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/AssumeBundleQueries.h"
  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/InitializePasses.h"
  28 #include "llvm/Pass.h"
  29 #include "llvm/Support/Casting.h"
  30 #include "llvm/Support/CommandLine.h"
  31 #include "llvm/Support/ErrorHandling.h"
  32 #include "llvm/Support/raw_ostream.h"
  33 #include <algorithm>
  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,
  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 AddAffected = [&Affected](Value *V, unsigned Idx =
  65                                                AssumptionCache::ExprResultIdx) {
  66     if (isa<Argument>(V)) {
  67       Affected.push_back({V, Idx});
  68     } else if (auto *I = dyn_cast<Instruction>(V)) {
  69       Affected.push_back({I, Idx});
  70
  71       // Peek through unary operators to find the source of the condition.
  72       Value *Op;
  73       if (match(I, m_BitCast(m_Value(Op))) ||
  74           match(I, m_PtrToInt(m_Value(Op))) || match(I, m_Not(m_Value(Op)))) {
  75         if (isa<Instruction>(Op) || isa<Argument>(Op))
  76           Affected.push_back({Op, Idx});
  77       }
  78     }
  79   };
  80
  81   for (unsigned Idx = 0; Idx != CI->getNumOperandBundles(); Idx++) {
  82     if (CI->getOperandBundleAt(Idx).Inputs.size() > ABA_WasOn &&
  83         CI->getOperandBundleAt(Idx).getTagName() != IgnoreBundleTag)
  84       AddAffected(CI->getOperandBundleAt(Idx).Inputs[ABA_WasOn], Idx);
  85   }
  86
  87   Value *Cond = CI->getArgOperand(0), *A, *B;
  88   AddAffected(Cond);
  89
  90   CmpInst::Predicate Pred;
  91   if (match(Cond, m_ICmp(Pred, m_Value(A), m_Value(B)))) {
  92     AddAffected(A);
  93     AddAffected(B);
  94
  95     if (Pred == ICmpInst::ICMP_EQ) {
  96       // For equality comparisons, we handle the case of bit inversion.
  97       auto AddAffectedFromEq = [&AddAffected](Value *V) {
  98         Value *A;
  99         if (match(V, m_Not(m_Value(A)))) {
 100           AddAffected(A);
 101           V = A;
 102         }
 103
 104         Value *B;
 105         // (A & B) or (A | B) or (A ^ B).
 106         if (match(V, m_BitwiseLogic(m_Value(A), m_Value(B)))) {
 107           AddAffected(A);
 108           AddAffected(B);
 109         // (A << C) or (A >>_s C) or (A >>_u C) where C is some constant.
 110         } else if (match(V, m_Shift(m_Value(A), m_ConstantInt()))) {
 111           AddAffected(A);
 112         }
 113       };
 114
 115       AddAffectedFromEq(A);
 116       AddAffectedFromEq(B);
 117     }
 118
 119     Value *X;
 120     // Handle (A + C1) u< C2, which is the canonical form of A > C3 && A < C4,
 121     // and recognized by LVI at least.
