1 //===- AssumptionCache.cpp - Cache finding @llvm.assume calls -------------===//
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 // This file contains a pass that keeps track of @llvm.assume intrinsics in
10 // the functions of a module.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "llvm/Analysis/AssumptionCache.h"
15 #include "llvm/ADT/STLExtras.h"
16 #include "llvm/ADT/SmallPtrSet.h"
17 #include "llvm/ADT/SmallVector.h"
18 #include "llvm/IR/BasicBlock.h"
19 #include "llvm/IR/Function.h"
20 #include "llvm/IR/InstrTypes.h"
21 #include "llvm/IR/Instruction.h"
22 #include "llvm/IR/Instructions.h"
23 #include "llvm/IR/Intrinsics.h"
24 #include "llvm/IR/PassManager.h"
25 #include "llvm/IR/PatternMatch.h"
26 #include "llvm/InitializePasses.h"
27 #include "llvm/Pass.h"
28 #include "llvm/Support/Casting.h"
29 #include "llvm/Support/CommandLine.h"
30 #include "llvm/Support/ErrorHandling.h"
31 #include "llvm/Support/raw_ostream.h"
32 #include <algorithm>
33 #include <cassert>
34 #include <utility>
35
36 using namespace llvm;
37 using namespace llvm::PatternMatch;
38
39 static cl::opt<bool>
40 VerifyAssumptionCache("verify-assumption-cache", cl::Hidden,
41 cl::desc("Enable verification of assumption cache"),
42 cl::init(false));
43
44 SmallVector<WeakTrackingVH, 1> &
getOrInsertAffectedValues(Value * V)45 AssumptionCache::getOrInsertAffectedValues(Value *V) {
46 // Try using find_as first to avoid creating extra value handles just for the
47 // purpose of doing the lookup.
48 auto AVI = AffectedValues.find_as(V);
49 if (AVI != AffectedValues.end())
50 return AVI->second;
51
52 auto AVIP = AffectedValues.insert(
53 {AffectedValueCallbackVH(V, this), SmallVector<WeakTrackingVH, 1>()});
54 return AVIP.first->second;
55 }
56
findAffectedValues(CallInst * CI,SmallVectorImpl<Value * > & Affected)57 static void findAffectedValues(CallInst *CI,
58 SmallVectorImpl<Value *> &Affected) {
59 // Note: This code must be kept in-sync with the code in
60 // computeKnownBitsFromAssume in ValueTracking.
61
62 auto AddAffected = [&Affected](Value *V) {
63 if (isa<Argument>(V)) {
64 Affected.push_back(V);
65 } else if (auto *I = dyn_cast<Instruction>(V)) {
66 Affected.push_back(I);
67
68 // Peek through unary operators to find the source of the condition.
69 Value *Op;
70 if (match(I, m_BitCast(m_Value(Op))) ||
71 match(I, m_PtrToInt(m_Value(Op))) ||
72 match(I, m_Not(m_Value(Op)))) {
73 if (isa<Instruction>(Op) || isa<Argument>(Op))
74 Affected.push_back(Op);
75 }
76 }
77 };
78
79 Value *Cond = CI->getArgOperand(0), *A, *B;
80 AddAffected(Cond);
81
82 CmpInst::Predicate Pred;
83 if (match(Cond, m_ICmp(Pred, m_Value(A), m_Value(B)))) {
84 AddAffected(A);
85 AddAffected(B);
86
87 if (Pred == ICmpInst::ICMP_EQ) {
88 // For equality comparisons, we handle the case of bit inversion.
89 auto AddAffectedFromEq = [&AddAffected](Value *V) {
90 Value *A;
91 if (match(V, m_Not(m_Value(A)))) {
92 AddAffected(A);
93 V = A;
94 }
95
96 Value *B;
97 ConstantInt *C;
98 // (A & B) or (A | B) or (A ^ B).
99 if (match(V, m_BitwiseLogic(m_Value(A), m_Value(B)))) {
100 AddAffected(A);
101 AddAffected(B);
102 // (A << C) or (A >>_s C) or (A >>_u C) where C is some constant.
