1 //===- LowerAllowCheckPass.cpp ----------------------------------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8
9 #include "llvm/Transforms/Instrumentation/LowerAllowCheckPass.h"
10
11 #include "llvm/ADT/SmallVector.h"
12 #include "llvm/ADT/Statistic.h"
13 #include "llvm/ADT/StringRef.h"
14 #include "llvm/Analysis/OptimizationRemarkEmitter.h"
15 #include "llvm/Analysis/ProfileSummaryInfo.h"
16 #include "llvm/IR/Constant.h"
17 #include "llvm/IR/Constants.h"
18 #include "llvm/IR/DiagnosticInfo.h"
19 #include "llvm/IR/Instructions.h"
20 #include "llvm/IR/IntrinsicInst.h"
21 #include "llvm/IR/Intrinsics.h"
22 #include "llvm/IR/Metadata.h"
23 #include "llvm/IR/Module.h"
24 #include "llvm/Support/RandomNumberGenerator.h"
25 #include <memory>
26 #include <random>
27
28 using namespace llvm;
29
30 #define DEBUG_TYPE "lower-allow-check"
31
32 static cl::opt<int>
33 HotPercentileCutoff("lower-allow-check-percentile-cutoff-hot",
34 cl::desc("Hot percentile cuttoff."));
35
36 static cl::opt<float>
37 RandomRate("lower-allow-check-random-rate",
38 cl::desc("Probability value in the range [0.0, 1.0] of "
39 "unconditional pseudo-random checks."));
40
41 STATISTIC(NumChecksTotal, "Number of checks");
42 STATISTIC(NumChecksRemoved, "Number of removed checks");
43
44 struct RemarkInfo {
45 ore::NV Kind;
46 ore::NV F;
47 ore::NV BB;
RemarkInfoRemarkInfo48 explicit RemarkInfo(IntrinsicInst *II)
49 : Kind("Kind", II->getArgOperand(0)),
50 F("Function", II->getParent()->getParent()),
51 BB("Block", II->getParent()->getName()) {}
52 };
53
emitRemark(IntrinsicInst * II,OptimizationRemarkEmitter & ORE,bool Removed)54 static void emitRemark(IntrinsicInst *II, OptimizationRemarkEmitter &ORE,
55 bool Removed) {
56 if (Removed) {
57 ORE.emit([&]() {
58 RemarkInfo Info(II);
59 return OptimizationRemark(DEBUG_TYPE, "Removed", II)
60 << "Removed check: Kind=" << Info.Kind << " F=" << Info.F
61 << " BB=" << Info.BB;
62 });
63 } else {
64 ORE.emit([&]() {
65 RemarkInfo Info(II);
66 return OptimizationRemarkMissed(DEBUG_TYPE, "Allowed", II)
67 << "Allowed check: Kind=" << Info.Kind << " F=" << Info.F
68 << " BB=" << Info.BB;
69 });
70 }
71 }
72
removeUbsanTraps(Function & F,const BlockFrequencyInfo & BFI,const ProfileSummaryInfo * PSI,OptimizationRemarkEmitter & ORE)73 static bool removeUbsanTraps(Function &F, const BlockFrequencyInfo &BFI,
74 const ProfileSummaryInfo *PSI,
75 OptimizationRemarkEmitter &ORE) {
76 SmallVector<std::pair<IntrinsicInst *, bool>, 16> ReplaceWithValue;
77 std::unique_ptr<RandomNumberGenerator> Rng;
78
79 auto ShouldRemove = [&](bool IsHot) {
80 if (!RandomRate.getNumOccurrences())
81 return IsHot;
82 if (!Rng)
83 Rng = F.getParent()->createRNG(F.getName());
84 std::bernoulli_distribution D(RandomRate);
85 return !D(*Rng);
86 };
87
88 for (BasicBlock &BB : F) {
89 for (Instruction &I : BB) {
90 IntrinsicInst *II = dyn_cast<IntrinsicInst>(&I);
91 if (!II)
92 continue;
93 auto ID = II->getIntrinsicID();
94 switch (ID) {
95 case Intrinsic::allow_ubsan_check:
96 case Intrinsic::allow_runtime_check: {
97 ++NumChecksTotal;
98
99 bool IsHot = false;
100 if (PSI) {
101 uint64_t Count = BFI.getBlockProfileCount(&BB).value_or(0);
102 IsHot = PSI->isHotCountNthPercentile(HotPercentileCutoff, Count);
103 }
104
105 bool ToRemove = ShouldRemove(IsHot);
106 ReplaceWithValue.push_back({
107 II,
108 ToRemove,
109 });
110 if (ToRemove)
111 ++NumChecksRemoved;
112 emitRemark(II, ORE, ToRemove);
113 break;
114 }
115 default:
116 break;
117 }
118 }
119 }
120
121 for (auto [I, V] : ReplaceWithValue) {
122 I->replaceAllUsesWith(ConstantInt::getBool(I->getType(), !V));
123 I->eraseFromParent();
124 }
125
126 return !ReplaceWithValue.empty();
127 }
128
run(Function & F,FunctionAnalysisManager & AM)129 PreservedAnalyses LowerAllowCheckPass::run(Function &F,
130 FunctionAnalysisManager &AM) {
131 if (F.isDeclaration())
132 return PreservedAnalyses::all();
133 auto &MAMProxy = AM.getResult<ModuleAnalysisManagerFunctionProxy>(F);
134 ProfileSummaryInfo *PSI =
135 MAMProxy.getCachedResult<ProfileSummaryAnalysis>(*F.getParent());
136 BlockFrequencyInfo &BFI = AM.getResult<BlockFrequencyAnalysis>(F);
137 OptimizationRemarkEmitter &ORE =
138 AM.getResult<OptimizationRemarkEmitterAnalysis>(F);
139
140 return removeUbsanTraps(F, BFI, PSI, ORE) ? PreservedAnalyses::none()
141 : PreservedAnalyses::all();
142 }
143
IsRequested()144 bool LowerAllowCheckPass::IsRequested() {
145 return RandomRate.getNumOccurrences() ||
146 HotPercentileCutoff.getNumOccurrences();
147 }
148