1 //===- AssumptionCache.cpp - Cache finding @llvm.assume calls -------------===//
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
7 //===----------------------------------------------------------------------===//
9 // This file contains a pass that keeps track of @llvm.assume intrinsics in
10 // the functions of a module.
12 //===----------------------------------------------------------------------===//
14 #include "llvm/Analysis/AssumeBundleQueries.h"
15 #include "llvm/Analysis/AssumptionCache.h"
16 #include "llvm/ADT/STLExtras.h"
17 #include "llvm/ADT/SmallPtrSet.h"
18 #include "llvm/ADT/SmallVector.h"
19 #include "llvm/IR/BasicBlock.h"
20 #include "llvm/IR/Function.h"
21 #include "llvm/IR/InstrTypes.h"
22 #include "llvm/IR/Instruction.h"
23 #include "llvm/IR/Instructions.h"
24 #include "llvm/IR/Intrinsics.h"
25 #include "llvm/IR/PassManager.h"
26 #include "llvm/IR/PatternMatch.h"
27 #include "llvm/InitializePasses.h"
28 #include "llvm/Pass.h"
29 #include "llvm/Support/Casting.h"
30 #include "llvm/Support/CommandLine.h"
31 #include "llvm/Support/ErrorHandling.h"
32 #include "llvm/Support/raw_ostream.h"
38 using namespace llvm::PatternMatch;
41 VerifyAssumptionCache("verify-assumption-cache", cl::Hidden,
42 cl::desc("Enable verification of assumption cache"),
45 SmallVector<AssumptionCache::ResultElem, 1> &
46 AssumptionCache::getOrInsertAffectedValues(Value *V) {
47 // Try using find_as first to avoid creating extra value handles just for the
48 // purpose of doing the lookup.
49 auto AVI = AffectedValues.find_as(V);
50 if (AVI != AffectedValues.end())
53 auto AVIP = AffectedValues.insert(
54 {AffectedValueCallbackVH(V, this), SmallVector<ResultElem, 1>()});
55 return AVIP.first->second;
59 findAffectedValues(CallInst *CI,
60 SmallVectorImpl<AssumptionCache::ResultElem> &Affected) {
61 // Note: This code must be kept in-sync with the code in
62 // computeKnownBitsFromAssume in ValueTracking.
64 auto AddAffected = [&Affected](Value *V, unsigned Idx =
65 AssumptionCache::ExprResultIdx) {
66 if (isa<Argument>(V)) {
67 Affected.push_back({V, Idx});
68 } else if (auto *I = dyn_cast<Instruction>(V)) {
69 Affected.push_back({I, Idx});
71 // Peek through unary operators to find the source of the condition.
73 if (match(I, m_BitCast(m_Value(Op))) ||
74 match(I, m_PtrToInt(m_Value(Op))) || match(I, m_Not(m_Value(Op)))) {
75 if (isa<Instruction>(Op) || isa<Argument>(Op))
76 Affected.push_back({Op, Idx});
81 for (unsigned Idx = 0; Idx != CI->getNumOperandBundles(); Idx++) {
82 if (CI->getOperandBundleAt(Idx).Inputs.size() > ABA_WasOn &&
83 CI->getOperandBundleAt(Idx).getTagName() != IgnoreBundleTag)
84 AddAffected(CI->getOperandBundleAt(Idx).Inputs[ABA_WasOn], Idx);
87 Value *Cond = CI->getArgOperand(0), *A, *B;
90 CmpInst::Predicate Pred;
91 if (match(Cond, m_ICmp(Pred, m_Value(A), m_Value(B)))) {
95 if (Pred == ICmpInst::ICMP_EQ) {
96 // For equality comparisons, we handle the case of bit inversion.
97 auto AddAffectedFromEq = [&AddAffected](Value *V) {
99 if (match(V, m_Not(m_Value(A)))) {
106 // (A & B) or (A | B) or (A ^ B).
