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Re: [PR64817-related 3/3] simplify xor of (and or ior) of xor


On February 4, 2015 10:15:30 AM CET, Jakub Jelinek <jakub@redhat.com> wrote:
>On Wed, Feb 04, 2015 at 09:54:53AM +0100, Richard Biener wrote:
>> On February 4, 2015 9:35:13 AM CET, Jakub Jelinek <jakub@redhat.com>
>wrote:
>> >On Wed, Feb 04, 2015 at 04:21:43AM -0200, Alexandre Oliva wrote:
>> >> I'm a bit surprised the gimple layer does not even attempt to
>> >simplify
>> >> them, but I didn't try to tackle that, since I was not even sure
>this
>> >> was a useful optimization.  After all, how often do we see xor of
>and
>> >of
>> >> xor of and of xor of... in the wild, rather than in pathological
>> >> testcases? :-)  But hey, at least the rtl simplification is cheap,
>so
>> >> why not?
>> >
>> >I think we should teach at least VRP to simplify debug stmts
>similarly
>> >how
>> >it simplifies normal comparisons etc. using value ranges, but that
>> >would be
>> >stage1 material.
>> 
>> So I suppose this is only about debug exprs and we optimize regular
>gimple
>> well?  Otherwise adding some patterns to match.PD could help.
>
>Sure.  For e.g. VRP I meant that simplify_stmt_using_ranges could also
>attempt to simplify (some) debug_bind stmts, similarly how it optimizes
>normal stmts.

Sure.  Of course it's bad that debug stmts use Generic...  General fold-stmt could do some of the work.  Also that debug temps have no use-def chains doesn't help too much.

Richard.

>	Jakub



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