GCC compilations

[camlost]

Huh, I just debugged a problem that showed up depending on the compilation flags I set. For debugging, I don't compile for speed, and I compile with gcc (mingw32) with no flags. For release, I set -O3 for increased performance.

It turns out the problem was due to failure to initialize variables; do compilation flags affect variable initialization? Or was this just random?

[takkaria]

Huh, I just debugged a problem that showed up depending on the compilation flags I set. For debugging, I don't compile for speed, and I compile with gcc (mingw32) with no flags. For release, I set -O3 for increased performance.

It turns out the problem was due to failure to initialize variables; do compilation flags affect variable initialization? Or was this just random?

Higher levels of optimisation tend to create more compact code using cleverer reasoning about your code, so sometimes stuff like this happens where previously you were relying on some undefined behaviour and that behaviour changes. With enough warnings turned on this should be exceedingly rarre.

[camlost]

Higher levels of optimisation tend to create more compact code using cleverer reasoning about your code, so sometimes stuff like this happens where previously you were relying on some undefined behaviour and that behaviour changes. With enough warnings turned on this should be exceedingly rarre.

Fair enough. I usually fix a dozen or so of these errors when I get around to compiling on Linux. I should figure out why CodeBlocks is suppressing so many errors; it'd save me time in the long run.

[pav]

I'd suggest avoiding -O3 unless you do all the debugging with it (impractical). Certainly turn based text game does not need to worry about cpu performance. GCC is known to miscompile some otherwise perfectly valid C code with -O3, especially when output target is something else than i686/linux.

In the rather large open source C-written project I participate on (FreeBSD) we settled with -O2 -fno-strict-alignment as practical highest possible level. Even achieving that required some changes in code. Hiighest safe optimization in GCC is -O.

[Magnate]

Even the Linux kernel uses -O2 rather than -O3.