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