[Bug tree-optimization/56253] New: fp-contract does not work with SSE and AVX FMAs (neither FMA4 nor FMA3)

[kretz at kde dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56253

             Bug #: 56253
           Summary: fp-contract does not work with SSE and AVX FMAs
                    (neither FMA4 nor FMA3)
    Classification: Unclassified
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: kretz@kde.org


Take the following testcase:

#include <immintrin.h>
__m256 foo(__m256 a, __m256 b, __m256 c)
{  
    return _mm256_add_ps(_mm256_mul_ps(a, b), c);
}
__m128 foo(__m128 a, __m128 b, __m128 c)
{  
    return _mm_add_ps(_mm_mul_ps(a, b), c);
}
float foo(float a, float b, float c)
{  
    return a * b + c;
}

compiled with 'g++ -O3 -mfma -ffp-contract=fast -fabi-version=0 -c' only the
third function uses fmas (same for -mfma4). The SSE and AVX variant should make
the same contraction as is implemented for scalar operations.