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Re: [PATCH] Move X - (X / Y) * Y folding to match.pd

From: Marc Glisse <marc dot glisse at inria dot fr>
To: Marek Polacek <polacek at redhat dot com>
Cc: Richard Biener <rguenther at suse dot de>, GCC Patches <gcc-patches at gcc dot gnu dot org>
Date: Tue, 30 Jun 2015 00:22:35 +0200 (CEST)
Subject: Re: [PATCH] Move X - (X / Y) * Y folding to match.pd
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References: <20150626162940 dot GI10139 at redhat dot com> <alpine dot DEB dot 2 dot 20 dot 1506271524590 dot 1949 at laptop-mg dot saclay dot inria dot fr> <alpine dot LSU dot 2 dot 11 dot 1506290931290 dot 26650 at zhemvz dot fhfr dot qr> <20150629140133 dot GM10139 at redhat dot com>
Reply-to: gcc-patches at gcc dot gnu dot org

On Mon, 29 Jun 2015, Marek Polacek wrote:

On Mon, Jun 29, 2015 at 09:36:59AM +0200, Richard Biener wrote:

Anything wrong with this?

+/* X - (X / Y) * Y is the same as X % Y.  */
+(simplify
+ (minus (convert? @0) (convert? (mult (trunc_div @0 @1) @1)))
+ (if (INTEGRAL_TYPE_P (type) || VECTOR_INTEGER_TYPE_P (type))
+  (convert (trunc_mod @0 @1))))


That looks awfully similar to a variant I also tried (but I remember
having convert1? and convert2? in it).  Not sure what was wrong with
that one; certainly yours seems to work fine.

Afterwards I thought of a limitation. Nothing bad, but it highlights atrap I regularly fall into: several @0 in the same pattern may havedifferent types (for INTEGER_CST, operand_equal_p mostly ignores thetype). So for an int x, 42L-42/x*x should fail to match, while usingconvert1? and convert2? should match.


--
Marc Glisse

Follow-Ups:
- Re: [PATCH] Move X - (X / Y) * Y folding to match.pd
  - From: Richard Biener

References:
- [PATCH] Move X - (X / Y) * Y folding to match.pd
  - From: Marek Polacek
- Re: [PATCH] Move X - (X / Y) * Y folding to match.pd
  - From: Marc Glisse
- Re: [PATCH] Move X - (X / Y) * Y folding to match.pd
  - From: Richard Biener
- Re: [PATCH] Move X - (X / Y) * Y folding to match.pd
  - From: Marek Polacek

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