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[Bug fortran/41137] inefficient zeroing of an array
- From: "burnus at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 21 Jun 2010 15:02:06 -0000
- Subject: [Bug fortran/41137] inefficient zeroing of an array
- References: <bug-41137-6642@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #7 from burnus at gcc dot gnu dot org 2010-06-21 15:02 -------
(In reply to comment #1)
> Just for reference, the difference in time between the two variants is truly
> impressive. About a factor of 11 with gcc 4.4 and 8 with gcc 4.5.
I get for the example the following values, note especially the newly added
CONTIGUOUS result:
0.31601900 - assumed-shape
0.21601403 - assumed-shape CONTIGUOUS
0.21601295 - explicit size (n,n,...)
0.20801300 - explicit size (10,10,...)
0.21601403 - explicit size (10*10*...)
Ignoring some measuring noise, assumed-shape is 46% (-O0) to 25% (-O3) slower
than explicit size, but using the CONTIGUOUS attribute, the performance is
re-gained. I cannot reproduce the factor of 10 results, however. What surprises
me a bit is that -flto -fwhole-program does not reduce the speed penalty of
assumed-shape arrays.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41137