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[Bug tree-optimization/23181] [4.1 Regression] Dominator opts slows down bresenham line drawing by roughly 20%
- From: "hubicka at ucw dot cz" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 1 Aug 2005 15:14:13 -0000
- Subject: [Bug tree-optimization/23181] [4.1 Regression] Dominator opts slows down bresenham line drawing by roughly 20%
- References: <20050801143216.23181.hubicka@gcc.gnu.org>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Additional Comments From hubicka at ucw dot cz 2005-08-01 15:14 -------
Subject: Re: [4.1 Regression] Dominator opts slows down bresenham line drawing by roughly 20%
One problem is that DOM manages to convert
a += 1;
if (....)
a += 10;
to
a1 = a + 1
if (....)
a1 = a + 11
a1 = a
hence the extra move even on 3-address architectures. There are two
such additions done in parallel so we won't get cmove.
We either need to go the all way around and produce if-then-else and
save one instruction or avoid this transformation as it is dificult to
undo.
Honza
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23181