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[Bug tree-optimization/42108] [4.4/4.5 Regression] 50% performance regression
- From: "matz at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 14 Dec 2009 04:55:27 -0000
- Subject: [Bug tree-optimization/42108] [4.4/4.5 Regression] 50% performance regression
- References: <bug-42108-9410@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #26 from matz at gcc dot gnu dot org 2009-12-14 04:55 -------
And if I fix this problem (so that only one reference to *n_9) remains
I hit the problem that the fortran frontend emits the computation of countm1
after the loop bound test. No pass is moving code in front of that test as
this is potentially a regression (more evaluations in out-of-bound case).
And if I fix _that_ I hit the problem of the fix for PR38819. PRE won't move
the division at all, because it could trap :-/ If I disable this I get back
the 4.3 performance.
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42108