Mail Archives: djgpp/1997/03/31/10:51:10
On Sat, 29 Mar 1997, Dan Hirschberg wrote:
> The same program compiled with the newer compiler had much worse
> performance (about 50% worse) on both my 486 and my Pentium Pro.
> The performance was even worse with -O2. I was able to improve
> the performance somewhat by using -O1 and adding a few of the
> -f options (found by reading the info file on gcc), but still about
> 40% worse than under the 2.6.0 version.
>
> Is this a common experience?
No. People who tested this report that the optimization quality is the
same, and sometimes slightly better in 2.7.2.1.
> Could this be a result of my program having particular characteristics?
Yes. But first, be sure to read section 14.2 of the DJGPP FAQ list. The
effect of some optimizations switches is different between different GCC
versions, and that section tells you how to choose the best combination
for the new version.
If the advice there don't help, I suggest reading section 14.5 which
might give you ideas about possible causes of slow-down which are
specific to your program. If that doesn't unlock the problem either,
tell more about what does your program do and in what environment (DOS?
Windows? NT?) do you run the two different versions. Profiling the
program might also point to the problem spots.
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