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Re: IRA costs tweaks, PR 56069
- From: Richard Sandiford <rdsandiford at googlemail dot com>
- To: Bernd Schmidt <bschmidt at redhat dot com>
- Cc: Vladimir Makarov <vmakarov at redhat dot com>, GCC Patches <gcc-patches at gcc dot gnu dot org>
- Date: Mon, 07 Mar 2016 20:29:19 +0000
- Subject: Re: IRA costs tweaks, PR 56069
- Authentication-results: sourceware.org; auth=none
- References: <56D71977 dot 5040204 at t-online dot de> <56D72316 dot 2060207 at redhat dot com> <56D760CF dot 4030308 at redhat dot com> <56D87852 dot 6000207 at redhat dot com>
Bernd Schmidt <bschmidt@redhat.com> writes:
> On 03/02/2016 10:53 PM, Vladimir Makarov wrote:
>>> 2. update_costs_from_allocno records a cost update not just for the
>>> initial allocno, but for each of the visited ones. I can sort of see
>>> an argument for doing that (let's say if you assign an allocno in the
>>> middle of a copy chain you'd want the tail end of the chain to be
>>> reset), but in practice I don't think the present algorithm can work
>>> at all. In the case of an allocno in the middle of a copy chain the
>>> restore would progress in both directions, and in any case it looks
>>> like this approach can end up double-counting things when restoring
>>> costs.
>>>
>> It is just a heuristic. Richard Sandiford proposed this update
>> approach. Before it we had only updates of allocnos directly connected
>> to allocno in question. Richard's approach helped to improve code in
>> some cases. If something works better we should use. The bechmarking
>> is the best criterium.
>
> Ccing Richard in case he has comments.
TBH I don't remember anything about this now. Is it:
https://gcc.gnu.org/ml/gcc-patches/2008-09/msg00541.html
? I think that was just tweaking the traversal order in an existing
cost update, rather than adding a new one.
You might be talking about a different patch though, sorry.
Richard