text: //===- AssumptionCache.cpp - Cache finding @llvm.assume calls -------------===//
  //
  // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  // See https://llvm.org/LICENSE.txt for license information.
  // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  //
  //===----------------------------------------------------------------------===//
  //
  // This file contains a pass that keeps track of @llvm.assume intrinsics in
  // the functions of a module.
  //
  //===----------------------------------------------------------------------===//
  
  #include "llvm/Analysis/AssumptionCache.h"
  #include "llvm/ADT/STLExtras.h"
  #include "llvm/ADT/SmallPtrSet.h"
  #include "llvm/ADT/SmallVector.h"
  #include "llvm/IR/BasicBlock.h"
  #include "llvm/IR/Function.h"
  #include "llvm/IR/InstrTypes.h"
  #include "llvm/IR/Instruction.h"
  #include "llvm/IR/Instructions.h"
  #include "llvm/IR/Intrinsics.h"
  #include "llvm/IR/PassManager.h"
  #include "llvm/IR/PatternMatch.h"
  #include "llvm/Pass.h"
  #include "llvm/Support/Casting.h"
  #include "llvm/Support/CommandLine.h"
  #include "llvm/Support/ErrorHandling.h"
  #include "llvm/Support/raw_ostream.h"
  #include <algorithm>
  #include <cassert>
  #include <utility>
  
  using namespace llvm;
  using namespace llvm::PatternMatch;
  
  static cl::opt<bool>
      VerifyAssumptionCache("verify-assumption-cache", cl::Hidden,
                            cl::desc("Enable verification of assumption cache"),
                            cl::init(false));
  
  SmallVector<WeakTrackingVH, 1> &
  AssumptionCache::getOrInsertAffectedValues(Value *V) {
    // Try using find_as first to avoid creating extra value handles just for the
    // purpose of doing the lookup.
    auto AVI = AffectedValues.find_as(V);
    if (AVI != AffectedValues.end())
      return AVI->second;
  
    auto AVIP = AffectedValues.insert(
        {AffectedValueCallbackVH(V, this), SmallVector<WeakTrackingVH, 1>()});
    return AVIP.first->second;
  }
  
  static void findAffectedValues(CallInst *CI,
                                 SmallVectorImpl<Value *> &Affected) {
    // Note: This code must be kept in-sync with the code in
    // computeKnownBitsFromAssume in ValueTracking.
  
    auto AddAffected = [&Affected](Value *V) {
      if (isa<Argument>(V)) {
        Affected.push_back(V);
      } else if (auto *I = dyn_cast<Instruction>(V)) {
        Affected.push_back(I);
  
        // Peek through unary operators to find the source of the condition.
        Value *Op;
        if (match(I, m_BitCast(m_Value(Op))) ||
            match(I, m_PtrToInt(m_Value(Op))) ||
            match(I, m_Not(m_Value(Op)))) {
          if (isa<Instruction>(Op) || isa<Argument>(Op))
            Affected.push_back(Op);
        }
      }
    };
  
    Value *Cond = CI->getArgOperand(0), *A, *B;
    AddAffected(Cond);
  
    CmpInst::Predicate Pred;
    if (match(Cond, m_ICmp(Pred, m_Value(A), m_Value(B)))) {
      AddAffected(A);
      AddAffected(B);
  
      if (Pred == ICmpInst::ICMP_EQ) {
        // For equality comparisons, we handle the case of bit inversion.
        auto AddAffectedFromEq = [&AddAffected](Value *V) {
          Value *A;
          if (match(V, m_Not(m_Value(A)))) {
            AddAffected(A);
            V = A;
          }
  
          Value *B;
          ConstantInt *C;
          // (A & B) or (A | B) or (A ^ B).
          if (match(V, m_BitwiseLogic(m_Value(A), m_Value(B)))) {
            AddAffected(A);
            AddAffected(B);
          // (A << C) or (A >>_s C) or (A >>_u C) where C is some constant.
          } else if (match(V, m_Shift(m_Value(A), m_ConstantInt(C)))) {
            AddAffected(A);
          }
        };
  
