C++ CallInst::doesNotAccessMemory方法代码示例

bool IRTranslator::translateCall(const CallInst &CI) {
  auto TII = MIRBuilder.getMF().getTarget().getIntrinsicInfo();
  const Function &F = *CI.getCalledFunction();
  Intrinsic::ID ID = F.getIntrinsicID();
  if (TII && ID == Intrinsic::not_intrinsic)
    ID = static_cast<Intrinsic::ID>(TII->getIntrinsicID(&F));

  assert(ID != Intrinsic::not_intrinsic && "FIXME: support real calls");

  // Need types (starting with return) & args.
  SmallVector<LLT, 4> Tys;
  Tys.emplace_back(*CI.getType());
  for (auto &Arg : CI.arg_operands())
    Tys.emplace_back(*Arg->getType());

  unsigned Res = CI.getType()->isVoidTy() ? 0 : getOrCreateVReg(CI);
  MachineInstrBuilder MIB =
      MIRBuilder.buildIntrinsic(Tys, ID, Res, !CI.doesNotAccessMemory());

  for (auto &Arg : CI.arg_operands()) {
    if (ConstantInt *CI = dyn_cast<ConstantInt>(Arg))
      MIB.addImm(CI->getSExtValue());
    else
      MIB.addUse(getOrCreateVReg(*Arg));
  }
  return true;
}

bool ScopDetection::isValidCallInst(CallInst &CI) {
  if (CI.mayHaveSideEffects() || CI.doesNotReturn())
    return false;

  if (CI.doesNotAccessMemory())
    return true;

  Function *CalledFunction = CI.getCalledFunction();

  // Indirect calls are not supported.
  if (CalledFunction == 0)
    return false;

  // TODO: Intrinsics.
  return false;
}

bool ScopDetection::isValidCallInst(CallInst &CI) {
  if (CI.doesNotReturn())
    return false;

  if (CI.doesNotAccessMemory())
    return true;

  Function *CalledFunction = CI.getCalledFunction();

  // Indirect calls are not supported.
  if (CalledFunction == 0)
    return false;

  // Check if we can handle the intrinsic call.
  if (auto *IT = dyn_cast<IntrinsicInst>(&CI)) {
    switch (IT->getIntrinsicID()) {
    // Lifetime markers are supported/ignored.
    case llvm::Intrinsic::lifetime_start:
    case llvm::Intrinsic::lifetime_end:
    // Invariant markers are supported/ignored.
    case llvm::Intrinsic::invariant_start:
    case llvm::Intrinsic::invariant_end:
    // Some misc annotations are supported/ignored.
    case llvm::Intrinsic::var_annotation:
    case llvm::Intrinsic::ptr_annotation:
    case llvm::Intrinsic::annotation:
    case llvm::Intrinsic::donothing:
    case llvm::Intrinsic::assume:
    case llvm::Intrinsic::expect:
      return true;
    default:
      // Other intrinsics which may access the memory are not yet supported.
      break;
    }
  }

  return false;
}

static bool markTails(Function &F, bool &AllCallsAreTailCalls) {
  if (F.callsFunctionThatReturnsTwice())
    return false;
  AllCallsAreTailCalls = true;

  // The local stack holds all alloca instructions and all byval arguments.
  AllocaDerivedValueTracker Tracker;
  for (Argument &Arg : F.args()) {
    if (Arg.hasByValAttr())
      Tracker.walk(&Arg);
  }
  for (auto &BB : F) {
    for (auto &I : BB)
      if (AllocaInst *AI = dyn_cast<AllocaInst>(&I))
        Tracker.walk(AI);
  }

  bool Modified = false;

  // Track whether a block is reachable after an alloca has escaped. Blocks that
  // contain the escaping instruction will be marked as being visited without an
  // escaped alloca, since that is how the block began.
  enum VisitType {
    UNVISITED,
    UNESCAPED,
    ESCAPED
  };
  DenseMap<BasicBlock *, VisitType> Visited;

  // We propagate the fact that an alloca has escaped from block to successor.
  // Visit the blocks that are propagating the escapedness first. To do this, we
  // maintain two worklists.
  SmallVector<BasicBlock *, 32> WorklistUnescaped, WorklistEscaped;

  // We may enter a block and visit it thinking that no alloca has escaped yet,
  // then see an escape point and go back around a loop edge and come back to
  // the same block twice. Because of this, we defer setting tail on calls when
  // we first encounter them in a block. Every entry in this list does not
  // statically use an alloca via use-def chain analysis, but may find an alloca
  // through other means if the block turns out to be reachable after an escape
  // point.
  SmallVector<CallInst *, 32> DeferredTails;

  BasicBlock *BB = &F.getEntryBlock();
  VisitType Escaped = UNESCAPED;
  do {
    for (auto &I : *BB) {
      if (Tracker.EscapePoints.count(&I))
        Escaped = ESCAPED;

      CallInst *CI = dyn_cast<CallInst>(&I);
      if (!CI || CI->isTailCall())
        continue;

      bool IsNoTail = CI->isNoTailCall() || CI->hasOperandBundles();

      if (!IsNoTail && CI->doesNotAccessMemory()) {
        // A call to a readnone function whose arguments are all things computed
        // outside this function can be marked tail. Even if you stored the
        // alloca address into a global, a readnone function can't load the
        // global anyhow.
        //
        // Note that this runs whether we know an alloca has escaped or not. If
        // it has, then we can't trust Tracker.AllocaUsers to be accurate.
        bool SafeToTail = true;
        for (auto &Arg : CI->arg_operands()) {
          if (isa<Constant>(Arg.getUser()))
            continue;
          if (Argument *A = dyn_cast<Argument>(Arg.getUser()))
            if (!A->hasByValAttr())
              continue;
          SafeToTail = false;
          break;
        }
        if (SafeToTail) {
          emitOptimizationRemark(
              F.getContext(), "tailcallelim", F, CI->getDebugLoc(),
              "marked this readnone call a tail call candidate");
          CI->setTailCall();
          Modified = true;
          continue;
        }
      }

      if (!IsNoTail && Escaped == UNESCAPED && !Tracker.AllocaUsers.count(CI)) {
        DeferredTails.push_back(CI);
      } else {
        AllCallsAreTailCalls = false;
      }
    }

    for (auto *SuccBB : make_range(succ_begin(BB), succ_end(BB))) {
      auto &State = Visited[SuccBB];
      if (State < Escaped) {
        State = Escaped;
        if (State == ESCAPED)
          WorklistEscaped.push_back(SuccBB);
        else
          WorklistUnescaped.push_back(SuccBB);
      }
//.........这里部分代码省略.........