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[Bug target/27855] reassociation pass produces ~30% slower matrix multiplication code
- From: "pinskia at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 3 Jun 2006 02:49:58 -0000
- Subject: [Bug target/27855] reassociation pass produces ~30% slower matrix multiplication code
- References: <bug-27855-1649@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #7 from pinskia at gcc dot gnu dot org 2006-06-03 02:49 -------
If you change the code to be integers, this also cause the drop too with
reassociation even without -ffast-math so it is unrelated to the fact
-ffast-math turns on reassociate for floating points for fast math.
So what is happening is that the add to rC[0-4]_0 is being further down which
causes variable's life to be extended. Yes there should be a pass at the tree
level which optimizes variable's life time but I don't know how much use that
is without a better register allocator in the first place.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27855