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From: calvin@dinkum.wpd.sgi.com (Calvin H. Vu)
Newsgroups: comp.sys.sgi
Subject: Re: FORTRAN program optimisation
Message-ID: <41004@sgi.sgi.com>
Date: 25 Aug 89 22:06:00 GMT
References: <89Aug25.093608edt.57688@ugw.utcs.utoronto.ca>
Sender: calvin@dinkum.wpd.sgi.com
Organization: Silicon Graphics, Inc., Mountain View, CA
Lines: 47

In article <89Aug25.093608edt.57688@ugw.utcs.utoronto.ca>, LEONARDZ@UOGUELPH.BITNET ("Len Zaifman  UoGuelph 824-4120 xt 6566", 519) writes:
> 
>      1 . I am trying to compile some fortran code with optimisation. At O2 ,
>         several routines ( this program has several hundred  ) hit the error
>        not optimised beacuase global tables are not large enough, use
>         Olimit > nnn where nnn is some number larger than 500. The question
>         is , does it hurt the performance of the program , or the program
>         size to compile  with Olimit nnn,where nnn is greater than the largest
>         reported size required, for all the routines , whether they need the
>         space or not ?? The program is large enough as it is , and I am trying
>         to enhance its runtime execution speed as much as possible.
	The number specified in the -Olimit option is used to set up the
	internal table inside the optimizer.   It will not adversely effect the 
	runtime speed nor the size of your program (other than the fact that
	your program will be smaller and run faster if optimized).   The only
	bad effect is that the bigger the number, the more memory space will
	be used by the optimizer, and your program may take longer to compile.

>       To that end I would also like someone from SGI to comment on the
>     advisability of using O3. I was told that at the moment this level of
>     optimisation is unsafe. Is that true , and what performance enhancement
>     is expected over O2 optimisation ?? 
	The reason we don't recommend -O3 level is because it fails some of
	our internal QA tests.   It provides about 10% improvement over -O2
	level, depending on your application.

>     Also, for a very large program such
>     as this what are the recommended analysis tools on IRIX to help
>     optimise the performance(hopefully without source code changes ). I am
>     looking for tools which help restructure the binary(loaded) code to
>     enhance performance.
> 
	Sorry we don't have any tools that can do optimization on loaded
	binary code.
	You can use 'prof' and 'pixie' to figure out all the places in your
	program that may need to be changed for faster execution.

>    2. On the user interface side , I see a need for easier command recall
>       than using !nnn to recall a command. Recently I worked on an Apollo
>       where command recall and editting was available through mouse
>       highlighting, cutting and pasting (ie like a mac). Can this be done
>       in IRIX now (3.1 x level)? will it be available at 3.2 ?? In
>       Workspace ??
> 
	We have cut & paste in 3.2.
>                                                           Regards,
>                                                           Len Zaifman