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Message from discussion Global array operations: a performance hit?
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Dennis Wassel  
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 More options Jun 17 2008, 5:21 pm
Newsgroups: comp.lang.fortran
From: Dennis Wassel <dennis.was...@googlemail.com>
Date: Tue, 17 Jun 2008 14:21:53 -0700 (PDT)
Local: Tues, Jun 17 2008 5:21 pm
Subject: Re: Global array operations: a performance hit?
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On 17 Jun., 22:41, ka...@troutmask.apl.washington.edu (Steven G.

Kargl) wrote:
> In article <9e1269be-de8c-4971-857d-e95bf639d...@i76g2000hsf.googlegroups.com>,

> For starters, you can see what gfortran does by using the
> -fdump-tree-original option.  Try it with

> subroutine po(x,y)
>    real x(3,3), y(3,3)
>    x = 1.
>    y = 0.
>    x = matmul(x,y)
> end subroutine po

> If you're really curious about the internal goop, use -fdump-tree-all.

This sounds dangerously like "don't do this, unless you *really* want
to".
Right'o, gimme something to fill my umpteen MBs of terminal buffer :)

> There is currently no warning and AFAIK no request for such a feature.
> gfortran has fairly decent dependency analysis, but in certain situation
> it will err on the safe side and generate a temporary array even if
> it isn't necessarily needed.

There is a feature request -- PR 29952 created by Tobias in late 2006:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29952

I think this would be a cool feature, but then again, fixing bugs is
probably more important right now.


 
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