Re: -O2 vs -O3

From: Rask Ingemann Lambertsen (
Date: Thu May 25 2000 - 13:17:25 EST

Den 24-Maj-00 20:13:22 skrev Dave Jones fĝlgende om "Re: -O2 vs -O3":

>During the early development of Powertweak I set the Makefile files to
>compile some routines with -O3 instead of -O2. I then spent hours looking for
>a bug which wasn't there. The optimiser was over-zealous, and removed a
>pointer assignment.

>So I guess -O2 implies that we use only the known-to-be-safe optimisations.

   It doesn't. None of the -Ox options turn on unsafe optimisations. While
compiler bugs do occasionally happen, most of the time it is the programmer
that violated the rules.

>On a sidenote, the optimiser in egcs 2.91.66 still generates bugged code in
>some situations which can only be worked around by setting -O0
>(Example available upon request)

   Egcs 2.91.66 is old. Hopefully you reported the bug to the GCC team.


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