Runtime speed with GNU compilers

Stefano Gragnani
Mon Apr 14 14:36:00 GMT 1997

Thanks for the replies. I have compiled and runned another time the
code-example with various options, the results are:

1) without options ==> 2063 seconds
2) only with the '-O3' options (with the capital "O")  ==>  2362 seconds
3) with '-O3' + '-ffast-math'  ==> 113 seconds
4) with only '-ffast-math'  ==> about 2000 seconds.

Why with the '-O3' options the time is grater that without optimizations ? 
In the online documentation that I have read the '-O6' option is not
documented (only the '-O1', '-O2' and 'O3' are mentioned) but it is
accepted from the compiler: wich are "its optimizations"?
The '-ffast-math' is not aderent to the IEEE 754 arithmetic and therefore,
in general, it use is not recommended and is not good that g++ required it
(plus the '-O3' or the '-O6' option) to obtain the best result (113
seconds). (The Metrowerk compiler is aderent to the IEEE 754 and is result
is 125 seconds ...)
If the problems are the Cygnus libraries under NT, there are other
libraries for NT?

Stefano Gragnani

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