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Re: GCC47 movmem breaks RA, GCC46 RA is fine
On Fri, Apr 27, 2012 at 12:00 PM, Paulo J. Matos <paulo@matos-sorge.com> wrote:
> On 27/04/12 09:21, Richard Guenther wrote:
>>>
>>>
>>> This differs from what GCC47 does and seems to work better.
>>> I would like help on how to best handle this situation under GCC47.
>>
>>
>> Not provide movmem which looks like open-coded and not in any way
>> "optimized"?
>>
>
> Thanks Richard, however I don't understand your comment.
> GCC46 outputs for this problem:
> $t25:
> ? ? ? ?enterl ?#H'0002
> ? ? ? ?st ? ? ?AL,@H'fff9
> ? ? ? ?st ? ? ?AH,@H'fff8
> ? ? ? ?ld ? ? ?X,@$XAP_AH
> ? ? ? ?ld ? ? ?X,@(0,X)
> ? ? ? ?ld ? ? ?AL,#H'0010
> ? ? ? ?ld ? ? ?AH,@H'fff9
> ? ? ? ?bc2
> ? ? ? ?ld ? ? ?AL,@H'fff8
> ? ? ? ?leavel ?#H'0002
>
> and GCC47, once movmemqi and setmemqi are disabled:
> $t25:
> ? ? ? ?enterl ?#H'0005
> ? ? ? ?st ? ? ?AH,@(H'0001,Y)
> ? ? ? ?ld ? ? ?X,@$XAP_AH
> ? ? ? ?ld ? ? ?X,@(0,X)
> ? ? ? ?ld ? ? ?AH,#H'0010
> ? ? ? ?st ? ? ?AH,@(0,Y)
> ? ? ? ?ld ? ? ?AH,@$XAP_UXL
> ? ? ? ?bsr ? ? $memcpy
> ? ? ? ?ld ? ? ?AL,@(H'0001,Y)
> ? ? ? ?leavel ?#H'0005
>
>
> It feels to me that GCC46 version is better:
> * no branch to subroutine memcpy;
> * less stack usage (argument to enterl);
>
> So, using our block copy (bc2) instruction is an optimisation, don't you
> think?
Yes, it inlines it. You may want to look at s390 which I believe has
a similar block-copy operation.
Richard.
> --
> PMatos
>