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i686 double alignment vs performance
- To: egcs at cygnus dot com, g77-alpha at gnu dot org
- Subject: i686 double alignment vs performance
- From: tprince at cat dot e-mail dot com
- Date: Wed, 08 Jul 1998 13:52:58 EDT
I got the following geometric mean Mflops from Livermore
Kernels lfk537e.f (double precision), with my modifications. Both
g77 and egcs are compiled with binutils-2.9.1 installed, with
-O2 -malign-double -march=pentiumpro -funroll-lloops so that I
believe the loop code alignments are reasonable and
comparable.
Compiler PPro/200 P II/233
g77-0.5.23 14.8 50
egcs-0628 35.8 50
lf90-4.50d 42.5 55
So, the additional alignments currently generated in egcs must
give it a tremendous advantage on the pentiumpro, but the
pentium2 isn't so dependent on them. If I compare egcs and
g77 without -funroll-loops, however, egcs often has an
advantage even on P II. If I turn off -malign-double, performance
drops significantly in every case, but more so with egcs on PPro.
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