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//===- LowerAllowCheckPass.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/LowerAllowCheckPass.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Analysis/OptimizationRemarkEmitter.h"
#include "llvm/Analysis/ProfileSummaryInfo.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DiagnosticInfo.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/RandomNumberGenerator.h"
#include <memory>
#include <random>
using namespace llvm;
#define DEBUG_TYPE "lower-allow-check"
static cl::opt<int>
HotPercentileCutoff("lower-allow-check-percentile-cutoff-hot",
cl::desc("Hot percentile cuttoff."));
static cl::opt<float>
RandomRate("lower-allow-check-random-rate",
cl::desc("Probability value in the range [0.0, 1.0] of "
"unconditional pseudo-random checks."));
STATISTIC(NumChecksTotal, "Number of checks");
STATISTIC(NumChecksRemoved, "Number of removed checks");
struct RemarkInfo {
ore::NV Kind;
ore::NV F;
ore::NV BB;
explicit RemarkInfo(IntrinsicInst *II)
: Kind("Kind", II->getArgOperand(0)),
F("Function", II->getParent()->getParent()),
BB("Block", II->getParent()->getName()) {}
};
static void emitRemark(IntrinsicInst *II, OptimizationRemarkEmitter &ORE,
bool Removed) {
if (Removed) {
ORE.emit([&]() {
RemarkInfo Info(II);
return OptimizationRemark(DEBUG_TYPE, "Removed", II)
<< "Removed check: Kind=" << Info.Kind << " F=" << Info.F
<< " BB=" << Info.BB;
});
} else {
ORE.emit([&]() {
RemarkInfo Info(II);
return OptimizationRemarkMissed(DEBUG_TYPE, "Allowed", II)
<< "Allowed check: Kind=" << Info.Kind << " F=" << Info.F
<< " BB=" << Info.BB;
});
}
}
static bool removeUbsanTraps(Function &F, const BlockFrequencyInfo &BFI,
const ProfileSummaryInfo *PSI,
OptimizationRemarkEmitter &ORE) {
SmallVector<std::pair<IntrinsicInst *, bool>, 16> ReplaceWithValue;
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::allow_ubsan_check:
case Intrinsic::allow_runtime_check: {
++NumChecksTotal;
bool IsHot = false;
if (PSI) {
uint64_t Count = BFI.getBlockProfileCount(&BB).value_or(0);
IsHot = PSI->isHotCountNthPercentile(HotPercentileCutoff, Count);
}
bool ToRemove = ShouldRemove(IsHot);
ReplaceWithValue.push_back({
II,
ToRemove,
});
if (ToRemove)
++NumChecksRemoved;
emitRemark(II, ORE, ToRemove);
break;
}
default:
break;
}
}
}
for (auto [I, V] : ReplaceWithValue) {
I->replaceAllUsesWith(ConstantInt::getBool(I->getType(), !V));
I->eraseFromParent();
}
return !ReplaceWithValue.empty();
}
PreservedAnalyses LowerAllowCheckPass::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);
OptimizationRemarkEmitter &ORE =
AM.getResult<OptimizationRemarkEmitterAnalysis>(F);
return removeUbsanTraps(F, BFI, PSI, ORE) ? PreservedAnalyses::none()
: PreservedAnalyses::all();
}
bool LowerAllowCheckPass::IsRequested() {
return RandomRate.getNumOccurrences() ||
HotPercentileCutoff.getNumOccurrences();
}
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