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From: XBR2D96D@DDATHD21.BITNET (Knobi der Rechnerschrat)
Newsgroups: comp.sys.sgi
Subject: Optimizer Questions
Message-ID: <8905180826.aa02829@SMOKE.BRL.MIL>
Date: 18 May 89 05:44:32 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 23

Hallo,

  I've got some questions about the optimizer levels for the C (and F77)
compiler on a 70GT.

  - compared to the -g flag that we use for pgm developement, using -O2
    results in a much greater speed increase than the step from -O2 to -O3.
    Taking the much greater compile/link times for -O3 into account, the
    question arises whether it is worth using -O3 or not. Especially, are
    there cases where -O3 is REALLY advantegous over -O2?

  - what is the difference between -O3 and -O4? -O4 seems not to be documented
    and it results in the same speedups than -O3.

Regards
Martin Knoblauch

TH-Darmstadt
Physical Chemistry 1 (soon: Center for Molecular Modelling)
Petersenstrasse 20
D-6100 Darmstadt, FRG

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