llvm/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/Analysis/AssumeBundleQueries.h"
  19 #include "llvm/Analysis/TargetTransformInfo.h"
  20 #include "llvm/Analysis/ValueTracking.h"
  21 #include "llvm/IR/BasicBlock.h"
  22 #include "llvm/IR/Function.h"
  23 #include "llvm/IR/InstrTypes.h"
  24 #include "llvm/IR/Instruction.h"
  25 #include "llvm/IR/Instructions.h"
  26 #include "llvm/IR/PassManager.h"
  27 #include "llvm/IR/PatternMatch.h"
  28 #include "llvm/InitializePasses.h"
  29 #include "llvm/Pass.h"
  30 #include "llvm/Support/Casting.h"
  31 #include "llvm/Support/CommandLine.h"
  32 #include "llvm/Support/ErrorHandling.h"
  33 #include "llvm/Support/raw_ostream.h"
  34 #include <cassert>
  35 #include <utility>
  36
  37 using namespace llvm;
  38 using namespace llvm::PatternMatch;
  39
  40 static cl::opt<bool>
  41     VerifyAssumptionCache("verify-assumption-cache", cl::Hidden,
  42                           cl::desc("Enable verification of assumption cache"),
  43                           cl::init(false));
  44
  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())
  51     return AVI->second;
  52
  53   return AffectedValues[AffectedValueCallbackVH(V, this)];
  54 }
  55
  56 static void
  57 findAffectedValues(CallBase *CI, TargetTransformInfo *TTI,
  58                    SmallVectorImpl<AssumptionCache::ResultElem> &Affected) {
  59   // Note: This code must be kept in-sync with the code in
  60   // computeKnownBitsFromAssume in ValueTracking.
  61
  62   auto InsertAffected = [&Affected](Value *V) {
  63     Affected.push_back({V, AssumptionCache::ExprResultIdx});
  64   };
  65
  66   auto AddAffectedVal = [&Affected](Value *V, unsigned Idx) {
  67     if (isa<Argument>(V) || isa<GlobalValue>(V) || isa<Instruction>(V)) {
  68       Affected.push_back({V, Idx});
  69     }
  70   };
  71
  72   for (unsigned Idx = 0; Idx != CI->getNumOperandBundles(); Idx++) {
  73     OperandBundleUse Bundle = CI->getOperandBundleAt(Idx);
  74     if (Bundle.getTagName() == "separate_storage") {
  75       assert(Bundle.Inputs.size() == 2 &&
  76              "separate_storage must have two args");
  77       AddAffectedVal(getUnderlyingObject(Bundle.Inputs[0]), Idx);
  78       AddAffectedVal(getUnderlyingObject(Bundle.Inputs[1]), Idx);
  79     } else if (Bundle.Inputs.size() > ABA_WasOn &&
  80                Bundle.getTagName() != IgnoreBundleTag)
  81       AddAffectedVal(Bundle.Inputs[ABA_WasOn], Idx);
  82   }
  83
  84   Value *Cond = CI->getArgOperand(0);
  85   findValuesAffectedByCondition(Cond, /*IsAssume=*/true, InsertAffected);
  86
  87   if (TTI) {
  88     const Value *Ptr;
  89     unsigned AS;
  90     std::tie(Ptr, AS) = TTI->getPredicatedAddrSpace(Cond);
  91     if (Ptr)
  92       AddAffectedVal(const_cast<Value *>(Ptr->stripInBoundsOffsets()),
  93                      AssumptionCache::ExprResultIdx);
  94   }
  95 }
  96
  97 void AssumptionCache::updateAffectedValues(AssumeInst *CI) {
  98   SmallVector<AssumptionCache::ResultElem, 16> Affected;
  99   findAffectedValues(CI, TTI, Affected);
 100
 101   for (auto &AV : Affected) {
 102     auto &AVV = getOrInsertAffectedValues(AV.Assume);
 103     if (llvm::none_of(AVV, [&](ResultElem &Elem) {
 104           return Elem.Assume == CI && Elem.Index == AV.Index;
 105         }))
 106       AVV.push_back({CI, AV.Index});
 107   }
 108 }
 109
 110 void AssumptionCache::unregisterAssumption(AssumeInst *CI) {
 111   SmallVector<AssumptionCache::ResultElem, 16> Affected;
 112   findAffectedValues(CI, TTI, Affected);
 113
 114   for (auto &AV : Affected) {
 115     auto AVI = AffectedValues.find_as(AV.Assume);
 116     if (AVI == AffectedValues.end())
 117       continue;
 118     bool Found = false;
 119     bool HasNonnull = false;
 120     for (ResultElem &Elem : AVI->second) {
 121       if (Elem.Assume == CI) {
 122         Found = true;
 123         Elem.Assume = nullptr;
 124       }
 125       HasNonnull |= !!Elem.Assume;
 126       if (HasNonnull && Found)
 127         break;
 128     }
 129     assert(Found && "already unregistered or incorrect cache state");
 130     if (!HasNonnull)
 131       AffectedValues.erase(AVI);
 132   }
 133
 134   llvm::erase(AssumeHandles, CI);
 135 }
 136
 137 void AssumptionCache::AffectedValueCallbackVH::deleted() {
 138   AC->AffectedValues.erase(getValPtr());
 139   // 'this' now dangles!
