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From: t19@nikhefh.nikhef.nl (Geert J v Oldenborgh)
Newsgroups: comp.lang.fortran
Subject: why does optimization take so long ?
Message-ID: <1236@nikhefh.nikhef.nl>
Date: 20 May 91 19:58:03 GMT
Sender: t19@nikhef.nl (Geert J v Oldenborgh)
Organization: Nikhef-H, Amsterdam (the Netherlands).
Lines: 15

I am curious whether any of you know why compiling certain routines with a -O 
flag takes a semi-infinite amount of time on certain computers (Apollo DN1000, 
Sun Fortran 1.3.1) (i.e. I killed compilation after a few hours CPU time for a 
single routine).  The code in question is generated by a computer algebra 
program, and looks like this

      qqgg= n1i*n2i*pbqi*ptqi * (  - 2*pnpe*pbpt**2*qk + 2*pnpe*
     + qk*mb2*mt2 + 2*pnpb*pepb*pbpt*qk - 2*pnpb*pepb*qk*mt2 + 2*
     + pnpb*pept*pbpt*qk + 4*pnpb*pept*pbpt**2 - pnpb*pept*qk*mb2 - 
      ...400 similar lines...	

As a lot of the time is spent here I'd like to be able to optimize it.

Geert Jan van Oldenborgh
gj@hep.physik.uni-muenchen.de