107 if (match(V, m_BitwiseLogic(m_Value(A), m_Value(B)))) {
110 // (A << C) or (A >>_s C) or (A >>_u C) where C is some constant.
111 } else if (match(V, m_Shift(m_Value(A), m_ConstantInt(C)))) {
116 AddAffectedFromEq(A);
117 AddAffectedFromEq(B);
122 void AssumptionCache::updateAffectedValues(CallInst *CI) {
123 SmallVector<AssumptionCache::ResultElem, 16> Affected;
124 findAffectedValues(CI, Affected);
126 for (auto &AV : Affected) {
127 auto &AVV = getOrInsertAffectedValues(AV.Assume);
128 if (std::find_if(AVV.begin(), AVV.end(), [&](ResultElem &Elem) {
129 return Elem.Assume == CI && Elem.Index == AV.Index;
131 AVV.push_back({CI, AV.Index});
135 void AssumptionCache::unregisterAssumption(CallInst *CI) {
136 SmallVector<AssumptionCache::ResultElem, 16> Affected;
137 findAffectedValues(CI, Affected);
139 for (auto &AV : Affected) {
140 auto AVI = AffectedValues.find_as(AV.Assume);
141 if (AVI == AffectedValues.end())
144 bool HasNonnull = false;
145 for (ResultElem &Elem : AVI->second) {
146 if (Elem.Assume == CI) {
148 Elem.Assume = nullptr;
150 HasNonnull |= !!Elem.Assume;
151 if (HasNonnull && Found)
154 assert(Found && "already unregistered or incorrect cache state");
156 AffectedValues.erase(AVI);
160 remove_if(AssumeHandles, [CI](ResultElem &RE) { return CI == RE; }),
161 AssumeHandles.end());
164 void AssumptionCache::AffectedValueCallbackVH::deleted() {
165 auto AVI = AC->AffectedValues.find(getValPtr());
166 if (AVI != AC->AffectedValues.end())
167 AC->AffectedValues.erase(AVI);
168 // 'this' now dangles!
171 void AssumptionCache::transferAffectedValuesInCache(Value *OV, Value *NV) {
172 auto &NAVV = getOrInsertAffectedValues(NV);
173 auto AVI = AffectedValues.find(OV);
174 if (AVI == AffectedValues.end())
177 for (auto &A : AVI->second)
178 if (std::find(NAVV.begin(), NAVV.end(), A) == NAVV.end())
180 AffectedValues.erase(OV);
183 void AssumptionCache::AffectedValueCallbackVH::allUsesReplacedWith(Value *NV) {
184 if (!isa<Instruction>(NV) && !isa<Argument>(NV))
187 // Any assumptions that affected this value now affect the new value.
189 AC->transferAffectedValuesInCache(getValPtr(), NV);
190 // 'this' now might dangle! If the AffectedValues map was resized to add an
191 // entry for NV then this object might have been destroyed in favor of some
192 // copy in the grown map.
195 void AssumptionCache::scanFunction() {
196 assert(!Scanned && "Tried to scan the function twice!");
197 assert(AssumeHandles.empty() && "Already have assumes when scanning!");
199 // Go through all instructions in all blocks, add all calls to @llvm.assume
201 for (BasicBlock &B : F)
202 for (Instruction &II : B)
203 if (match(&II, m_Intrinsic<Intrinsic::assume>()))
204 AssumeHandles.push_back({&II, ExprResultIdx});
206 // Mark the scan as complete.
209 // Update affected values.
210 for (auto &A : AssumeHandles)
211 updateAffectedValues(cast<CallInst>(A));
214 void AssumptionCache::registerAssumption(CallInst *CI) {
215 assert(match(CI, m_Intrinsic<Intrinsic::assume>()) &&
216 "Registered call does not call @llvm.assume");
218 // If we haven't scanned the function yet, just drop this assumption. It will
219 // be found when we scan later.
