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Re: match.pd: Optimize (x & y) ^ (x | y)
- From: Marc Glisse <marc dot glisse at inria dot fr>
- To: Marek Polacek <polacek at redhat dot com>
- Cc: GCC Patches <gcc-patches at gcc dot gnu dot org>, Richard Biener <rguenther at suse dot de>
- Date: Thu, 11 Jun 2015 17:25:30 +0200 (CEST)
- Subject: Re: match.pd: Optimize (x & y) ^ (x | y)
- Authentication-results: sourceware.org; auth=none
- References: <20150611110432 dot GY2756 at redhat dot com>
- Reply-to: gcc-patches at gcc dot gnu dot org
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 integers.
Note that for pure bitop (only involving &|^), testing the range [0,1] is
+/* (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 way
that makes it 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 pressure a
bit in some cases, but we have not used that as a criterion for other
simplifications in match.pd yet (LLVM does though).