[llvm-commits] [llvm] r128197 - in /llvm/trunk: lib/Transforms/Scalar/CodeGenPrepare.cpp test/CodeGen/X86/tailcall-returndup-void.ll

[Frits van Bommel]

On Thu, Mar 24, 2011 at 5:52 AM, Cameron Zwarich <zwarich at apple.com> wrote:
> +  // 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 != RI)
> +      return false;
> +  } else {
> +    if (&*BB->begin() != RI)
> +      return false;

'void' returns don't get to ignore debug intrinsics?

> +  }
>
>   /// Only dup the ReturnInst if the CallInst is likely to be emitted as a tail
>   /// call.
>   SmallVector<CallInst*, 4> TailCalls;
> -  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);
> +  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();
> +      if (++RI == RE)
> +        continue;
> +      CallInst *CI = dyn_cast<CallInst>(&*RI);
> +      if (CI && CI->getType()->isVoidTy() && TLI->mayBeEmittedAsTailCall(CI))
> +        TailCalls.push_back(CI);

I don't think the 'isVoidTy()' check is necessary -- since void
functions don't return a value they shouldn't care about what value
their tail-callee returns (as long as it doesn't use sret).
For instance, a void function calling an int function should still be
able to use a tail call if the other conditions are met.