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Re: update address taken: don't drop clobbers
- From: Michael Matz <matz at suse dot de>
- To: Richard Biener <richard dot guenther at gmail dot com>
- Cc: Marc Glisse <marc dot glisse at inria dot fr>, GCC Patches <gcc-patches at gcc dot gnu dot org>
- Date: Thu, 10 Jul 2014 17:48:56 +0200 (CEST)
- Subject: Re: update address taken: don't drop clobbers
- Authentication-results: sourceware.org; auth=none
- References: <alpine dot DEB dot 2 dot 02 dot 1406282350110 dot 31815 at stedding dot saclay dot inria dot fr> <CAFiYyc0fRhV09A3C2WT8yQ1ndp9dcyWntCVSPHzhwHb3tgNZLg at mail dot gmail dot com>
On Thu, 10 Jul 2014, Richard Biener wrote:
> Apart from the out-of-SSA patch you proposed elsewhere a possibility
> is to simply never mark undefined SSA names as
> SSA_NAME_OCCURS_IN_ABNORMAL_PHI ... (or not mark those
> as must-coalesce).
The insight to note is, that undefined SSA names should really be
coalesced with something (otherwise you lost an optimization opportunity),
but it doesn't matter with _what_ each use of the undefined name is
coalesced, you can even identify different uses of them with different SSA
names (e.g. the LHS of each using stmt). Requires some change in the
order things are done in out-of-ssa.