C++ Optimization with g++

[David.Carter-Hitchin]

Hi,

I haven't done a great deal of optimization, so apologies in advance for any
dumb or mis-directed questions.

I've got this nice little ~5,000 line c++ program at home which plots the
positions of planets and the Yale Bright Star Catalogue.

So far so good.

Scrolling an zooming are fine, but when I swtich the option on to display
dates (which involves rotating the bitmaps for the textstrings through 90
degrees) it runs "like a dog" and I'm not talking greyhound, more like a
three-legged dachshund.

So I tried putting -O[0123] on and ploop, the program is just warming up and
then it SEGV's.  It seems to be happening at the end of one function call
(which appears to run fine) or at the very start of another.  Compiling with
-g and running in gdb shows the point, which is just at the final } from the
last function that works successfully.

Ultimately I can reprogram the date stuff so I don't have to rotate the
dates on the fly (which is the way I should have done it originally), but
now I'm curious.

How can I find out why -O[0123] fails?  Is there a strategy I can follow
or doc I should read?  Is there a "simple" way of debugging my way out of
this situation, or is there no alternative to inspecting the assembly?

gcc version 2.9.something (not threaded).

All help and clues appreciated.

Many thanks,

David Carter-Hitchin,
GSD-Risk-IT, UBS Investment Bank