 122     if (Pred == ICmpInst::ICMP_ULT &&
 123         match(A, m_Add(m_Value(X), m_ConstantInt())) &&
 124         match(B, m_ConstantInt()))
 125       AddAffected(X);
 126   }
 127 }
 128
 129 void AssumptionCache::updateAffectedValues(AssumeInst *CI) {
 130   SmallVector<AssumptionCache::ResultElem, 16> Affected;
 131   findAffectedValues(CI, Affected);
 132
 133   for (auto &AV : Affected) {
 134     auto &AVV = getOrInsertAffectedValues(AV.Assume);
 135     if (std::find_if(AVV.begin(), AVV.end(), [&](ResultElem &Elem) {
 136           return Elem.Assume == CI && Elem.Index == AV.Index;
 137         }) == AVV.end())
 138       AVV.push_back({CI, AV.Index});
 139   }
 140 }
 141
 142 void AssumptionCache::unregisterAssumption(AssumeInst *CI) {
 143   SmallVector<AssumptionCache::ResultElem, 16> Affected;
 144   findAffectedValues(CI, Affected);
 145
 146   for (auto &AV : Affected) {
 147     auto AVI = AffectedValues.find_as(AV.Assume);
 148     if (AVI == AffectedValues.end())
 149       continue;
 150     bool Found = false;
 151     bool HasNonnull = false;
 152     for (ResultElem &Elem : AVI->second) {
 153       if (Elem.Assume == CI) {
 154         Found = true;
 155         Elem.Assume = nullptr;
 156       }
 157       HasNonnull |= !!Elem.Assume;
 158       if (HasNonnull && Found)
 159         break;
 160     }
 161     assert(Found && "already unregistered or incorrect cache state");
 162     if (!HasNonnull)
 163       AffectedValues.erase(AVI);
 164   }
 165
 166   erase_value(AssumeHandles, CI);
 167 }
 168
 169 void AssumptionCache::AffectedValueCallbackVH::deleted() {
 170   AC->AffectedValues.erase(getValPtr());
 171   // 'this' now dangles!
 172 }
 173
 174 void AssumptionCache::transferAffectedValuesInCache(Value *OV, Value *NV) {
 175   auto &NAVV = getOrInsertAffectedValues(NV);
 176   auto AVI = AffectedValues.find(OV);
 177   if (AVI == AffectedValues.end())
 178     return;
 179
 180   for (auto &A : AVI->second)
 181     if (!llvm::is_contained(NAVV, A))
 182       NAVV.push_back(A);
 183   AffectedValues.erase(OV);
 184 }
 185
 186 void AssumptionCache::AffectedValueCallbackVH::allUsesReplacedWith(Value *NV) {
 187   if (!isa<Instruction>(NV) && !isa<Argument>(NV))
 188     return;
 189
 190   // Any assumptions that affected this value now affect the new value.
 191
 192   AC->transferAffectedValuesInCache(getValPtr(), NV);
 193   // 'this' now might dangle! If the AffectedValues map was resized to add an
 194   // entry for NV then this object might have been destroyed in favor of some
 195   // copy in the grown map.
 196 }
 197
 198 void AssumptionCache::scanFunction() {
 199   assert(!Scanned && "Tried to scan the function twice!");
 200   assert(AssumeHandles.empty() && "Already have assumes when scanning!");
 201
 202   // Go through all instructions in all blocks, add all calls to @llvm.assume
 203   // to this cache.
 204   for (BasicBlock &B : F)
 205     for (Instruction &I : B)
 206       if (isa<AssumeInst>(&I))
 207         AssumeHandles.push_back({&I, ExprResultIdx});
 208
 209   // Mark the scan as complete.
 210   Scanned = true;
 211
 212   // Update affected values.
 213   for (auto &A : AssumeHandles)
 214     updateAffectedValues(cast<AssumeInst>(A));
 215 }
 216
 217 void AssumptionCache::registerAssumption(AssumeInst *CI) {
 218   // If we haven't scanned the function yet, just drop this assumption. It will
 219   // be found when we scan later.
 220   if (!Scanned)
 221     return;
 222
 223   AssumeHandles.push_back({CI, ExprResultIdx});
 224
 225 #ifndef NDEBUG
 226   assert(CI->getParent() &&
 227          "Cannot register @llvm.assume call not in a basic block");
 228   assert(&F == CI->getParent()->getParent() &&
 229          "Cannot register @llvm.assume call not in this function");
 230
 231   // We expect the number of assumptions to be small, so in an asserts build
 232   // check that we don't accumulate duplicates and that all assumptions point
 233   // to the same function.
