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Re: [PATCH 2/4] match.pd: Add x & ~(x & y) -> x & ~y pattern
- From: Marc Glisse <marc dot glisse at inria dot fr>
- To: gcc-patches at gcc dot gnu dot org
- Cc: rv at rasmusvillemoes dot dk
- Date: Wed, 21 Jan 2015 21:00:45 +0100 (CET)
- Subject: Re: [PATCH 2/4] match.pd: Add x & ~(x & y) -> x & ~y pattern
- Authentication-results: sourceware.org; auth=none
Hello,
(sorry for the broken thread, for some reason I haven't received any email
from gcc since about 10am, I'll investigate later)
+/* x & ~(x & y) -> x & ~y */
+(simplify
+ (bit_and:c @0 (bit_not (bit_and:c@2 @0 @1)))
+ (if (TREE_CODE (@2) != SSA_NAME || has_single_use (@2))
+ (bit_and @0 (bit_not @1))))
Wouldn't it make more sense to put @2 on bit_not? If bit_and is used
multiple times, the transformation is neutral so it should be done as a
canonicalization. On the other hand, if bit_not is used multiple times,
the transformation adds an extra bit_not (which might be free when there
is an andn insn). So I believe the 2 main options are:
- move @2 on the bit_not
- don't test has_single_use at all
--
Marc Glisse