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Subject: Re: [OMPI users] is loop unrolling safe for MPI logic?
From: Eugene Loh (eugene.loh_at_[hidden])
Date: 2010-07-17 12:14:11

Jeff Squyres wrote:

>On Jul 17, 2010, at 4:22 AM, Anton Shterenlikht wrote:
>>Is loop vectorisation/unrolling safe for MPI logic?
>>I presume it is, but are there situations where
>>loop vectorisation could e.g. violate the order
>>of execution of MPI calls?
>I *assume* that the intel compiler will not unroll loops that contain MPI function calls. That's obviously an assumption, but I would think that unless you put some pragmas in there that tell the compiler that it's safe to unroll, the compiler will be somewhat conservative about what it automatically unrolls.
More generally, a Fortran compiler that optimizes aggressively could
"break" MPI code.

That said, you may not need to worry about this in your particular case.