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

On February 4, 2015 9:35:13 AM CET, Jakub Jelinek <> 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
>> 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
>> 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
>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.


>> Regstrapped on x86_64-linux-gnu and i686-pc-linux-gnu.  Ok to
>> for  gcc/ChangeLog
>> 	* simplify-rtx.c (simplify_binary_operation_1): Simplify one
>> 	of two XORs that have an intervening AND or IOR.
>Ok, thanks.
>	Jakub

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