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Re: [PATCH, PR target/65103, 2/3] Propagate address constants into loops for i386
- From: Ilya Enkovich <enkovich dot gnu at gmail dot com>
- To: Jeff Law <law at redhat dot com>
- Cc: gcc-patches <gcc-patches at gcc dot gnu dot org>, rdsandiford at googlemail dot com
- Date: Thu, 25 Jun 2015 17:01:46 +0300
- Subject: Re: [PATCH, PR target/65103, 2/3] Propagate address constants into loops for i386
- Authentication-results: sourceware.org; auth=none
- References: <20150310150027 dot GC27860 at msticlxl57 dot ims dot intel dot com> <8761a22ecm dot fsf at googlemail dot com> <552CA415 dot 5060206 at redhat dot com> <CAMbmDYZ=Yd7vZ8tPZw36iCVtk5C7kzAiTdi8QuoWs627touB0g at mail dot gmail dot com> <20150417083445 dot GA6178 at msticlxl57 dot ims dot intel dot com> <5535E5B1 dot 9020309 at redhat dot com> <CAMbmDYbcLiU5QcQ053RF9PofPZWxjdrfDTNWffpWZvnV9pzAOA at mail dot gmail dot com> <5567939F dot 9060507 at redhat dot com> <CAMbmDYZerRFMiTpo3Am8LyPN504uga+wjt+ow=NyKWVK0qNzuw at mail dot gmail dot com>
Ping
2015-06-01 15:26 GMT+03:00 Ilya Enkovich <enkovich.gnu@gmail.com>:
> 2015-05-29 1:15 GMT+03:00 Jeff Law <law@redhat.com>:
>>
>> Right, but you're blindly propagating. The right thing to do is look at
>> some kind of metric to estimate when it's profitable to propagate the
>> constant back in vs leave it hoisted out.
>
> No, the patch is not to blindly propagate but to let loop invariant to
> be propagated into address. Existing propagation gain estimation
> (should_replace_address) still applies.
>
> Thanks,
> Ilya
>
>>
>> If you look at what Kugan is doing in cprop.c, that's exactly the approach
>> he's taking -- looking at rtx costing to determine when to propagate the
>> constant back into the loop. It could probably be made better with some
>> knowledge of register pressure and looking at whether or not all uses (vs
>> just some uses) of the constant will be propagated.
>>
>> Jeff