Newsgroups: comp.sys.apollo
Path: utzoo!utgpu!news-server.csri.toronto.edu!helios.physics.utoronto.ca!alchemy.chem.utoronto.ca!system
From: system@alchemy.chem.utoronto.ca (System Admin (Mike Peterson))
Subject: Re: ftn 10.7 and f77 - problem
Message-ID: <1991Apr9.181118.25404@alchemy.chem.utoronto.ca>
Organization: University of Toronto Chemistry Department
References: <1991Apr9.043538.4195@metro.ucc.su.OZ.AU>
Date: Tue, 9 Apr 1991 18:11:18 GMT

In article <1991Apr9.043538.4195@metro.ucc.su.OZ.AU> moss_r@summer.chem.su.oz.au (Richard Moss) writes:
>I was using "f77 -W0,-opt 4".  If I used "f77 -W0,-opt 4,-xrs" instead
>everything was fine and dandy again. 

I am assuming you actually did
     f77 "-W0,-opt 4,-xrs"
or something else to quote the blank in the option (otherwise f77 won't
see the '-opt 4' but sees '-opt' which defaults to '-opt 3').

>Using /usr/apollo/lib/ftn by hand ( without -xrs ) also worked fine.

According to the manual, 'xrs' is the default so it shouldn't matter.
What 'opt' did you specify and how?

>What does f77 do that stuffs up the higher optimisation levels ?  

See your manual, pp. 6-22 to 6-32. We have found some problems with 
'-opt 3' but most programs that fail do so at compile time with "backend
failures" (unless the program uses complex variables, when it will
probably compile but give wrong results at -O). We don't bother with
'-opt 4' except in special cases, since more programs give wrong answers
and we don't see much speedup on general (usually sloppy :-)) codes.

At 10.8, '-opt 4' or '-O4' can in-line your subroutines for better
optimization.
-- 
Mike Peterson, System Administrator, U/Toronto Department of Chemistry
E-mail: system@alchemy.chem.utoronto.ca
Tel: (416) 978-7094                  Fax: (416) 978-8775