223 AssumeHandles.push_back({CI, ExprResultIdx});
226 assert(CI->getParent() &&
227 "Cannot register @llvm.assume call not in a basic block");
228 assert(&F == CI->getParent()->getParent() &&
229 "Cannot register @llvm.assume call not in this function");
231 // We expect the number of assumptions to be small, so in an asserts build
232 // check that we don't accumulate duplicates and that all assumptions point
233 // to the same function.
234 SmallPtrSet<Value *, 16> AssumptionSet;
235 for (auto &VH : AssumeHandles) {
239 assert(&F == cast<Instruction>(VH)->getParent()->getParent() &&
240 "Cached assumption not inside this function!");
241 assert(match(cast<CallInst>(VH), m_Intrinsic<Intrinsic::assume>()) &&
242 "Cached something other than a call to @llvm.assume!");
243 assert(AssumptionSet.insert(VH).second &&
244 "Cache contains multiple copies of a call!");
248 updateAffectedValues(CI);
251 AnalysisKey AssumptionAnalysis::Key;
253 PreservedAnalyses AssumptionPrinterPass::run(Function &F,
254 FunctionAnalysisManager &AM) {
255 AssumptionCache &AC = AM.getResult<AssumptionAnalysis>(F);
257 OS << "Cached assumptions for function: " << F.getName() << "\n";
258 for (auto &VH : AC.assumptions())
260 OS << " " << *cast<CallInst>(VH)->getArgOperand(0) << "\n";
262 return PreservedAnalyses::all();
265 void AssumptionCacheTracker::FunctionCallbackVH::deleted() {
266 auto I = ACT->AssumptionCaches.find_as(cast<Function>(getValPtr()));
267 if (I != ACT->AssumptionCaches.end())
268 ACT->AssumptionCaches.erase(I);
269 // 'this' now dangles!
272 AssumptionCache &AssumptionCacheTracker::getAssumptionCache(Function &F) {
273 // We probe the function map twice to try and avoid creating a value handle
274 // around the function in common cases. This makes insertion a bit slower,
275 // but if we have to insert we're going to scan the whole function so that
277 auto I = AssumptionCaches.find_as(&F);
278 if (I != AssumptionCaches.end())
281 // Ok, build a new cache by scanning the function, insert it and the value
282 // handle into our map, and return the newly populated cache.
283 auto IP = AssumptionCaches.insert(std::make_pair(
284 FunctionCallbackVH(&F, this), std::make_unique<AssumptionCache>(F)));
285 assert(IP.second && "Scanning function already in the map?");
286 return *IP.first->second;
289 AssumptionCache *AssumptionCacheTracker::lookupAssumptionCache(Function &F) {
290 auto I = AssumptionCaches.find_as(&F);
291 if (I != AssumptionCaches.end())
292 return I->second.get();
296 void AssumptionCacheTracker::verifyAnalysis() const {
297 // FIXME: In the long term the verifier should not be controllable with a
298 // flag. We should either fix all passes to correctly update the assumption
299 // cache and enable the verifier unconditionally or somehow arrange for the
300 // assumption list to be updated automatically by passes.
301 if (!VerifyAssumptionCache)
304 SmallPtrSet<const CallInst *, 4> AssumptionSet;
305 for (const auto &I : AssumptionCaches) {
306 for (auto &VH : I.second->assumptions())
308 AssumptionSet.insert(cast<CallInst>(VH));
310 for (const BasicBlock &B : cast<Function>(*I.first))
311 for (const Instruction &II : B)
312 if (match(&II, m_Intrinsic<Intrinsic::assume>()) &&
313 !AssumptionSet.count(cast<CallInst>(&II)))
314 report_fatal_error("Assumption in scanned function not in cache");
318 AssumptionCacheTracker::AssumptionCacheTracker() : ImmutablePass(ID) {
319 initializeAssumptionCacheTrackerPass(*PassRegistry::getPassRegistry());
322 AssumptionCacheTracker::~AssumptionCacheTracker() = default;
324 char AssumptionCacheTracker::ID = 0;
326 INITIALIZE_PASS(AssumptionCacheTracker, "assumption-cache-tracker",
327 "Assumption Cache Tracker", false, true)