1 //===- AssumptionCache.cpp - Cache finding @llvm.assume calls -------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file contains a pass that keeps track of @llvm.assume intrinsics in
11 // the functions of a module.
12 //
13 //===----------------------------------------------------------------------===//
14
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/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
updateAffectedValues(CallInst * CI)57 void AssumptionCache::updateAffectedValues(CallInst *CI) {
58 // Note: This code must be kept in-sync with the code in
59 // computeKnownBitsFromAssume in ValueTracking.
60
61 SmallVector<Value *, 16> Affected;
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 for (auto &AV : Affected) {
114 auto &AVV = getOrInsertAffectedValues(AV);
115 if (std::find(AVV.begin(), AVV.end(), CI) == AVV.end())
116 AVV.push_back(CI);
117 }
118 }
119
deleted()120 void AssumptionCache::AffectedValueCallbackVH::deleted() {
121 auto AVI = AC->AffectedValues.find(getValPtr());
122 if (AVI != AC->AffectedValues.end())
123 AC->AffectedValues.erase(AVI);
124 // 'this' now dangles!
125 }
126
copyAffectedValuesInCache(Value * OV,Value * NV)127 void AssumptionCache::copyAffectedValuesInCache(Value *OV, Value *NV) {
128 auto &NAVV = getOrInsertAffectedValues(NV);
129 auto AVI = AffectedValues.find(OV);
130 if (AVI == AffectedValues.end())
131 return;
132
133 for (auto &A : AVI->second)
134 if (std::find(NAVV.begin(), NAVV.end(), A) == NAVV.end())
135 NAVV.push_back(A);
136 }
137
allUsesReplacedWith(Value * NV)138 void AssumptionCache::AffectedValueCallbackVH::allUsesReplacedWith(Value *NV) {
139 if (!isa<Instruction>(NV) && !isa<Argument>(NV))
140 return;
141
142 // Any assumptions that affected this value now affect the new value.
143
144 AC->copyAffectedValuesInCache(getValPtr(), NV);
145 // 'this' now might dangle! If the AffectedValues map was resized to add an
146 // entry for NV then this object might have been destroyed in favor of some
147 // copy in the grown map.
148 }
149
scanFunction()150 void AssumptionCache::scanFunction() {
151 assert(!Scanned && "Tried to scan the function twice!");
152 assert(AssumeHandles.empty() && "Already have assumes when scanning!");
153
154 // Go through all instructions in all blocks, add all calls to @llvm.assume
155 // to this cache.
156 for (BasicBlock &B : F)
157 for (Instruction &II : B)
158 if (match(&II, m_Intrinsic<Intrinsic::assume>()))
159 AssumeHandles.push_back(&II);
160
161 // Mark the scan as complete.
162 Scanned = true;
163
164 // Update affected values.
165 for (auto &A : AssumeHandles)
166 updateAffectedValues(cast<CallInst>(A));
167 }
168
registerAssumption(CallInst * CI)169 void AssumptionCache::registerAssumption(CallInst *CI) {
170 assert(match(CI, m_Intrinsic<Intrinsic::assume>()) &&
171 "Registered call does not call @llvm.assume");
172
173 // If we haven't scanned the function yet, just drop this assumption. It will
174 // be found when we scan later.
175 if (!Scanned)
176 return;
177
178 AssumeHandles.push_back(CI);
179
180 #ifndef NDEBUG
181 assert(CI->getParent() &&
182 "Cannot register @llvm.assume call not in a basic block");
183 assert(&F == CI->getParent()->getParent() &&
184 "Cannot register @llvm.assume call not in this function");
185
186 // We expect the number of assumptions to be small, so in an asserts build
187 // check that we don't accumulate duplicates and that all assumptions point
188 // to the same function.
