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[Bug target/38306] [4.4 Regression] 15% slowdown of computational kernel
- From: "rguenth at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 30 Nov 2008 11:38:53 -0000
- Subject: [Bug target/38306] [4.4 Regression] 15% slowdown of computational kernel
- References: <bug-38306-6642@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #2 from rguenth at gcc dot gnu dot org 2008-11-30 11:38 -------
Due to the high density of branches in the code this is easily a code layout
and/or padding issue. Different architectures have different constraints on
their decoders and branch predictors related to branch density. Core
introduces other branch limitations for loops that engage the loop stream
detector.
We do not at all try to properly optimize (or even model) this apart
from inserting nops. YMMV with -fschedule-insns.
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38306