Sean Chittenden <sean@chittenden.org> writes:
> Is there a place where -fno-fast-math
> could be used as a CC option if the CC is gcc?
configure is what I had in mind ;-). I can't think of any part of the
code where we'd really want this sort of optimization enabled.
> After looking through gcc, using -O and -ffast-math will create broken
> code, but -O2 -ffast-math _should_ be okay.
At least in the gcc shipped with Red Hat 7.2, it doesn't seem to matter:
you get the wrong answer regardless of -O level. Here's the test case
I used:
[tgl@rh1 tgl]$ cat bug.c
#include <stdio.h>
double d18000 = 18000.0;
main() {
int d = d18000 / 3600;
printf("18000.0 / 3600 = %d\n", d);
return 0;
}
[tgl@rh1 tgl]$ gcc bug.c
[tgl@rh1 tgl]$ ./a.out
18000.0 / 3600 = 5 -- right
[tgl@rh1 tgl]$ gcc -O2 -ffast-math bug.c
[tgl@rh1 tgl]$ ./a.out
18000.0 / 3600 = 4 -- wrong
-- I get 4 if -ffast-math, -O doesn't affect it
[tgl@rh1 tgl]$ gcc -v
Reading specs from /usr/lib/gcc-lib/i386-redhat-linux/2.96/specs
gcc version 2.96 20000731 (Red Hat Linux 7.1 2.96-98)
regards, tom lane
