Re: gcc 3.2 makes slower code

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Article #422

#422

From: Jeffrey Cunningham
Date: Mon, 25 Nov 2002 19:01

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Okay, here's what I've come up with so far. There is a core of calculations my
code must perform thousands of times. I benchmarked just this core with and
without I/O, on gcc 2.95 and 3.2, using -O2 and -O3 on the latter. Here
are the results:

gcc 2.95 with IO: .20 minutes
gcc 2.95 w/o IO: .18 minutes
gcc 3.2 -O3 with IO: .32 minutes
gcc 3.2 -O3 w/o IO: .27 minutes
gcc 3.2 -O2 w/o IO: .27 minutes

conclusions: (1) it isn't the I/O. The "slowdown factor" going to gcc 3.2
is x1.6 with I/O and x1.5 without. And (2) it makes no difference to these
calculations (intensive floating point vector operations) whether I use
-O3 or -O2. 

I haven't tried any of the more esoteric optimization tricks yet. But at
this point I'm somewhat alarmed by the loss in performance. 

-Jeff

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From: "Jeffrey Cunningham" <jeffrey@cunningham.net>
Subject: Re: gcc 3.2 makes slower code
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