 140 }
 141
 142 void AssumptionCache::transferAffectedValuesInCache(Value *OV, Value *NV) {
 143   auto &NAVV = getOrInsertAffectedValues(NV);
 144   auto AVI = AffectedValues.find(OV);
 145   if (AVI == AffectedValues.end())
 146     return;
 147
 148   for (auto &A : AVI->second)
 149     if (!llvm::is_contained(NAVV, A))
 150       NAVV.push_back(A);
 151   AffectedValues.erase(OV);
 152 }
 153
 154 void AssumptionCache::AffectedValueCallbackVH::allUsesReplacedWith(Value *NV) {
 155   if (!isa<Instruction>(NV) && !isa<Argument>(NV))
 156     return;
 157
 158   // Any assumptions that affected this value now affect the new value.
 159
 160   AC->transferAffectedValuesInCache(getValPtr(), NV);
 161   // 'this' now might dangle! If the AffectedValues map was resized to add an
 162   // entry for NV then this object might have been destroyed in favor of some
 163   // copy in the grown map.
 164 }
 165
 166 void AssumptionCache::scanFunction() {
 167   assert(!Scanned && "Tried to scan the function twice!");
 168   assert(AssumeHandles.empty() && "Already have assumes when scanning!");
 169
 170   // Go through all instructions in all blocks, add all calls to @llvm.assume
 171   // to this cache.
 172   for (BasicBlock &B : F)
 173     for (Instruction &I : B)
 174       if (isa<AssumeInst>(&I))
 175         AssumeHandles.push_back({&I, ExprResultIdx});
 176
 177   // Mark the scan as complete.
 178   Scanned = true;
 179
 180   // Update affected values.
 181   for (auto &A : AssumeHandles)
 182     updateAffectedValues(cast<AssumeInst>(A));
 183 }
 184
 185 void AssumptionCache::registerAssumption(AssumeInst *CI) {
 186   // If we haven't scanned the function yet, just drop this assumption. It will
 187   // be found when we scan later.
 188   if (!Scanned)
 189     return;
 190
 191   AssumeHandles.push_back({CI, ExprResultIdx});
 192
 193 #ifndef NDEBUG
 194   assert(CI->getParent() &&
 195          "Cannot register @llvm.assume call not in a basic block");
 196   assert(&F == CI->getParent()->getParent() &&
 197          "Cannot register @llvm.assume call not in this function");
 198
 199   // We expect the number of assumptions to be small, so in an asserts build
 200   // check that we don't accumulate duplicates and that all assumptions point
 201   // to the same function.
