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Re: [patch] Excessive alignment in ix86_data_alignment


On Thu, Oct 9, 2014 at 1:37 AM, Uros Bizjak <ubizjak@gmail.com> wrote:
> On Thu, Oct 9, 2014 at 10:25 AM, Kirill Yukhin <kirill.yukhin@gmail.com> wrote:
>> On 08 Oct 23:02, Petr Murzin wrote:
>>> Hi,
>>> I have measured performance impact on Haswell platform according to this
>>> input:
>>> https://gcc.gnu.org/ml/gcc-patches/2014-06/msg00978.html

Kirill, please mention:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61296

in your ChangeLog.

> What about older processors?

Kirill, please collect data on Nehelam/Westmere, Sandybrigde/Ivybride
and Silvermont.

> The optimization was introduced well before Haswell for then current
> processors, and it was based on the recommendation from Intel
> optimization guide. If this optimization doesn't apply for new
> processors, then tune option should be introduced and set accordingly.
>

I believe the original excessive alignment was introduced by cut/paste
from

https://gcc.gnu.org/git/?p=gcc.git;a=patch;h=ed45e834f305d1f2709bf200a13d5beebc2fcfee

to improve x86 FP performance, which might be partially copied from
CONSTANT_ALIGNMENT:

https://gcc.gnu.org/git/?p=gcc.git;a=patch;h=f7d6703c5d83fc9fb06246d6eb49e9b61098045c


-- 
H.J.


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