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Re: [Patch ifcvt costs 0/3] Introduce a new target hook for ifcvt costs.
- From: Jeff Law <law at redhat dot com>
- To: Bernd Schmidt <bschmidt at redhat dot com>, James Greenhalgh <james dot greenhalgh at arm dot com>, Richard Biener <richard dot guenther at gmail dot com>
- Cc: GCC Patches <gcc-patches at gcc dot gnu dot org>, Ramana Radhakrishnan <Ramana dot Radhakrishnan at arm dot com>, Bernd Schmidt <bernds_cb1 at t-online dot de>, Eric Botcazou <ebotcazou at libertysurf dot fr>, Steven Bosscher <steven at gcc dot gnu dot org>
- Date: Fri, 9 Oct 2015 09:28:46 -0600
- Subject: Re: [Patch ifcvt costs 0/3] Introduce a new target hook for ifcvt costs.
- Authentication-results: sourceware.org; auth=none
- References: <20150911095608 dot GA2448 at arm dot com> <1443193479-10830-1-git-send-email-james dot greenhalgh at arm dot com> <CAFiYyc3hXgTiE3q9pBz_57GzUYJH3=8J8tmb0Hg1tGL=zpwtQg at mail dot gmail dot com> <20150929143128 dot GA15969 at arm dot com> <560CFEE1 dot 4050300 at redhat dot com> <5617A4DE dot 6020004 at redhat dot com>
On 10/09/2015 05:28 AM, Bernd Schmidt wrote:
I don't know whether you've done any more work on the patch series, but
I think I've made up my mind that optimizing the sequence before
computing its cost would be a good thing to try first. Either with a
better expander interface which generates the right thing immediately,
or running something like cselib over the generated code. I think this
would give more reliable results rather than guesstimating a redundancy
factor in the cost function.
Another great example of what we could do if we could give an RTL
sequence and mini CFG to the various optimizers and have them just work
on the sequence (making the appropriate assumptions about live-in and
live-out objects). Retrofitting this capability would likely be very
hard at this point :(
Even just DCE & CSE would probably be a notable step forward.
jeff