lib/Analysis/AssumptionCache.cpp

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