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Re: [PR48866] three alternative fixes
- From: Alexandre Oliva <aoliva at redhat dot com>
- To: Michael Matz <matz at suse dot de>
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Wed, 01 Jun 2011 19:28:15 -0300
- Subject: Re: [PR48866] three alternative fixes
- References: <ory61o1lpf.fsf@livre.localdomain> <orlixo1iih.fsf@livre.localdomain> <Pine.LNX.4.64.1105301524060.9668@wotan.suse.de>
On May 30, 2011, Michael Matz <matz@suse.de> wrote:
> Hi,
> On Mon, 30 May 2011, Alexandre Oliva wrote:
>> > 3. expand dominators before dominated blocks, so that DEFs of
>> > replaceable SSA names are expanded before their uses. Expand them
>> > when they're encountered, but not requiring a REG as a result.
>> > Save the RTL expression that results from the expansion for use in
>> > debug insns and at the non-debug use.
>>
>> This patch addresses some of the problems in 2, avoiding expanding code
>> out of order within a block, and (hopefully) ensuring that, expanding
>> dominators before dominatedblocks, DEFs are expanded before USEs.
> That isn't necessary. Replaceable SSA_NAMEs are defined in the same BB as
> their use, and hence they're expanded strictly before their use already
> right now.
Hmm... You're obviously right. I must have misinterpreted some other
failure, then. Thanks, this enables some simplification to two of the
patches.
>> There is a theoretical possibility that a USE may be expanded before a
>> DEF, depending on internal details of out-of-ssa,
> This can only happen with non-replaceable SSA_NAMEs and I thought you wish
> to deal only with replaceable.
Yup.
> That said, I dislike approach 2 for the same worries you noted. And with
> the above I don't see why your approach (3) isn't workable without changes
> to the BB order, which should then be a really small patch.
Yup. I'll give that a try.
> As SSA_NAMEs are (fairly) dense it might be better to simply use an
> array instead of a pointer_map for the SSA_NAME->rtx mapping.
Likewise.
Thanks!
--
Alexandre Oliva, freedom fighter http://FSFLA.org/~lxoliva/
You must be the change you wish to see in the world. -- Gandhi
Be Free! -- http://FSFLA.org/ FSF Latin America board member
Free Software Evangelist Red Hat Brazil Compiler Engineer