        AddAffectedFromEq(A);
        AddAffectedFromEq(B);
      }
    }
  }
  
  void AssumptionCache::updateAffectedValues(CallInst *CI) {
    SmallVector<Value *, 16> Affected;
    findAffectedValues(CI, Affected);
  
    for (auto &AV : Affected) {
      auto &AVV = getOrInsertAffectedValues(AV);
      if (std::find(AVV.begin(), AVV.end(), CI) == AVV.end())
        AVV.push_back(CI);
    }
  }
  
  void AssumptionCache::unregisterAssumption(CallInst *CI) {
    SmallVector<Value *, 16> Affected;
    findAffectedValues(CI, Affected);
  
    for (auto &AV : Affected) {
      auto AVI = AffectedValues.find_as(AV);
      if (AVI != AffectedValues.end())
        AffectedValues.erase(AVI);
    }
    remove_if(AssumeHandles, [CI](WeakTrackingVH &VH) { return CI == VH; });
  }
  
  void AssumptionCache::AffectedValueCallbackVH::deleted() {
    auto AVI = AC->AffectedValues.find(getValPtr());
    if (AVI != AC->AffectedValues.end())
      AC->AffectedValues.erase(AVI);
    // 'this' now dangles!
  }
  
  void AssumptionCache::transferAffectedValuesInCache(Value *OV, Value *NV) {
    auto &NAVV = getOrInsertAffectedValues(NV);
    auto AVI = AffectedValues.find(OV);
    if (AVI == AffectedValues.end())
      return;
  
    for (auto &A : AVI->second)
      if (std::find(NAVV.begin(), NAVV.end(), A) == NAVV.end())
        NAVV.push_back(A);
    AffectedValues.erase(OV);
  }
  
  void AssumptionCache::AffectedValueCallbackVH::allUsesReplacedWith(Value *NV) {
    if (!isa<Instruction>(NV) && !isa<Argument>(NV))
      return;
  
    // Any assumptions that affected this value now affect the new value.
  
    AC->transferAffectedValuesInCache(getValPtr(), NV);
    // 'this' now might dangle! If the AffectedValues map was resized to add an
    // entry for NV then this object might have been destroyed in favor of some
    // copy in the grown map.
  }
  
  void AssumptionCache::scanFunction() {
    assert(!Scanned && "Tried to scan the function twice!");
    assert(AssumeHandles.empty() && "Already have assumes when scanning!");
  
    // Go through all instructions in all blocks, add all calls to @llvm.assume
    // to this cache.
    for (BasicBlock &B : F)
      for (Instruction &II : B)
        if (match(&II, m_Intrinsic<Intrinsic::assume>()))
          AssumeHandles.push_back(&II);
  
    // Mark the scan as complete.
    Scanned = true;
  
    // Update affected values.
    for (auto &A : AssumeHandles)
      updateAffectedValues(cast<CallInst>(A));
  }
  
  void AssumptionCache::registerAssumption(CallInst *CI) {
    assert(match(CI, m_Intrinsic<Intrinsic::assume>()) &&
           "Registered call does not call @llvm.assume");
  
    // If we haven't scanned the function yet, just drop this assumption. It will
    // be found when we scan later.
    if (!Scanned)
      return;
  
    AssumeHandles.push_back(CI);
  
  #ifndef NDEBUG
    assert(CI->getParent() &&
           "Cannot register @llvm.assume call not in a basic block");
    assert(&F == CI->getParent()->getParent() &&
           "Cannot register @llvm.assume call not in this function");
  
