Thanks for pointing out various options, Andrew.
The behavior of a numerical code I'm working on varies
drastically depending on whether I've compiled it with
the -g or -O flags.
The code's behavior under -g is much more stable, and I'm
wondering if the -O flag is exposing a bug that I need to
fix. Are there some gcc flags that I should try that might
guide me in finding the problem? (I've already tried the
obvious -Wall which gives no warnings.)
If your code does something different with/without -g, then that's a
bug in gcc. -g shouldn't make any difference to the behaviour of your
program.
-g makes no difference.
If your code does somethig different with -O, that's possibly a gcc
bug but it's probably a bug in your code.
-OO and -O give different results.
If you use -fno-strict-aliasing and that makes a difference with -O,
then that's definitely a bug in your code.
I think you nailed it! With -fno-strict-aliasing, -O0 and -O
give identical results. I tried -fstrict-aliasing with -Wstrict-
aliasing=2, but gcc doesn't issue any warnings.
Any pointers for how to track this sort of thing down? What kind of
things should I look for?
Thanks!
--Michael
