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   remove_if(AssumeHandles, [CI](WeakTrackingVH &VH) { return CI == VH; });
 134 }
 135
 136 void AssumptionCache::AffectedValueCallbackVH::deleted() {
 137   auto AVI = AC->AffectedValues.find(getValPtr());
 138   if (AVI != AC->AffectedValues.end())
 139     AC->AffectedValues.erase(AVI);
 140   // 'this' now dangles!
 141 }
 142
 143 void AssumptionCache::transferAffectedValuesInCache(Value *OV, Value *NV) {
 144   auto &NAVV = getOrInsertAffectedValues(NV);
 145   auto AVI = AffectedValues.find(OV);
 146   if (AVI == AffectedValues.end())
 147     return;
 148
 149   for (auto &A : AVI->second)
 150     if (std::find(NAVV.begin(), NAVV.end(), A) == NAVV.end())
 151       NAVV.push_back(A);
 152   AffectedValues.erase(OV);
 153 }
 154
 155 void AssumptionCache::AffectedValueCallbackVH::allUsesReplacedWith(Value *NV) {
 156   if (!isa<Instruction>(NV) && !isa<Argument>(NV))
 157     return;
 158
 159   // Any assumptions that affected this value now affect the new value.
 160
 161   AC->transferAffectedValuesInCache(getValPtr(), NV);
 162   // 'this' now might dangle! If the AffectedValues map was resized to add an
 163   // entry for NV then this object might have been destroyed in favor of some
 164   // copy in the grown map.
 165 }
 166
 167 void AssumptionCache::scanFunction() {
 168   assert(!Scanned && "Tried to scan the function twice!");
 169   assert(AssumeHandles.empty() && "Already have assumes when scanning!");
 170
 171   // Go through all instructions in all blocks, add all calls to @llvm.assume
 172   // to this cache.
 173   for (BasicBlock &B : F)
 174     for (Instruction &II : B)
 175       if (match(&II, m_Intrinsic<Intrinsic::assume>()))
 176         AssumeHandles.push_back(&II);
 177
 178   // Mark the scan as complete.
 179   Scanned = true;
 180
 181   // Update affected values.
 182   for (auto &A : AssumeHandles)
 183     updateAffectedValues(cast<CallInst>(A));
 184 }
 185
 186 void AssumptionCache::registerAssumption(CallInst *CI) {
 187   assert(match(CI, m_Intrinsic<Intrinsic::assume>()) &&
 188          "Registered call does not call @llvm.assume");
 189
 190   // If we haven't scanned the function yet, just drop this assumption. It will
 191   // be found when we scan later.
 192   if (!Scanned)
 193     return;
 194
 195   AssumeHandles.push_back(CI);
 196
 197 #ifndef NDEBUG
 198   assert(CI->getParent() &&
 199          "Cannot register @llvm.assume call not in a basic block");
 200   assert(&F == CI->getParent()->getParent() &&
 201          "Cannot register @llvm.assume call not in this function");
 202
 203   // We expect the number of assumptions to be small, so in an asserts build
 204   // check that we don't accumulate duplicates and that all assumptions point
 205   // to the same function.
 206   SmallPtrSet<Value *, 16> AssumptionSet;
 207   for (auto &VH : AssumeHandles) {
 208     if (!VH)
 209       continue;
 210
 211     assert(&F == cast<Instruction>(VH)->getParent()->getParent() &&
 212            "Cached assumption not inside this function!");
 213     assert(match(cast<CallInst>(VH), m_Intrinsic<Intrinsic::assume>()) &&
 214            "Cached something other than a call to @llvm.assume!");
 215     assert(AssumptionSet.insert(VH).second &&
 216            "Cache contains multiple copies of a call!");
 217   }
 218 #endif
 219
 220   updateAffectedValues(CI);
 221 }
 222
 223 AnalysisKey AssumptionAnalysis::Key;
 224
 225 PreservedAnalyses AssumptionPrinterPass::run(Function &F,
 226                                              FunctionAnalysisManager &AM) {
 227   AssumptionCache &AC = AM.getResult<AssumptionAnalysis>(F);
 228
 229   OS << "Cached assumptions for function: " << F.getName() << "\n";
 230   for (auto &VH : AC.assumptions())
 231     if (VH)
 232       OS << "  " << *cast<CallInst>(VH)->getArgOperand(0) << "\n";
 233
 234   return PreservedAnalyses::all();
 235 }
 236
 237 void AssumptionCacheTracker::FunctionCallbackVH::deleted() {
 238   auto I = ACT->AssumptionCaches.find_as(cast<Function>(getValPtr()));
 239   if (I != ACT->AssumptionCaches.end())
 240     ACT->AssumptionCaches.erase(I);
 241   // 'this' now dangles!
 242 }
 243
 244 AssumptionCache &AssumptionCacheTracker::getAssumptionCache(Function &F) {
 245   // We probe the function map twice to try and avoid creating a value handle
 246   // around the function in common cases. This makes insertion a bit slower,
 247   // but if we have to insert we're going to scan the whole function so that
 248   // shouldn't matter.
 249   auto I = AssumptionCaches.find_as(&F);
 250   if (I != AssumptionCaches.end())
 251     return *I->second;
 252
 253   // Ok, build a new cache by scanning the function, insert it and the value
 254   // handle into our map, and return the newly populated cache.
 255   auto IP = AssumptionCaches.insert(std::make_pair(
 256       FunctionCallbackVH(&F, this), std::make_unique<AssumptionCache>(F)));
 257   assert(IP.second && "Scanning function already in the map?");
 258   return *IP.first->second;
 259 }
 260
 261 AssumptionCache *AssumptionCacheTracker::lookupAssumptionCache(Function &F) {
 262   auto I = AssumptionCaches.find_as(&F);
 263   if (I != AssumptionCaches.end())
 264     return I->second.get();
 265   return nullptr;
 266 }
 267
 268 void AssumptionCacheTracker::verifyAnalysis() const {
 269   // FIXME: In the long term the verifier should not be controllable with a
 270   // flag. We should either fix all passes to correctly update the assumption
 271   // cache and enable the verifier unconditionally or somehow arrange for the
 272   // assumption list to be updated automatically by passes.
 273   if (!VerifyAssumptionCache)
 274     return;
 275
 276   SmallPtrSet<const CallInst *, 4> AssumptionSet;
 277   for (const auto &I : AssumptionCaches) {
 278     for (auto &VH : I.second->assumptions())
 279       if (VH)
 280         AssumptionSet.insert(cast<CallInst>(VH));
 281
 282     for (const BasicBlock &B : cast<Function>(*I.first))
 283       for (const Instruction &II : B)
 284         if (match(&II, m_Intrinsic<Intrinsic::assume>()) &&
 285             !AssumptionSet.count(cast<CallInst>(&II)))
 286           report_fatal_error("Assumption in scanned function not in cache");
 287   }
 288 }
 289
 290 AssumptionCacheTracker::AssumptionCacheTracker() : ImmutablePass(ID) {
 291   initializeAssumptionCacheTrackerPass(*PassRegistry::getPassRegistry());
 292 }
 293
 294 AssumptionCacheTracker::~AssumptionCacheTracker() = default;
 295
 296 char AssumptionCacheTracker::ID = 0;
 297
 298 INITIALIZE_PASS(AssumptionCacheTracker, "assumption-cache-tracker",
 299                 "Assumption Cache Tracker", false, true)