[llvm-commits] [llvm] r138756 - in /llvm/trunk: lib/Analysis/ConstantFolding.cpp lib/Transforms/InstCombine/InstCombineCasts.cpp lib/VMCore/Instructions.cpp test/Transforms/InstCombine/cast.ll

[Duncan Sands]

Hi Nadav,

> --- llvm/trunk/lib/VMCore/Instructions.cpp (original)
> +++ llvm/trunk/lib/VMCore/Instructions.cpp Mon Aug 29 14:58:36 2011
> @@ -2059,8 +2059,7 @@
>   /// If no such cast is permited, the function returns 0.
>   unsigned CastInst::isEliminableCastPair(
>     Instruction::CastOps firstOp, Instruction::CastOps secondOp,
> -  Type *SrcTy, Type *MidTy, Type *DstTy, Type *IntPtrTy)
> -{
> +  Type *SrcTy, Type *MidTy, Type *DstTy, Type *IntPtrTy) {
>     // Define the 144 possibilities for these two cast instructions. The values
>     // in this matrix determine what to do in a given situation and select the
>     // case in the switch below.  The rows correspond to firstOp, the columns
> @@ -2113,12 +2112,16 @@
>     };
>
>     // If either of the casts are a bitcast from scalar to vector, disallow the
> -  // merging.
> -  if ((firstOp == Instruction::BitCast&&
> -       isa<VectorType>(SrcTy) != isa<VectorType>(MidTy)) ||
> -      (secondOp == Instruction::BitCast&&
> -       isa<VectorType>(MidTy) != isa<VectorType>(DstTy)))
> -    return 0; // Disallowed
> +  // merging. However, bitcast of A->B->A are allowed.
> +  bool isFirstBitcast  = (firstOp == Instruction::BitCast);
> +  bool isSecondBitcast = (secondOp == Instruction::BitCast);
> +  bool chainedBitcast  = (SrcTy == DstTy&&  isFirstBitcast&&  isSecondBitcast);

if they are both bitcasts I don't see why you need to require SrcTy == DstTy
as well.

> +
> +  // Check if any of the bitcasts convert scalars<->vectors.
> +  if ((isFirstBitcast&&  isa<VectorType>(SrcTy) != isa<VectorType>(MidTy)) ||
> +      (isSecondBitcast&&  isa<VectorType>(MidTy) != isa<VectorType>(DstTy)))
> +    // Unless we are bitcasing to the original type, disallow optimizations.

bitcasing -> bitcasting

> +    if (!chainedBitcast) return 0;
>
>     int ElimCase = CastResults[firstOp-Instruction::CastOpsBegin]
>                               [secondOp-Instruction::CastOpsBegin];

Ciao, Duncan.