[PATCH] [AArch64] Enable partial unrolling and runtime unrolling for AArch64 target

[Eric Christopher]

On Tue, Sep 9, 2014 at 12:19 PM, Bob Wilson <bob.wilson at apple.com> wrote:

>
> On Sep 9, 2014, at 11:40 AM, Eric Christopher <echristo at gmail.com> wrote:
>
>
>
> On Tue, Sep 9, 2014 at 8:57 AM, Hal Finkel <hfinkel at anl.gov> wrote:
>
>> ----- Original Message -----
>> > From: "Renato Golin" <renato.golin at linaro.org>
>> > To: "Tilmann Scheller" <t.scheller at samsung.com>
>> > Cc: reviews+D5148+public+3607c133967fc2d2 at reviews.llvm.org, "LLVM
>> Commits" <llvm-commits at cs.uiuc.edu>
>> > Sent: Tuesday, September 9, 2014 9:33:39 AM
>> > Subject: Re: [PATCH] [AArch64] Enable partial unrolling and runtime
>> unrolling for AArch64 target
>> >
>> > On 9 September 2014 15:15, Tilmann Scheller <t.scheller at samsung.com>
>> > wrote:
>> > > can we make sure this is enabled only with -O3 rather than -O2/-Os
>> > > though?
>> > > (at least until the code size regressions are fixed)
>> >
>> > Good point!
>>
>> In case this helps: The way this works is that functions compiled with
>> -Os get the 'optsize' attribute added. The UnrollingPreferences structure
>> has both an PartialThreshold and an PartialOptSizeThreshold parameter that
>> can be set accordingly.
>>
>
> Right, 50% is still a pretty large code size increase even for O2, so O3
> might be best here.
>
>
> I will go one step further.
>
> 50% code size regression, even on just a few tests, is completely
> unacceptable for -O2.
>
> For -O3, it might be tolerable if it provides a very significant
> performance win to compensate. It doesn’t sound like the performance is
> really that compelling, though. I think this should be under the control of
> a separate option, not enabled by default for -O3, until the code size
> regressions get fixed.
>
>
This sounds good to me too.

-eric

>
> Kevin: Are you going to work on the code size issues or...?
>
>
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