Re: gcc 3.1 slower than 2.95?

[Harold L Hunt <huntharo at msu dot edu>]

Marcus,

First, this is probably way off topic for the Cygwin list.  You should be
asking on the gcc lists.

However, I can make one comment.  In a scientific experiment you only change
one variable each time.  However, you changed two:

> -> gcc 2.95 
> g++ -O2 -mcpu=pentium -Wall settest.cpp -lwinmm
> 
> -> gcc 3.1
> g++ -O3 -mcpu=pentium -Wall settest.cpp -lwinmm

You changed both the compiler (from 2.95 to 3.1) and the optimization flag
(from -O2 to -O3).  Don't do that.  Make both tests at -O2 or -O3.  The -O2
flag seems to be about as high as anyone goes without doing some extensive
analysis on their own to determine if -O3 would be of any benefit.  Also, the
-O3 flag can do things that make the code size much larger which can negate
the effect of a processor cache, etc.  Stick with -O2 for both tests.


Harold

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