Re: egcs 1.0.1 and fortran optimization

[Vladimir Eltsov <ve at boojum dot hut dot fi>]

Thank you for all who replied to my question why egcs f77 compiler
produces slower code on pentiumII than gf77 2.7.2.3.f.1 when c++ compiler
produces much faster code with the same set of compiler options. The most 
imperative answer was to always use -malign-double for double precision
fortran programs. So I want to post my experience which contradicts this
conclusion. After playing with various optimization options I found the
best result for one paticular fortran program which solves system of
ODE's using the standard rksuit package (from www.netlib.org). The best
options for egcs are
-O9 -mcpu=pentiumpro -fomit-frame-pointer -ffast-math 
 -funroll-loops -fforce-mem
while for gnu f77 
-O3 -m486 -fomit-frame-pointer -ffast-math -malign-double -funroll-loops

With these options egcs compiled program runs 2.5% faster than gf77
compiled. However, adding -malign-double to egcs options slows down the
resulting program by 17% (-fno-automatic and -fforce-addr also have
negative effects, others mentioned in the g77 manual have no effect). All
real variables in the program are DP and all common blocks are arranged
form longest to shortest.

Best regards,

   Vladimir Eltsov