103 } else if (match(V, m_Shift(m_Value(A), m_ConstantInt(C)))) {
104 AddAffected(A);
105 }
106 };
107
108 AddAffectedFromEq(A);
109 AddAffectedFromEq(B);
110 }
111 }
112 }
113
updateAffectedValues(CallInst * CI)114 void AssumptionCache::updateAffectedValues(CallInst *CI) {
115 SmallVector<Value *, 16> Affected;
116 findAffectedValues(CI, Affected);
117
118 for (auto &AV : Affected) {
119 auto &AVV = getOrInsertAffectedValues(AV);
120 if (std::find(AVV.begin(), AVV.end(), CI) == AVV.end())
121 AVV.push_back(CI);
122 }
123 }
124
unregisterAssumption(CallInst * CI)125 void AssumptionCache::unregisterAssumption(CallInst *CI) {
126 SmallVector<Value *, 16> Affected;
127 findAffectedValues(CI, Affected);
128
129 for (auto &AV : Affected) {
130 auto AVI = AffectedValues.find_as(AV);
131 if (AVI != AffectedValues.end())
132 AffectedValues.erase(AVI);
133 }
134
135 AssumeHandles.erase(
136 remove_if(AssumeHandles, [CI](WeakTrackingVH &VH) { return CI == VH; }),
137 AssumeHandles.end());
138 }
139
deleted()140 void AssumptionCache::AffectedValueCallbackVH::deleted() {
141 auto AVI = AC->AffectedValues.find(getValPtr());
142 if (AVI != AC->AffectedValues.end())
143 AC->AffectedValues.erase(AVI);
144 // 'this' now dangles!
145 }
146
transferAffectedValuesInCache(Value * OV,Value * NV)147 void AssumptionCache::transferAffectedValuesInCache(Value *OV, Value *NV) {
148 auto &NAVV = getOrInsertAffectedValues(NV);
149 auto AVI = AffectedValues.find(OV);
150 if (AVI == AffectedValues.end())
151 return;
152
153 for (auto &A : AVI->second)
154 if (std::find(NAVV.begin(), NAVV.end(), A) == NAVV.end())
155 NAVV.push_back(A);
156 AffectedValues.erase(OV);
157 }
158
allUsesReplacedWith(Value * NV)159 void AssumptionCache::AffectedValueCallbackVH::allUsesReplacedWith(Value *NV) {
160 if (!isa<Instruction>(NV) && !isa<Argument>(NV))
161 return;
162
163 // Any assumptions that affected this value now affect the new value.
164
165 AC->transferAffectedValuesInCache(getValPtr(), NV);
166 // 'this' now might dangle! If the AffectedValues map was resized to add an
167 // entry for NV then this object might have been destroyed in favor of some
168 // copy in the grown map.
169 }
170
scanFunction()171 void AssumptionCache::scanFunction() {
172 assert(!Scanned && "Tried to scan the function twice!");
173 assert(AssumeHandles.empty() && "Already have assumes when scanning!");
174
175 // Go through all instructions in all blocks, add all calls to @llvm.assume
176 // to this cache.
177 for (BasicBlock &B : F)
178 for (Instruction &II : B)
179 if (match(&II, m_Intrinsic<Intrinsic::assume>()))
180 AssumeHandles.push_back(&II);
181
182 // Mark the scan as complete.
183 Scanned = true;
184
185 // Update affected values.
186 for (auto &A : AssumeHandles)
187 updateAffectedValues(cast<CallInst>(A));
188 }
189
registerAssumption(CallInst * CI)190 void AssumptionCache::registerAssumption(CallInst *CI) {
191 assert(match(CI, m_Intrinsic<Intrinsic::assume>()) &&
192 "Registered call does not call @llvm.assume");
193
194 // If we haven't scanned the function yet, just drop this assumption. It will
195 // be found when we scan later.
196 if (!Scanned)
197 return;
198
199 AssumeHandles.push_back(CI);
200
201 #ifndef NDEBUG
202 assert(CI->getParent() &&
203 "Cannot register @llvm.assume call not in a basic block");
204 assert(&F == CI->getParent()->getParent() &&
205 "Cannot register @llvm.assume call not in this function");
206
207 // We expect the number of assumptions to be small, so in an asserts build
208 // check that we don't accumulate duplicates and that all assumptions point
209 // to the same function.
