C++ Attributes::hasAttribute方法代码示例

bool llvm::isInTailCallPosition(SelectionDAG &DAG, SDNode *Node,
                                SDValue &Chain, const TargetLowering &TLI) {
  const Function *F = DAG.getMachineFunction().getFunction();

  // Conservatively require the attributes of the call to match those of
  // the return. Ignore noalias because it doesn't affect the call sequence.
  Attributes CallerRetAttr = F->getAttributes().getRetAttributes();
  if (AttrBuilder(CallerRetAttr)
      .removeAttribute(Attributes::NoAlias).hasAttributes())
    return false;

  // It's not safe to eliminate the sign / zero extension of the return value.
  if (CallerRetAttr.hasAttribute(Attributes::ZExt) ||
      CallerRetAttr.hasAttribute(Attributes::SExt))
    return false;

  // Check if the only use is a function return node.
  return TLI.isUsedByReturnOnly(Node, Chain);
}

/// DupRetToEnableTailCallOpts - Look for opportunities to duplicate return
/// instructions to the predecessor to enable tail call optimizations. The
/// case it is currently looking for is:
/// @code
/// bb0:
///   %tmp0 = tail call i32 @f0()
///   br label %return
/// bb1:
///   %tmp1 = tail call i32 @f1()
///   br label %return
/// bb2:
///   %tmp2 = tail call i32 @f2()
///   br label %return
/// return:
///   %retval = phi i32 [ %tmp0, %bb0 ], [ %tmp1, %bb1 ], [ %tmp2, %bb2 ]
///   ret i32 %retval
/// @endcode
///
/// =>
///
/// @code
/// bb0:
///   %tmp0 = tail call i32 @f0()
///   ret i32 %tmp0
/// bb1:
///   %tmp1 = tail call i32 @f1()
///   ret i32 %tmp1
/// bb2:
///   %tmp2 = tail call i32 @f2()
///   ret i32 %tmp2
/// @endcode
bool CodeGenPrepare::DupRetToEnableTailCallOpts(ReturnInst *RI) {
  if (!TLI)
    return false;

  PHINode *PN = 0;
  BitCastInst *BCI = 0;
  Value *V = RI->getReturnValue();
  if (V) {
    BCI = dyn_cast<BitCastInst>(V);
    if (BCI)
      V = BCI->getOperand(0);

    PN = dyn_cast<PHINode>(V);
    if (!PN)
      return false;
  }

  BasicBlock *BB = RI->getParent();
  if (PN && PN->getParent() != BB)
    return false;

  // It's not safe to eliminate the sign / zero extension of the return value.
  // See llvm::isInTailCallPosition().
  const Function *F = BB->getParent();
  Attributes CallerRetAttr = F->getAttributes().getRetAttributes();
  if (CallerRetAttr.hasAttribute(Attributes::ZExt) ||
      CallerRetAttr.hasAttribute(Attributes::SExt))
    return false;

  // Make sure there are no instructions between the PHI and return, or that the
  // return is the first instruction in the block.
  if (PN) {
    BasicBlock::iterator BI = BB->begin();
    do { ++BI; } while (isa<DbgInfoIntrinsic>(BI));
    if (&*BI == BCI)
      // Also skip over the bitcast.
      ++BI;
    if (&*BI != RI)
      return false;
  } else {
    BasicBlock::iterator BI = BB->begin();
    while (isa<DbgInfoIntrinsic>(BI)) ++BI;
    if (&*BI != RI)
      return false;
  }

  /// Only dup the ReturnInst if the CallInst is likely to be emitted as a tail
  /// call.
  SmallVector<CallInst*, 4> TailCalls;
  if (PN) {
    for (unsigned I = 0, E = PN->getNumIncomingValues(); I != E; ++I) {
      CallInst *CI = dyn_cast<CallInst>(PN->getIncomingValue(I));
      // Make sure the phi value is indeed produced by the tail call.
      if (CI && CI->hasOneUse() && CI->getParent() == PN->getIncomingBlock(I) &&
          TLI->mayBeEmittedAsTailCall(CI))
        TailCalls.push_back(CI);
    }
  } else {
    SmallPtrSet<BasicBlock*, 4> VisitedBBs;
    for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE; ++PI) {
      if (!VisitedBBs.insert(*PI))
        continue;

      BasicBlock::InstListType &InstList = (*PI)->getInstList();
      BasicBlock::InstListType::reverse_iterator RI = InstList.rbegin();
      BasicBlock::InstListType::reverse_iterator RE = InstList.rend();
      do { ++RI; } while (RI != RE && isa<DbgInfoIntrinsic>(&*RI));
      if (RI == RE)
        continue;
//.........这里部分代码省略.........