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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/StringExtras.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Analysis/OptimizationRemarkEmitter.h"
#include "llvm/Analysis/ProfileSummaryInfo.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DiagnosticInfo.h"
#include "llvm/IR/InstIterator.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/Debug.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 cutoff."));
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 lowerAllowChecks(Function &F, const BlockFrequencyInfo &BFI,
const ProfileSummaryInfo *PSI,
OptimizationRemarkEmitter &ORE,
const LowerAllowCheckPass::Options &Opts) {
SmallVector<std::pair<IntrinsicInst *, bool>, 16> ReplaceWithValue;
std::unique_ptr<RandomNumberGenerator> Rng;
auto GetRng = [&]() -> RandomNumberGenerator & {
if (!Rng)
Rng = F.getParent()->createRNG(F.getName());
return *Rng;
};
auto GetCutoff = [&](const IntrinsicInst *II) -> unsigned {
if (HotPercentileCutoff.getNumOccurrences())
return HotPercentileCutoff;
else if (II->getIntrinsicID() == Intrinsic::allow_ubsan_check) {
auto *Kind = cast<ConstantInt>(II->getArgOperand(0));
if (Kind->getZExtValue() < Opts.cutoffs.size())
return Opts.cutoffs[Kind->getZExtValue()];
} else if (II->getIntrinsicID() == Intrinsic::allow_runtime_check) {
return Opts.runtime_check;
}
return 0;
};
auto ShouldRemoveHot = [&](const BasicBlock &BB, unsigned int cutoff) {
return (cutoff == 1000000) ||
(PSI && PSI->isHotCountNthPercentile(
cutoff, BFI.getBlockProfileCount(&BB).value_or(0)));
};
auto ShouldRemoveRandom = [&]() {
return RandomRate.getNumOccurrences() &&
!std::bernoulli_distribution(RandomRate)(GetRng());
};
auto ShouldRemove = [&](const IntrinsicInst *II) {
unsigned int cutoff = GetCutoff(II);
return ShouldRemoveRandom() || ShouldRemoveHot(*(II->getParent()), cutoff);
};
for (Instruction &I : instructions(F)) {
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 ToRemove = ShouldRemove(II);
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 lowerAllowChecks(F, BFI, PSI, ORE, Opts)
// We do not change the CFG, we only replace the intrinsics with
// true or false.
? PreservedAnalyses::none().preserveSet<CFGAnalyses>()
: PreservedAnalyses::all();
}
bool LowerAllowCheckPass::IsRequested() {
return RandomRate.getNumOccurrences() ||
HotPercentileCutoff.getNumOccurrences();
}
void LowerAllowCheckPass::printPipeline(
raw_ostream &OS, function_ref<StringRef(StringRef)> MapClassName2PassName) {
static_cast<PassInfoMixin<LowerAllowCheckPass> *>(this)->printPipeline(
OS, MapClassName2PassName);
OS << "<";
// Format is <cutoffs[0,1,2]=70000;cutoffs[5,6,8]=90000>
// but it's equally valid to specify
// cutoffs[0]=70000;cutoffs[1]=70000;cutoffs[2]=70000;cutoffs[5]=90000;...
// and that's what we do here. It is verbose but valid and easy to verify
// correctness.
// TODO: print shorter output by combining adjacent runs, etc.
int i = 0;
ListSeparator LS(";");
for (unsigned int cutoff : Opts.cutoffs) {
if (cutoff > 0)
OS << LS << "cutoffs[" << i << "]=" << cutoff;
i++;
}
if (Opts.runtime_check)
OS << LS << "runtime_check=" << Opts.runtime_check;
OS << '>';
}
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