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Re: match.pd: Optimize (x & y) ^ (x | y)
- From: Richard Biener <rguenther at suse dot de>
- To: gcc-patches at gcc dot gnu dot org,Marc Glisse <marc dot glisse at inria dot fr>,Marek Polacek <polacek at redhat dot com>
- Date: Thu, 11 Jun 2015 18:04:01 +0200
- Subject: Re: match.pd: Optimize (x & y) ^ (x | y)
- Authentication-results: sourceware.org; auth=none
- References: <20150611110432 dot GY2756 at redhat dot com> <alpine dot DEB dot 2 dot 20 dot 1506111717100 dot 8389 at stedding dot saclay dot inria dot fr>
On June 11, 2015 5:25:30 PM GMT+02:00, Marc Glisse <email@example.com> wrote:
>On Thu, 11 Jun 2015, Marek Polacek wrote:
>> I have verified this transformation on a toy testcase (tried x and y
>> in the range [-1000,1000]) and it does a correct thing for all
>Note that for pure bitop (only involving &|^), testing the range [0,1]
>> +/* (x & y) ^ (x | y) -> x ^ y */
>> + (bit_xor:c (bit_and@2 @0 @1) (bit_ior@3 @0 @1))
>Make either bit_and or bit_ior commutative? Or do we canonicalize in a
>that makes it unnecessary?
Yes, operand canonicalization should make this unnecessary.
>> + (if (single_use (@2) && single_use (@3))
>> + (bit_xor @0 @1)))
>I don't think we should use single_use here. The result is never more
>complicated than the original. Sure, it might increase register
>bit in some cases, but we have not used that as a criterion for other
>simplifications in match.pd yet (LLVM does though).
Hmm yes, you are right here.