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Re: detection and support of OpenMP

From: Paul Eggert
Subject: Re: detection and support of OpenMP
Date: Thu, 17 May 2007 08:52:02 -0700
User-agent: Gnus/5.110006 (No Gnus v0.6) Emacs/21.4 (gnu/linux)

What are the consequences of compiling with -fopenmp etc.?  Can you
link modules compiled with -fopenmp, with modules that are not
compiled with -fopenmp?  Does -fopenmp hurt performance for apps that
don't need it?

How would one use OPENMP_CFLAGS?  Does -fopenmp need to be added to
both CFLAGS and CPPFLAGS?  Is that why it's not merely put into
CFLAGS?  This is related to our more-general problem that compiler
options like -m64 don't properly belong in either CFLAGS or CPPFLAGS,
which means people typically work around the problem with "CC=gcc -m64".
This is not a problem with OpenMP per se, but OpenMP sounds like it
makes things worse.

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