 234   SmallPtrSet<Value *, 16> AssumptionSet;
 235   for (auto &VH : AssumeHandles) {
 236     if (!VH)
 237       continue;
 238
 239     assert(&F == cast<Instruction>(VH)->getParent()->getParent() &&
 240            "Cached assumption not inside this function!");
 241     assert(match(cast<CallInst>(VH), m_Intrinsic<Intrinsic::assume>()) &&
 242            "Cached something other than a call to @llvm.assume!");
 243     assert(AssumptionSet.insert(VH).second &&
 244            "Cache contains multiple copies of a call!");
 245   }
 246 #endif
 247
 248   updateAffectedValues(CI);
 249 }
 250
 251 AnalysisKey AssumptionAnalysis::Key;
 252
 253 PreservedAnalyses AssumptionPrinterPass::run(Function &F,
 254                                              FunctionAnalysisManager &AM) {
 255   AssumptionCache &AC = AM.getResult<AssumptionAnalysis>(F);
 256
 257   OS << "Cached assumptions for function: " << F.getName() << "\n";
 258   for (auto &VH : AC.assumptions())
 259     if (VH)
 260       OS << "  " << *cast<CallInst>(VH)->getArgOperand(0) << "\n";
 261
 262   return PreservedAnalyses::all();
 263 }
 264
 265 void AssumptionCacheTracker::FunctionCallbackVH::deleted() {
 266   auto I = ACT->AssumptionCaches.find_as(cast<Function>(getValPtr()));
 267   if (I != ACT->AssumptionCaches.end())
 268     ACT->AssumptionCaches.erase(I);
 269   // 'this' now dangles!
 270 }
 271
 272 AssumptionCache &AssumptionCacheTracker::getAssumptionCache(Function &F) {
 273   // We probe the function map twice to try and avoid creating a value handle
 274   // around the function in common cases. This makes insertion a bit slower,
 275   // but if we have to insert we're going to scan the whole function so that
 276   // shouldn't matter.
 277   auto I = AssumptionCaches.find_as(&F);
 278   if (I != AssumptionCaches.end())
 279     return *I->second;
 280
 281   // Ok, build a new cache by scanning the function, insert it and the value
 282   // handle into our map, and return the newly populated cache.
 283   auto IP = AssumptionCaches.insert(std::make_pair(
 284       FunctionCallbackVH(&F, this), std::make_unique<AssumptionCache>(F)));
 285   assert(IP.second && "Scanning function already in the map?");
 286   return *IP.first->second;
 287 }
 288
 289 AssumptionCache *AssumptionCacheTracker::lookupAssumptionCache(Function &F) {
 290   auto I = AssumptionCaches.find_as(&F);
 291   if (I != AssumptionCaches.end())
 292     return I->second.get();
 293   return nullptr;
 294 }
 295
 296 void AssumptionCacheTracker::verifyAnalysis() const {
 297   // FIXME: In the long term the verifier should not be controllable with a
 298   // flag. We should either fix all passes to correctly update the assumption
 299   // cache and enable the verifier unconditionally or somehow arrange for the
 300   // assumption list to be updated automatically by passes.
 301   if (!VerifyAssumptionCache)
 302     return;
 303
 304   SmallPtrSet<const CallInst *, 4> AssumptionSet;
 305   for (const auto &I : AssumptionCaches) {
 306     for (auto &VH : I.second->assumptions())
 307       if (VH)
 308         AssumptionSet.insert(cast<CallInst>(VH));
 309
 310     for (const BasicBlock &B : cast<Function>(*I.first))
 311       for (const Instruction &II : B)
 312         if (match(&II, m_Intrinsic<Intrinsic::assume>()) &&
 313             !AssumptionSet.count(cast<CallInst>(&II)))
 314           report_fatal_error("Assumption in scanned function not in cache");
 315   }
 316 }
 317
 318 AssumptionCacheTracker::AssumptionCacheTracker() : ImmutablePass(ID) {
 319   initializeAssumptionCacheTrackerPass(*PassRegistry::getPassRegistry());
 320 }
 321
 322 AssumptionCacheTracker::~AssumptionCacheTracker() = default;
 323
 324 char AssumptionCacheTracker::ID = 0;
 325
 326 INITIALIZE_PASS(AssumptionCacheTracker, "assumption-cache-tracker",
 327                 "Assumption Cache Tracker", false, true)