To: djgpp AT delorie DOT com
cc: dan AT verity DOT ICS DOT UCI DOT EDU
Subject: gcc optimize performance, V2.7.2.1 versus V2.6.0
Reply-To: Dan Hirschberg <dan AT ics DOT uci DOT edu>
Date: Sat, 29 Mar 1997 11:45:54 -0800
From: Dan Hirschberg <dan AT verity DOT ICS DOT UCI DOT EDU>
Message-ID:  <9703291145.aa19506@paris.ics.uci.edu>

I compiled a program on my 486 (using gcc -O)
under djgpp version 2.6.0 [which uses go32]
and again on my Pentium Pro (using gcc -O  and later gcc -O2)
under djgpp version 2.7.2.1 [which uses dpmi]
and ran all of the executables on both machines.
I obtained disheartening results.

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?
Could this be a result of my program having particular characteristics?

dan