C++ arg_iterator::hasNoCaptureAttr方法代码示例

/// AddNoCaptureAttrs - Deduce nocapture attributes for the SCC.
bool FunctionAttrs::AddNoCaptureAttrs(const CallGraphSCC &SCC) {
  bool Changed = false;

  // Check each function in turn, determining which pointer arguments are not
  // captured.
  for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
    Function *F = (*I)->getFunction();

    if (F == 0)
      // External node - skip it;
      continue;

    // Definitions with weak linkage may be overridden at linktime with
    // something that writes memory, so treat them like declarations.
    if (F->isDeclaration() || F->mayBeOverridden())
      continue;

    for (Function::arg_iterator A = F->arg_begin(), E = F->arg_end(); A!=E; ++A)
      if (A->getType()->isPointerTy() && !A->hasNoCaptureAttr() &&
          !PointerMayBeCaptured(A, true, /*StoreCaptures=*/false)) {
        A->addAttr(Attribute::NoCapture);
        ++NumNoCapture;
        Changed = true;
      }
  }

  return Changed;
}

/// Deduce nocapture attributes for the SCC.
static bool addArgumentAttrs(const SCCNodeSet &SCCNodes) {
  bool Changed = false;

  ArgumentGraph AG;

  // Check each function in turn, determining which pointer arguments are not
  // captured.
  for (Function *F : SCCNodes) {
    // We can infer and propagate function attributes only when we know that the
    // definition we'll get at link time is *exactly* the definition we see now.
    // For more details, see GlobalValue::mayBeDerefined.
    if (!F->hasExactDefinition())
      continue;

    Changed |= addArgumentAttrsFromCallsites(*F);

    // Functions that are readonly (or readnone) and nounwind and don't return
    // a value can't capture arguments. Don't analyze them.
    if (F->onlyReadsMemory() && F->doesNotThrow() &&
        F->getReturnType()->isVoidTy()) {
      for (Function::arg_iterator A = F->arg_begin(), E = F->arg_end(); A != E;
           ++A) {
        if (A->getType()->isPointerTy() && !A->hasNoCaptureAttr()) {
          A->addAttr(Attribute::NoCapture);
          ++NumNoCapture;
          Changed = true;
        }
      }
      continue;
    }

    for (Function::arg_iterator A = F->arg_begin(), E = F->arg_end(); A != E;
         ++A) {
      if (!A->getType()->isPointerTy())
        continue;
      bool HasNonLocalUses = false;
      if (!A->hasNoCaptureAttr()) {
        ArgumentUsesTracker Tracker(SCCNodes);
        PointerMayBeCaptured(&*A, &Tracker);
        if (!Tracker.Captured) {
          if (Tracker.Uses.empty()) {
            // If it's trivially not captured, mark it nocapture now.
            A->addAttr(Attribute::NoCapture);
            ++NumNoCapture;
            Changed = true;
          } else {
            // If it's not trivially captured and not trivially not captured,
            // then it must be calling into another function in our SCC. Save
            // its particulars for Argument-SCC analysis later.
            ArgumentGraphNode *Node = AG[&*A];
            for (Argument *Use : Tracker.Uses) {
              Node->Uses.push_back(AG[Use]);
              if (Use != &*A)
                HasNonLocalUses = true;
            }
          }
        }
        // Otherwise, it's captured. Don't bother doing SCC analysis on it.
      }
      if (!HasNonLocalUses && !A->onlyReadsMemory()) {
        // Can we determine that it's readonly/readnone without doing an SCC?
        // Note that we don't allow any calls at all here, or else our result
        // will be dependent on the iteration order through the functions in the
        // SCC.
        SmallPtrSet<Argument *, 8> Self;
        Self.insert(&*A);
        Attribute::AttrKind R = determinePointerReadAttrs(&*A, Self);
        if (R != Attribute::None) {
          A->addAttr(R);
          Changed = true;
          R == Attribute::ReadOnly ? ++NumReadOnlyArg : ++NumReadNoneArg;
        }
      }
    }
  }

  // The graph we've collected is partial because we stopped scanning for
  // argument uses once we solved the argument trivially. These partial nodes
  // show up as ArgumentGraphNode objects with an empty Uses list, and for
  // these nodes the final decision about whether they capture has already been
  // made.  If the definition doesn't have a 'nocapture' attribute by now, it
  // captures.

  for (scc_iterator<ArgumentGraph *> I = scc_begin(&AG); !I.isAtEnd(); ++I) {
    const std::vector<ArgumentGraphNode *> &ArgumentSCC = *I;
    if (ArgumentSCC.size() == 1) {
      if (!ArgumentSCC[0]->Definition)
        continue; // synthetic root node

      // eg. "void f(int* x) { if (...) f(x); }"
      if (ArgumentSCC[0]->Uses.size() == 1 &&
          ArgumentSCC[0]->Uses[0] == ArgumentSCC[0]) {
        Argument *A = ArgumentSCC[0]->Definition;
        A->addAttr(Attribute::NoCapture);
        ++NumNoCapture;
        Changed = true;
      }
      continue;
    }
//.........这里部分代码省略.........

