[llvm-commits] Slot alignment

[Mon P Wang]

Hi Bill,

I'll make those changes.

Thanks,
   -- Mon Ping

On Jul 1, 2008, at 9:07 PM, Bill Wendling wrote:

> On Jul 1, 2008, at 6:38 PM, Mon P Wang wrote:
>
>> Hi,
>>
>> The following small patch is to fix a problem when we have to
>> EmitStackConvert.  It is possible that two types of the same size
>> may have different alignment (e.g., users may specify a stricter
>> alignment than native or vector types may have stricter alignment
>> than a scalar of the same size).  If one ever tries to do stack
>> convert of this, we create a stack slot with the alignment of the
>> destination and we can generate a load/store with greater alignment
>> than the stack slot that we have created.  The following patch
>> generates a StackSlot with the minimum alignment necessary for both
>> the source and the destination type.  If you have any comments,
>> please let me know.
>>
> Hi Mon Ping,
>
> A couple of comments.
>
> Index: include/llvm/CodeGen/SelectionDAG.h
> ===================================================================
> --- include/llvm/CodeGen/SelectionDAG.h	(revision 52999)
> +++ include/llvm/CodeGen/SelectionDAG.h	(working copy)
> @@ -574,9 +574,11 @@
>    void dump() const;
>
>    /// CreateStackTemporary - Create a stack temporary, suitable for
> holding the
> -  /// specified value type.
> +  /// specified value type.  If minAlign is specified, the slot size
> will have
> +  /// at least that alignment.
>    SDOperand CreateStackTemporary(MVT VT);
> -
> +  SDOperand CreateStackTemporary(MVT VT, unsigned minAlign);
> +
>    /// FoldSetCC - Constant fold a setcc to true or false.
>    SDOperand FoldSetCC(MVT VT, SDOperand N1,
>                        SDOperand N2, ISD::CondCode Cond);
> Index: lib/CodeGen/SelectionDAG/SelectionDAG.cpp
> ===================================================================
> --- lib/CodeGen/SelectionDAG/SelectionDAG.cpp	(revision 52999)
> +++ lib/CodeGen/SelectionDAG/SelectionDAG.cpp	(working copy)
> @@ -1081,15 +1081,20 @@
>  /// CreateStackTemporary - Create a stack temporary, suitable for
> holding the
>  /// specified value type.
>  SDOperand SelectionDAG::CreateStackTemporary(MVT VT) {
> +  return CreateStackTemporary(VT, 1);
> +}
> +
> +SDOperand SelectionDAG::CreateStackTemporary(MVT VT, unsigned
> minAlign) {
>
> It's not necessary to create two functions. Just specify a default
> value for minAlign like so:
>
> +  SDOperand CreateStackTemporary(MVT VT, unsigned minAlign = 1);
>
>
> +  if (StackAlign < minAlign)
> +    StackAlign = minAlign;
>
> You could use std::max here.
>
>
>
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