210 SmallPtrSet<Value *, 16> AssumptionSet;
211 for (auto &VH : AssumeHandles) {
212 if (!VH)
213 continue;
214
215 assert(&F == cast<Instruction>(VH)->getParent()->getParent() &&
216 "Cached assumption not inside this function!");
217 assert(match(cast<CallInst>(VH), m_Intrinsic<Intrinsic::assume>()) &&
218 "Cached something other than a call to @llvm.assume!");
219 assert(AssumptionSet.insert(VH).second &&
220 "Cache contains multiple copies of a call!");
221 }
222 #endif
223
224 updateAffectedValues(CI);
225 }
226
227 AnalysisKey AssumptionAnalysis::Key;
228
run(Function & F,FunctionAnalysisManager & AM)229 PreservedAnalyses AssumptionPrinterPass::run(Function &F,
230 FunctionAnalysisManager &AM) {
231 AssumptionCache &AC = AM.getResult<AssumptionAnalysis>(F);
232
233 OS << "Cached assumptions for function: " << F.getName() << "\n";
234 for (auto &VH : AC.assumptions())
235 if (VH)
236 OS << " " << *cast<CallInst>(VH)->getArgOperand(0) << "\n";
237
238 return PreservedAnalyses::all();
239 }
240
deleted()241 void AssumptionCacheTracker::FunctionCallbackVH::deleted() {
242 auto I = ACT->AssumptionCaches.find_as(cast<Function>(getValPtr()));
243 if (I != ACT->AssumptionCaches.end())
244 ACT->AssumptionCaches.erase(I);
245 // 'this' now dangles!
246 }
247
getAssumptionCache(Function & F)248 AssumptionCache &AssumptionCacheTracker::getAssumptionCache(Function &F) {
249 // We probe the function map twice to try and avoid creating a value handle
250 // around the function in common cases. This makes insertion a bit slower,
251 // but if we have to insert we're going to scan the whole function so that
252 // shouldn't matter.
253 auto I = AssumptionCaches.find_as(&F);
254 if (I != AssumptionCaches.end())
255 return *I->second;
256
257 // Ok, build a new cache by scanning the function, insert it and the value
258 // handle into our map, and return the newly populated cache.
259 auto IP = AssumptionCaches.insert(std::make_pair(
260 FunctionCallbackVH(&F, this), std::make_unique<AssumptionCache>(F)));
261 assert(IP.second && "Scanning function already in the map?");
262 return *IP.first->second;
263 }
264
lookupAssumptionCache(Function & F)265 AssumptionCache *AssumptionCacheTracker::lookupAssumptionCache(Function &F) {
266 auto I = AssumptionCaches.find_as(&F);
267 if (I != AssumptionCaches.end())
268 return I->second.get();
269 return nullptr;
270 }
271
verifyAnalysis() const272 void AssumptionCacheTracker::verifyAnalysis() const {
273 // FIXME: In the long term the verifier should not be controllable with a
274 // flag. We should either fix all passes to correctly update the assumption
275 // cache and enable the verifier unconditionally or somehow arrange for the
276 // assumption list to be updated automatically by passes.
277 if (!VerifyAssumptionCache)
278 return;
279
280 SmallPtrSet<const CallInst *, 4> AssumptionSet;
281 for (const auto &I : AssumptionCaches) {
282 for (auto &VH : I.second->assumptions())
283 if (VH)
284 AssumptionSet.insert(cast<CallInst>(VH));
285
286 for (const BasicBlock &B : cast<Function>(*I.first))
287 for (const Instruction &II : B)
288 if (match(&II, m_Intrinsic<Intrinsic::assume>()) &&
289 !AssumptionSet.count(cast<CallInst>(&II)))
290 report_fatal_error("Assumption in scanned function not in cache");
291 }
292 }
293
AssumptionCacheTracker()294 AssumptionCacheTracker::AssumptionCacheTracker() : ImmutablePass(ID) {
295 initializeAssumptionCacheTrackerPass(*PassRegistry::getPassRegistry());
296 }
297
298 AssumptionCacheTracker::~AssumptionCacheTracker() = default;
299
300 char AssumptionCacheTracker::ID = 0;
301
302 INITIALIZE_PASS(AssumptionCacheTracker, "assumption-cache-tracker",
303 "Assumption Cache Tracker", false, true)
304