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g77/x86 unroll-loops performance
- To: egcs at egcs dot cygnus dot com (IPM Return requested) (Receipt notification requested) (Reply requested)
- Subject: g77/x86 unroll-loops performance
- From: Tim C Prince <Prince_Tim_C at solarturbines dot com>
- Date: 03 May 1999 16:00:00 Z
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The performance of -O2 has improved significantly in recent
snapshots, emphasizing some of the cases where the compiler
stumbles over unrolling at -O2. Is there an adjustable switch
which would reduce the tendency to unroll when good
performance is obtained without unrolling? Kernel 18 is really
more extreme than it appears, as big gains from unrolling one
part are offset by big losses in the other parts. Pentium II shows
similar comparisons, except that it saturates L1 cache
performance in several kernel tests.
*********************************************
THE LIVERMORE FORTRAN KERNELS "MFLOPS" TEST:
*********************************************
Run on Pentium Pro 200 Mhz
Compiled on egcs-19990502/g77 -O2 -malign-double
-march=pentiumpro
-funroll-loops not unrolled
KERNEL MFLOP/SEC
------ ---------
1 86.081 82.372
2 83.863 77.847
3 104.491 93.196
4 132.464 94.817
5 47.104 46.898
6 78.903 61.202
7 74.986 94.291
8 74.830 79.672
9 71.458 87.320
10 18.145 22.260
11 59.176 61.011
12 71.013 62.006
13 6.022 6.012
14 15.843 17.106
15 20.360 20.658
16 34.316 34.711
17 44.569 40.450
18 58.901 60.349
19 48.101 47.506
20 25.388 27.017
21 107.685 85.799
22 9.608 9.631
23 99.967 100.153
24 20.315 21.297
Dr. Timothy C. Prince
Consulting Engineer
Solar Turbines, a Caterpillar Company
alternate e-mail: tprince@computer.org