189 SmallPtrSet<Value *, 16> AssumptionSet;
190 for (auto &VH : AssumeHandles) {
191 if (!VH)
192 continue;
193
194 assert(&F == cast<Instruction>(VH)->getParent()->getParent() &&
195 "Cached assumption not inside this function!");
196 assert(match(cast<CallInst>(VH), m_Intrinsic<Intrinsic::assume>()) &&
197 "Cached something other than a call to @llvm.assume!");
198 assert(AssumptionSet.insert(VH).second &&
199 "Cache contains multiple copies of a call!");
200 }
201 #endif
202
203 updateAffectedValues(CI);
204 }
205
206 AnalysisKey AssumptionAnalysis::Key;
207
run(Function & F,FunctionAnalysisManager & AM)208 PreservedAnalyses AssumptionPrinterPass::run(Function &F,
209 FunctionAnalysisManager &AM) {
210 AssumptionCache &AC = AM.getResult<AssumptionAnalysis>(F);
211
212 OS << "Cached assumptions for function: " << F.getName() << "\n";
213 for (auto &VH : AC.assumptions())
214 if (VH)
215 OS << " " << *cast<CallInst>(VH)->getArgOperand(0) << "\n";
216
217 return PreservedAnalyses::all();
218 }
219
deleted()220 void AssumptionCacheTracker::FunctionCallbackVH::deleted() {
221 auto I = ACT->AssumptionCaches.find_as(cast<Function>(getValPtr()));
222 if (I != ACT->AssumptionCaches.end())
223 ACT->AssumptionCaches.erase(I);
224 // 'this' now dangles!
225 }
226
getAssumptionCache(Function & F)227 AssumptionCache &AssumptionCacheTracker::getAssumptionCache(Function &F) {
228 // We probe the function map twice to try and avoid creating a value handle
229 // around the function in common cases. This makes insertion a bit slower,
230 // but if we have to insert we're going to scan the whole function so that
231 // shouldn't matter.
232 auto I = AssumptionCaches.find_as(&F);
233 if (I != AssumptionCaches.end())
234 return *I->second;
235
236 // Ok, build a new cache by scanning the function, insert it and the value
237 // handle into our map, and return the newly populated cache.
238 auto IP = AssumptionCaches.insert(std::make_pair(
239 FunctionCallbackVH(&F, this), llvm::make_unique<AssumptionCache>(F)));
240 assert(IP.second && "Scanning function already in the map?");
241 return *IP.first->second;
242 }
243
verifyAnalysis() const244 void AssumptionCacheTracker::verifyAnalysis() const {
245 // FIXME: In the long term the verifier should not be controllable with a
246 // flag. We should either fix all passes to correctly update the assumption
247 // cache and enable the verifier unconditionally or somehow arrange for the
248 // assumption list to be updated automatically by passes.
249 if (!VerifyAssumptionCache)
250 return;
251
252 SmallPtrSet<const CallInst *, 4> AssumptionSet;
253 for (const auto &I : AssumptionCaches) {
254 for (auto &VH : I.second->assumptions())
255 if (VH)
256 AssumptionSet.insert(cast<CallInst>(VH));
257
258 for (const BasicBlock &B : cast<Function>(*I.first))
259 for (const Instruction &II : B)
260 if (match(&II, m_Intrinsic<Intrinsic::assume>()) &&
261 !AssumptionSet.count(cast<CallInst>(&II)))
262 report_fatal_error("Assumption in scanned function not in cache");
263 }
264 }
265
AssumptionCacheTracker()266 AssumptionCacheTracker::AssumptionCacheTracker() : ImmutablePass(ID) {
267 initializeAssumptionCacheTrackerPass(*PassRegistry::getPassRegistry());
268 }
269
270 AssumptionCacheTracker::~AssumptionCacheTracker() = default;
271
272 char AssumptionCacheTracker::ID = 0;
273
274 INITIALIZE_PASS(AssumptionCacheTracker, "assumption-cache-tracker",
275 "Assumption Cache Tracker", false, true)
276