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Re: Enabling -frename-registers?
- From: Richard Biener <richard dot guenther at gmail dot com>
- To: Bernd Schmidt <bschmidt at redhat dot com>
- Cc: David Edelsohn <dje dot gcc at gmail dot com>, Jeffrey Law <law at redhat dot com>, GCC Patches <gcc-patches at gcc dot gnu dot org>, Segher Boessenkool <segher at kernel dot crashing dot org>
- Date: Wed, 4 May 2016 10:38:49 +0200
- Subject: Re: Enabling -frename-registers?
- Authentication-results: sourceware.org; auth=none
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On Wed, May 4, 2016 at 12:52 AM, Bernd Schmidt <bschmidt@redhat.com> wrote:
> On 05/03/2016 11:26 PM, David Edelsohn wrote:
>>
>> Optimizations enabled by default at -O2 should show an overall net
>> benefit -- that is the general justification that we have used in the
>> past. I request that this change be reverted until more compelling
>> evidence of benefit is presented.
>
>
> Shrug. Done. I was going to look at adding some more smarts to it to clean
> up after the register allocator; I guess I shan't bother.
>
> I must say I find the argumentation about the fallout not compelling. It's a
> normal consequence of development work, and by enabling it at -O2, we have
> found:
> * a Linux kernel bug
> * a rs6000 testsuite bug
> * some i386.md issues that can cause performance problems
> * and a compare-debug problem in regrename itself.
> All of these are _good_ things. If we don't want to run into such issues
> we'll have to cease all development work.
> I'll still submit final versions of the fixes for the i386 and compare-debug
> issues.
I agree with you here, enabling at -O2 was fine. Reverting will have
regressed PR38825 again (curiously also some SSE scheduling issue).
Thus I wonder if regrename could be integrated with sched2 itself.
Richard.
>
> Bernd