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From: "noloader at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/66943] New: GCC warns of Unknown Pragma for OpenMP, even though it support it.
Date: Mon, 20 Jul 2015 08:00:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66943

            Bug ID: 66943
           Summary: GCC warns of Unknown Pragma for OpenMP, even though it
                    support it.
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: noloader at gmail dot com
  Target Milestone: ---

The following source code results in a slew of Unknown Pragma messages. The
problem is, GCC supports OpenMP. GCC responds properly to -fopenmp, and even
defines _OPENMP when it encounters -fopenmp.

This is related to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53431, and
managing warnings with pragmas when using -Wall. The relation to 53431 is: I
can't seem to get "pragma GCC diagnostic" to work to ignore the warnings when
-Wall is in effect.

// Defines GCC_DIAGNOSTIC_AWARE if GCC 4.7 or above.
#define GCC_DIAGNOSTIC_AWARE 1

#if GCC_DIAGNOSTIC_AWARE
# pragma GCC diagnostic ignored "-Wunknown-pragmas"
#endif

...
Integer ModularRoot(const Integer &a, const Integer &dp, const Integer &dq,
                    const Integer &p, const Integer &q, const Integer &u)
{
    Integer p2, q2;
    #pragma omp parallel
        #pragma omp sections
        {
            #pragma omp section
                p2 = ModularExponentiation((a % p), dp, p);
            #pragma omp section
                q2 = ModularExponentiation((a % q), dq, q);
        }
    return CRT(p2, p, q2, q, u);
}
...

**********

To duplicate:

    git clone https://github.com/weidai11/cryptopp.git cryptopp-warn
    cd cryptopp-warn
    export CXXFLAGS="-g2 -O3 -DNDEBUG -Wall"
    make