Re: [RFC PATCH, i386]: Enable post-reload compare elimination pass

[Uros Bizjak <ubizjak at gmail dot com>]

On Fri, May 12, 2017 at 9:09 PM, Uros Bizjak <ubizjak@gmail.com> wrote:
> On Fri, May 12, 2017 at 8:34 PM, Jeff Law <law@redhat.com> wrote:
>> On 05/10/2017 01:05 PM, Uros Bizjak wrote:
>>>
>>> On Wed, May 10, 2017 at 5:18 PM, Uros Bizjak <ubizjak@gmail.com> wrote:
>>>>
>>>> On Wed, May 10, 2017 at 4:27 PM, Jakub Jelinek <jakub@redhat.com> wrote:
>>>>>
>>>>> On Tue, May 09, 2017 at 06:06:47PM +0200, Uros Bizjak wrote:
>>>>>>
>>>>>> Attached patch enables post-reload compare elimination pass by
>>>>>> providing expected patterns (duplicates of existing patterns with
>>>>>> setters of reg and flags switched in the parallel) for flag setting
>>>>>> arithmetic instructions.
>>>>>>
>>>>>> The merge triggers more than 3000 times during the gcc bootstrap,
>>>>>> mostly in cases where intervening memory load or store prevents
>>>>>> combine from merging the arithmetic insn and the following compare.
>>>>>>
>>>>>> Also, some recent linux x86_64 defconfig build results in ~200 merges,
>>>>>> removing ~200 test/cmp insns. Not much, but I think the results still
>>>>>> warrant the pass to be enabled.
>>>>>
>>>>>
>>>>> Isn't the right fix instead to change the compare-elim.c pass to either
>>>>> accept both reg vs. flags orderings in parallel, or both depending
>>>>> on some target hook, or change it to the order i386.md and most other
>>>>> major targets use and just fix up mn10300/rx (and aarch64?) to use the
>>>>> same
>>>>> order?
>>>
>>>
>>> Attached patch changes compare-elim.c order to what i386.md expects.
>>>
>>> Thoughts?
>>
>> I think with an appropriate change to the canonicalization rules in the
>> manual this is fine.
>>
>> I've got the visium, rx and mn103 patches handy to ensure they don't
>> regress.  aarch64 doesn't seem to be affected either way but I didn't
>> investigate why -- I expected it to improve with your change.
>>
>> I'll write up a ChangeLog and commit the mn103, rx and visium changes after
>> you commit the compare-elim & documentation bits.

Something like the attached patch?

2017-05-12  Uros Bizjak  <ubizjak@gmail.com>

    * doc/md.texi ( Canonicalization of Instructions): Describe the
    canonical form of instructions that inherently set a condition
    code register.

Uros.

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