[llvm-commits] [llvm] r138722 - in /llvm/trunk: lib/Analysis/ConstantFolding.cpp lib/Transforms/InstCombine/InstCombineCasts.cpp test/Transforms/InstCombine/cast.ll

[Duncan Sands]

Hi Nadav,

> --- lib/VMCore/Instructions.cpp	(revision 138427)
> +++ lib/VMCore/Instructions.cpp	(working copy)
> @@ -2114,10 +2114,12 @@
>
>    // If either of the casts are a bitcast from scalar to vector, disallow the
>    // merging.
> -  if ((firstOp == Instruction::BitCast &&
> +  // Bitcasts of A->B->A are okay.
> +  if ((SrcTy != DstTy) &&
> +      ((firstOp == Instruction::BitCast &&
>         isa<VectorType>(SrcTy) != isa<VectorType>(MidTy)) ||
>        (secondOp == Instruction::BitCast &&
> -       isa<VectorType>(MidTy) != isa<VectorType>(DstTy)))
> +       isa<VectorType>(MidTy) != isa<VectorType>(DstTy))))
>      return 0; // Disallowed

I think it would be better to say that it is OK if both instructions are
bitcasts.  The problematic case seems to be when one is a bitcast and the
other is not (PR7311).

Ciao, Duncan.

>
>    int ElimCase = CastResults[firstOp-Instruction::CastOpsBegin]