With and Without gcc OMP

[Orna Agmon Ben-Yehuda]

Hi All,

I am trying to compile the same code using gcc 4.2, which has gomp (gnu open mp 
- a library for automatic thread paralelization) already in it. I want the code 
to still compile cleanly (using -Werror) without openMP at all, because it is 
said that there is a performance penalty to compiling with openMP, even if not 
using it (that is, defining the number of threads at runtime to be 1).

I would also like to be able to still compile the code cleanly on prior 
versions of gcc, specifically on 3.4.* which I currently use.

The problem is that in order to use OMP I need to insert pragmas such as

#pragma omp for

And both gcc 3.4.4 and gcc 4.2 without the -fopenmp flag complain about 
ignoring a pragma for each such line.

I tried hiding the pragma using a construct such as

#ifdef HAVE_OMP
#define MYOMP(C) C
#else
#define MYOMP(C)
#endif

But it seems that pragmas are parsed before defines are parsed, so this 
construct creates multiple errors when used:

MYOMP(#pragma omp for)

In gcc 4.2 there are two -W switches to control pragma warnings:
-Wno-pragmas - controls errors in known pragmas
and
-Wunknown-pragmas
To create extra warnings for pragmas in system headers.

Those do not exist in gcc 3.4, and anyway do not help me even in gcc 4.2 
without -fopenmp, because the warnings I get are included in -Wall, which I 
wish to use when I compile (I already have a compilation line of several lines 
length, imagine what would happen if I did NOT use -Wall).

Any ideas?

Happy Sukkot,

Orna.
(Haifuxers - sorry for double posting - I am still waiting for my mail to 
arrive the mailing list...)

--
Orna Agmon Ben-Yehuda http://ladypine.org/
ICQ: 348759096


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