• Home
  • Line#
  • Scopes#
  • Navigate#
  • Raw
  • Download
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