/// AddNoCaptureAttrs - Deduce nocapture attributes for the SCC.
bool FunctionAttrs::AddNoCaptureAttrs(const CallGraphSCC &SCC) {
  bool Changed = false;

  SmallPtrSet<Function*, 8> SCCNodes;

  // Fill SCCNodes with the elements of the SCC.  Used for quickly
  // looking up whether a given CallGraphNode is in this SCC.
  for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
    Function *F = (*I)->getFunction();
    if (F && !F->isDeclaration() && !F->mayBeOverridden())
      SCCNodes.insert(F);
  }

  ArgumentGraph AG;

  // Check each function in turn, determining which pointer arguments are not
  // captured.
  for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
    Function *F = (*I)->getFunction();

    if (F == 0)
      // External node - only a problem for arguments that we pass to it.
      continue;

    // Definitions with weak linkage may be overridden at linktime with
    // something that captures pointers, so treat them like declarations.
    if (F->isDeclaration() || F->mayBeOverridden())
      continue;

    // Functions that are readonly (or readnone) and nounwind and don't return
    // a value can't capture arguments. Don't analyze them.
    if (F->onlyReadsMemory() && F->doesNotThrow() &&
        F->getReturnType()->isVoidTy()) {
      for (Function::arg_iterator A = F->arg_begin(), E = F->arg_end();
           A != E; ++A) {
        if (A->getType()->isPointerTy() && !A->hasNoCaptureAttr()) {
          A->addAttr(Attribute::NoCapture);
          ++NumNoCapture;
          Changed = true;
        }
      }
      continue;
    }

    for (Function::arg_iterator A = F->arg_begin(), E = F->arg_end(); A!=E; ++A)
      if (A->getType()->isPointerTy() && !A->hasNoCaptureAttr()) {
        ArgumentUsesTracker Tracker(SCCNodes);
        PointerMayBeCaptured(A, &Tracker);
        if (!Tracker.Captured) {
          if (Tracker.Uses.empty()) {
            // If it's trivially not captured, mark it nocapture now.
            A->addAttr(Attribute::NoCapture);
            ++NumNoCapture;
            Changed = true;
          } else {
            // If it's not trivially captured and not trivially not captured,
            // then it must be calling into another function in our SCC. Save
            // its particulars for Argument-SCC analysis later.
            ArgumentGraphNode *Node = AG[A];
            for (SmallVectorImpl<Argument*>::iterator UI = Tracker.Uses.begin(),
                   UE = Tracker.Uses.end(); UI != UE; ++UI)
              Node->Uses.push_back(AG[*UI]);
          }
        }
        // Otherwise, it's captured. Don't bother doing SCC analysis on it.
      }
  }

  // The graph we've collected is partial because we stopped scanning for
  // argument uses once we solved the argument trivially. These partial nodes
  // show up as ArgumentGraphNode objects with an empty Uses list, and for
  // these nodes the final decision about whether they capture has already been
  // made.  If the definition doesn't have a 'nocapture' attribute by now, it
  // captures.

  for (scc_iterator<ArgumentGraph*> I = scc_begin(&AG), E = scc_end(&AG);
       I != E; ++I) {
    std::vector<ArgumentGraphNode*> &ArgumentSCC = *I;
    if (ArgumentSCC.size() == 1) {
      if (!ArgumentSCC[0]->Definition) continue;  // synthetic root node

      // eg. "void f(int* x) { if (...) f(x); }"
      if (ArgumentSCC[0]->Uses.size() == 1 &&
          ArgumentSCC[0]->Uses[0] == ArgumentSCC[0]) {
        ArgumentSCC[0]->Definition->addAttr(Attribute::NoCapture);
        ++NumNoCapture;
        Changed = true;
      }
      continue;
    }

    bool SCCCaptured = false;
    for (std::vector<ArgumentGraphNode*>::iterator I = ArgumentSCC.begin(),
           E = ArgumentSCC.end(); I != E && !SCCCaptured; ++I) {
      ArgumentGraphNode *Node = *I;
      if (Node->Uses.empty()) {
        if (!Node->Definition->hasNoCaptureAttr())
          SCCCaptured = true;
      }
//.........这里部分代码省略.........