemLegacyPass : public FunctionPass {
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public:
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static char ID;
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ExpandLargeDivRemLegacyPass() : FunctionPass(ID) {
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initializeExpandLargeDivRemLegacyPassPass(*PassRegistry::getPassRegistry());
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}
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bool runOnFunction(Function &F) override { return runImpl(F); }
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.addPreserved<AAResultsWrapperPass>();
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AU.addPreserved<GlobalsAAWrapperPass>();
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}
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};
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char ExpandLargeDivRemLegacyPass::ID = 0;
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INITIALIZE_PASS_BEGIN(ExpandLargeDivRemLegacyPass, "expand-large-div-rem",
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"Expand large div/rem", false, false)
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INITIALIZE_PASS_END(ExpandLargeDivRemLegacyPass, "expand-large-div-rem",
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"Expand large div/rem", false, false)
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FunctionPass *llvm::createExpandLargeDivRemPass() {
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return new ExpandLargeDivRemLegacyPass();
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}
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