    // We expect the number of assumptions to be small, so in an asserts build
    // check that we don't accumulate duplicates and that all assumptions point
    // to the same function.
    SmallPtrSet<Value *, 16> AssumptionSet;
    for (auto &VH : AssumeHandles) {
      if (!VH)
        continue;
  
      assert(&F == cast<Instruction>(VH)->getParent()->getParent() &&
             "Cached assumption not inside this function!");
      assert(match(cast<CallInst>(VH), m_Intrinsic<Intrinsic::assume>()) &&
             "Cached something other than a call to @llvm.assume!");
      assert(AssumptionSet.insert(VH).second &&
             "Cache contains multiple copies of a call!");
    }
  #endif
  
    updateAffectedValues(CI);
  }
  
  AnalysisKey AssumptionAnalysis::Key;
  
  PreservedAnalyses AssumptionPrinterPass::run(Function &F,
                                               FunctionAnalysisManager &AM) {
    AssumptionCache &AC = AM.getResult<AssumptionAnalysis>(F);
  
    OS << "Cached assumptions for function: " << F.getName() << "\n";
    for (auto &VH : AC.assumptions())
      if (VH)
        OS << "  " << *cast<CallInst>(VH)->getArgOperand(0) << "\n";
  
    return PreservedAnalyses::all();
  }
  
  void AssumptionCacheTracker::FunctionCallbackVH::deleted() {
    auto I = ACT->AssumptionCaches.find_as(cast<Function>(getValPtr()));
    if (I != ACT->AssumptionCaches.end())
      ACT->AssumptionCaches.erase(I);
    // 'this' now dangles!
  }
  
  AssumptionCache &AssumptionCacheTracker::getAssumptionCache(Function &F) {
    // We probe the function map twice to try and avoid creating a value handle
    // around the function in common cases. This makes insertion a bit slower,
    // but if we have to insert we're going to scan the whole function so that
    // shouldn't matter.
    auto I = AssumptionCaches.find_as(&F);
    if (I != AssumptionCaches.end())
      return *I->second;
  
    // Ok, build a new cache by scanning the function, insert it and the value
    // handle into our map, and return the newly populated cache.
    auto IP = AssumptionCaches.insert(std::make_pair(
        FunctionCallbackVH(&F, this), llvm::make_unique<AssumptionCache>(F)));
    assert(IP.second && "Scanning function already in the map?");
    return *IP.first->second;
  }
  
  AssumptionCache *AssumptionCacheTracker::lookupAssumptionCache(Function &F) {
    auto I = AssumptionCaches.find_as(&F);
    if (I != AssumptionCaches.end())
      return I->second.get();
    return nullptr;
  }
  
  void AssumptionCacheTracker::verifyAnalysis() const {
    // FIXME: In the long term the verifier should not be controllable with a
    // flag. We should either fix all passes to correctly update the assumption
    // cache and enable the verifier unconditionally or somehow arrange for the
    // assumption list to be updated automatically by passes.
    if (!VerifyAssumptionCache)
      return;
  
    SmallPtrSet<const CallInst *, 4> AssumptionSet;
    for (const auto &I : AssumptionCaches) {
      for (auto &VH : I.second->assumptions())
        if (VH)
          AssumptionSet.insert(cast<CallInst>(VH));
  
      for (const BasicBlock &B : cast<Function>(*I.first))
        for (const Instruction &II : B)
          if (match(&II, m_Intrinsic<Intrinsic::assume>()) &&
              !AssumptionSet.count(cast<CallInst>(&II)))
            report_fatal_error("Assumption in scanned function not in cache");
    }
  }
  
  AssumptionCacheTracker::AssumptionCacheTracker() : ImmutablePass(ID) {
    initializeAssumptionCacheTrackerPass(*PassRegistry::getPassRegistry());
  }
  
  AssumptionCacheTracker::~AssumptionCacheTracker() = default;
  
  char AssumptionCacheTracker::ID = 0;
  
  INITIALIZE_PASS(AssumptionCacheTracker, "assumption-cache-tracker",
                  "Assumption Cache Tracker", false, true)
  