[llvm-commits] [llvm] r173620 - Legalizer: Add an assert and tweak a comment to clarify the assumptions this code makes.

[Duncan Sands]

Hi Benjamin,

On 27/01/13 16:04, Benjamin Kramer wrote:
> Author: d0k
> Date: Sun Jan 27 09:04:43 2013
> New Revision: 173620
>
> URL: http://llvm.org/viewvc/llvm-project?rev=173620&view=rev
> Log:
> Legalizer: Add an assert and tweak a comment to clarify the assumptions this code makes.
>
> Modified:
>      llvm/trunk/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
>
> Modified: llvm/trunk/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp?rev=173620&r1=173619&r2=173620&view=diff
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp (original)
> +++ llvm/trunk/lib/CodeGen/SelectionDAG/LegalizeIntegerTypes.cpp Sun Jan 27 09:04:43 2013
> @@ -2098,9 +2098,13 @@ void DAGTypeLegalizer::ExpandIntRes_Shif
>       EVT VT = LHSL.getValueType();
>
>       // If the shift amount operand is coming from a vector legalization it may
> -    // not have the right return type.  Fix that first by casting the operand.
> +    // have an illegal type.  Fix that first by casting the operand.  Otherwise
> +    // the new SHL_PARTS operation would need further legalization, and the
> +    // legalizer assumes that illegal SHL_PARTS never occur.

this seems like a strange formulation to me.  The legalizer could easily be
taught to handle an illegal shift amount.  Isn't it more that it's simpler and
more efficient to simply not create such shl_parts in the first place?

Ciao, Duncan.

>       SDValue ShiftOp = N->getOperand(1);
>       MVT ShiftTy = TLI.getShiftAmountTy(VT);
> +    assert(ShiftTy.getSizeInBits() >= Log2_32_Ceil(VT.getSizeInBits()) &&
> +           "ShiftAmountTy is too small to cover the range of this type!");
>       if (ShiftOp.getValueType() != ShiftTy)
>         ShiftOp = DAG.getZExtOrTrunc(ShiftOp, dl, ShiftTy);
>
>
>
> _______________________________________________
> llvm-commits mailing list
> llvm-commits at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>