 202   SmallPtrSet<Value *, 16> AssumptionSet;
 203   for (auto &VH : AssumeHandles) {
 204     if (!VH)
 205       continue;
 206
 207     assert(&F == cast<Instruction>(VH)->getParent()->getParent() &&
 208            "Cached assumption not inside this function!");
 209     assert(match(cast<CallInst>(VH), m_Intrinsic<Intrinsic::assume>()) &&
 210            "Cached something other than a call to @llvm.assume!");
 211     assert(AssumptionSet.insert(VH).second &&
 212            "Cache contains multiple copies of a call!");
 213   }
 214 #endif
 215
 216   updateAffectedValues(CI);
 217 }
 218
 219 AssumptionCache AssumptionAnalysis::run(Function &F,
 220                                         FunctionAnalysisManager &FAM) {
 221   auto &TTI = FAM.getResult<TargetIRAnalysis>(F);
 222   return AssumptionCache(F, &TTI);
 223 }
 224
 225 AnalysisKey AssumptionAnalysis::Key;
 226
 227 PreservedAnalyses AssumptionPrinterPass::run(Function &F,
 228                                              FunctionAnalysisManager &AM) {
 229   AssumptionCache &AC = AM.getResult<AssumptionAnalysis>(F);
 230
 231   OS << "Cached assumptions for function: " << F.getName() << "\n";
 232   for (auto &VH : AC.assumptions())
 233     if (VH)
 234       OS << "  " << *cast<CallInst>(VH)->getArgOperand(0) << "\n";
 235
 236   return PreservedAnalyses::all();
 237 }
 238
 239 void AssumptionCacheTracker::FunctionCallbackVH::deleted() {
 240   auto I = ACT->AssumptionCaches.find_as(cast<Function>(getValPtr()));
 241   if (I != ACT->AssumptionCaches.end())
 242     ACT->AssumptionCaches.erase(I);
 243   // 'this' now dangles!
 244 }
 245
 246 AssumptionCache &AssumptionCacheTracker::getAssumptionCache(Function &F) {
 247   // We probe the function map twice to try and avoid creating a value handle
 248   // around the function in common cases. This makes insertion a bit slower,
 249   // but if we have to insert we're going to scan the whole function so that
 250   // shouldn't matter.
 251   auto I = AssumptionCaches.find_as(&F);
 252   if (I != AssumptionCaches.end())
 253     return *I->second;
 254
 255   auto *TTIWP = getAnalysisIfAvailable<TargetTransformInfoWrapperPass>();
 256   auto *TTI = TTIWP ? &TTIWP->getTTI(F) : nullptr;
 257
 258   // Ok, build a new cache by scanning the function, insert it and the value
 259   // handle into our map, and return the newly populated cache.
 260   auto IP = AssumptionCaches.insert(std::make_pair(
 261       FunctionCallbackVH(&F, this), std::make_unique<AssumptionCache>(F, TTI)));
 262   assert(IP.second && "Scanning function already in the map?");
 263   return *IP.first->second;
 264 }
 265
 266 AssumptionCache *AssumptionCacheTracker::lookupAssumptionCache(Function &F) {
 267   auto I = AssumptionCaches.find_as(&F);
 268   if (I != AssumptionCaches.end())
 269     return I->second.get();
 270   return nullptr;
 271 }
 272
 273 void AssumptionCacheTracker::verifyAnalysis() const {
 274   // FIXME: In the long term the verifier should not be controllable with a
 275   // flag. We should either fix all passes to correctly update the assumption
 276   // cache and enable the verifier unconditionally or somehow arrange for the
 277   // assumption list to be updated automatically by passes.
 278   if (!VerifyAssumptionCache)
 279     return;
 280
 281   SmallPtrSet<const CallInst *, 4> AssumptionSet;
 282   for (const auto &I : AssumptionCaches) {
 283     for (auto &VH : I.second->assumptions())
 284       if (VH)
 285         AssumptionSet.insert(cast<CallInst>(VH));
 286
 287     for (const BasicBlock &B : cast<Function>(*I.first))
 288       for (const Instruction &II : B)
 289         if (match(&II, m_Intrinsic<Intrinsic::assume>()) &&
 290             !AssumptionSet.count(cast<CallInst>(&II)))
 291           report_fatal_error("Assumption in scanned function not in cache");
 292   }
 293 }
 294
 295 AssumptionCacheTracker::AssumptionCacheTracker() : ImmutablePass(ID) {
 296   initializeAssumptionCacheTrackerPass(*PassRegistry::getPassRegistry());
 297 }
 298
 299 AssumptionCacheTracker::~AssumptionCacheTracker() = default;
 300
 301 char AssumptionCacheTracker::ID = 0;
 302
 303 INITIALIZE_PASS(AssumptionCacheTracker, "assumption-cache-tracker",
 304                 "Assumption Cache Tracker", false, true)