llvm dev - Feb 2015 - [LLVMdev] [RFC] AArch64: Should we disable GlobalMerge?

On 27 February 2015 at 21:26, Ahmed Bougacha <ahmed.bougacha at gmail.com>
wrote:
> Which brings us to my fallback proposal:  what about disabling the
> pass on darwin only?
That's a decision for Jim/Evan. I'm ok if they are.

> As for other targets, as a first step, making the pass run under -O3
> rather than -O1 is hopefully agreeable to everyone?
Sounds reasonable.

Even though it conflicts with LTO, that's what O3 means, as you said,
instability. People at O3 might want to fiddle with the passes
(on/off) to get the best performance for their own code/workload.

cheers,
--renato

On Fri, Feb 27, 2015 at 2:01 PM, Renato Golin <renato.golin at linaro.org>
wrote:
> On 27 February 2015 at 21:26, Ahmed Bougacha <ahmed.bougacha at
gmail.com> wrote:
>> Which brings us to my fallback proposal:  what about disabling the
>> pass on darwin only?
>
> That's a decision for Jim/Evan. I'm ok if they are.
Jim, thoughts?
>
>> As for other targets, as a first step, making the pass run under -O3
>> rather than -O1 is hopefully agreeable to everyone?
>
> Sounds reasonable.
Great!
> Even though it conflicts with LTO, that's what O3 means, as you said,
> instability. People at O3 might want to fiddle with the passes
> (on/off) to get the best performance for their own code/workload.
By the way, I'm not convinced LTO being either -O3 or -O0 is sensible.
But that's a discussion for another day =)

-Ahmed
> cheers,
> --renato

On Fri, Feb 27, 2015 at 2:15 PM, Ahmed Bougacha
<ahmed.bougacha at gmail.com> wrote:
> By the way, I'm not convinced LTO being either -O3 or -O0 is sensible.
> But that's a discussion for another day =)
Duncan tells me there is a plan to put -mno-global-merge into module
flags for this precise reason, so this would disable it for LTO as
well, when -O3 wasn't specified.  This takes care of our non-O3
concerns;  I'll have a look!

-Ahmed

> On Feb 27, 2015, at 2:15 PM, Ahmed Bougacha <ahmed.bougacha at
gmail.com> wrote:
> 
> On Fri, Feb 27, 2015 at 2:01 PM, Renato Golin <renato.golin at
linaro.org> wrote:
>> On 27 February 2015 at 21:26, Ahmed Bougacha <ahmed.bougacha at
gmail.com> wrote:
>>> Which brings us to my fallback proposal:  what about disabling the
>>> pass on darwin only?
>> 
>> That's a decision for Jim/Evan. I'm ok if they are.
> 
> Jim, thoughts?
I would prefer Darwin not differ in this regard, but I don’t feel incredibly
strongly about it. Just a general preference to keeping platform dependencies
and differences to a minimum. Whatever y’all decide is fine with me.
> 
>> 
>>> As for other targets, as a first step, making the pass run under
-O3
>>> rather than -O1 is hopefully agreeable to everyone?
>> 
>> Sounds reasonable.
> 
> Great!
> 
>> Even though it conflicts with LTO, that's what O3 means, as you
said,
>> instability. People at O3 might want to fiddle with the passes
>> (on/off) to get the best performance for their own code/workload.
> 
> By the way, I'm not convinced LTO being either -O3 or -O0 is sensible.
> But that's a discussion for another day =)
> 
> -Ahmed
> 
>> cheers,
>> --renato