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//===- RemoveTrapsPass.cpp --------------------------------------*- C++ -*-===//
//
// 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/Instrumentation/RemoveTrapsPass.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/ProfileSummaryInfo.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/Support/RandomNumberGenerator.h"
#include <memory>
#include <random>
using namespace llvm;
#define DEBUG_TYPE "remove-traps"
static cl::opt<int> HotPercentileCutoff("remove-traps-percentile-cutoff-hot",
cl::desc("Hot percentile cuttoff."));
static cl::opt<float>
RandomRate("remove-traps-random-rate",
cl::desc("Probability value in the range [0.0, 1.0] of "
"unconditional pseudo-random checks removal."));
STATISTIC(NumChecksTotal, "Number of checks");
STATISTIC(NumChecksRemoved, "Number of removed checks");
static bool removeUbsanTraps(Function &F, const BlockFrequencyInfo &BFI,
const ProfileSummaryInfo *PSI) {
SmallVector<IntrinsicInst *, 16> Remove;
std::unique_ptr<RandomNumberGenerator> Rng;
auto ShouldRemove = [&](bool IsHot) {
if (!RandomRate.getNumOccurrences())
return IsHot;
if (!Rng)
Rng = F.getParent()->createRNG(F.getName());
std::bernoulli_distribution D(RandomRate);
return D(*Rng);
};
for (BasicBlock &BB : F) {
for (Instruction &I : BB) {
IntrinsicInst *II = dyn_cast<IntrinsicInst>(&I);
if (!II)
continue;
auto ID = II->getIntrinsicID();
switch (ID) {
case Intrinsic::ubsantrap: {
++NumChecksTotal;
bool IsHot = false;
if (PSI) {
uint64_t Count = 0;
for (const auto *PR : predecessors(&BB))
Count += BFI.getBlockProfileCount(PR).value_or(0);
IsHot = PSI->isHotCountNthPercentile(HotPercentileCutoff, Count);
}
if (ShouldRemove(IsHot)) {
Remove.push_back(II);
++NumChecksRemoved;
}
break;
}
default:
break;
}
}
}
for (IntrinsicInst *I : Remove)
I->eraseFromParent();
return !Remove.empty();
}
PreservedAnalyses RemoveTrapsPass::run(Function &F,
FunctionAnalysisManager &AM) {
if (F.isDeclaration())
return PreservedAnalyses::all();
auto &MAMProxy = AM.getResult<ModuleAnalysisManagerFunctionProxy>(F);
ProfileSummaryInfo *PSI =
MAMProxy.getCachedResult<ProfileSummaryAnalysis>(*F.getParent());
BlockFrequencyInfo &BFI = AM.getResult<BlockFrequencyAnalysis>(F);
return removeUbsanTraps(F, BFI, PSI) ? PreservedAnalyses::none()
: PreservedAnalyses::all();
}
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