a6a6fca791
UBSAN checks can be too expensive to be used in release binaries. However not all code affect performace in the same way. Removing small number of checks in hot code we can performance loss, preserving most of the checks.
105 lines
3.3 KiB
C++
105 lines
3.3 KiB
C++
//===- RemoveTrapsPass.cpp --------------------------------------*- C++ -*-===//
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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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#include "llvm/Transforms/Instrumentation/RemoveTrapsPass.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/ProfileSummaryInfo.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/IR/Intrinsics.h"
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#include "llvm/Support/RandomNumberGenerator.h"
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#include <memory>
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#include <random>
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using namespace llvm;
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#define DEBUG_TYPE "remove-traps"
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static cl::opt<int> HotPercentileCutoff(
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"remove-traps-percentile-cutoff-hot", cl::init(0),
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cl::desc("Alternative hot percentile cuttoff. By default "
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"`-profile-summary-cutoff-hot` is used."));
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static cl::opt<float>
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RandomRate("remove-traps-random-rate", cl::init(0.0),
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cl::desc("Probability value in the range [0.0, 1.0] of "
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"unconditional pseudo-random checks removal."));
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STATISTIC(NumChecksTotal, "Number of checks");
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STATISTIC(NumChecksRemoved, "Number of removed checks");
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static bool removeUbsanTraps(Function &F, const BlockFrequencyInfo &BFI,
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const ProfileSummaryInfo *PSI) {
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SmallVector<IntrinsicInst *, 16> Remove;
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std::unique_ptr<RandomNumberGenerator> Rng;
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auto ShouldRemove = [&](bool IsHot) {
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if (!RandomRate.getNumOccurrences())
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return IsHot;
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if (!Rng)
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Rng = F.getParent()->createRNG(F.getName());
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std::bernoulli_distribution D(RandomRate);
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return D(*Rng);
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};
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for (BasicBlock &BB : F) {
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for (Instruction &I : BB) {
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IntrinsicInst *II = dyn_cast<IntrinsicInst>(&I);
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if (!II)
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continue;
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auto ID = II->getIntrinsicID();
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switch (ID) {
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case Intrinsic::ubsantrap: {
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++NumChecksTotal;
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bool IsHot = false;
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if (PSI) {
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uint64_t Count = 0;
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for (const auto *PR : predecessors(&BB))
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Count += BFI.getBlockProfileCount(PR).value_or(0);
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IsHot =
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HotPercentileCutoff.getNumOccurrences()
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? (HotPercentileCutoff > 0 &&
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PSI->isHotCountNthPercentile(HotPercentileCutoff, Count))
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: PSI->isHotCount(Count);
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}
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if (ShouldRemove(IsHot)) {
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Remove.push_back(II);
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++NumChecksRemoved;
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}
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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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}
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for (IntrinsicInst *I : Remove)
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I->eraseFromParent();
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return !Remove.empty();
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}
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PreservedAnalyses RemoveTrapsPass::run(Function &F,
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FunctionAnalysisManager &AM) {
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if (F.isDeclaration())
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return PreservedAnalyses::all();
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auto &MAMProxy = AM.getResult<ModuleAnalysisManagerFunctionProxy>(F);
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ProfileSummaryInfo *PSI =
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MAMProxy.getCachedResult<ProfileSummaryAnalysis>(*F.getParent());
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BlockFrequencyInfo &BFI = AM.getResult<BlockFrequencyAnalysis>(F);
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return removeUbsanTraps(F, BFI, PSI) ? PreservedAnalyses::none()
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: PreservedAnalyses::all();
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}
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