[Bug target/43514] use of SSE shift intrinsics introduces unnecessary moves to the stack and back

["kretz at kde dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #2 from kretz at kde dot org  2010-03-26 13:13 -------
BTW, I think you should consider this as a bug, not enhancement. Because if the
shift argument is >= (1 << 32) the result of _mm_sll_epi64 differs from the
expected result.
Thus the code GCC generates could potentially hide a bug, making the code
behave differently (but correct) when compiled by a different compiler.

Testcase:

#include <tmmintrin.h>

__m128i intrin()
{
    __m128i a = _mm_setzero_si128();
    a = _mm_cmpeq_epi8(a, a);
    __m128i count = _mm_sad_epu8(_mm_abs_epi8(a), _mm_setzero_si128()); // 8 0
... 8 0 ...
    count = _mm_slli_epi64(count, 29);
    return _mm_sll_epi64(a, count);
}

__m128i assem()
{
    register __m128i r asm("xmm0");
    asm(
            "pxor %%xmm1,%%xmm1\n\t"       // 0x0000
            "pcmpeqb %%xmm0,%%xmm0\n\t"    // 0xffff
            "pabsb %%xmm0,%%xmm2\n\t"      // 0x0101
            "psadbw %%xmm1,%%xmm2\n\t"     // 0x0008
            "psllq $29,%%xmm2\n\t"         // 0x0100
            "psllq %%xmm2,%%xmm0\n\t"
            :::"xmm0", "xmm1", "xmm2");
    return r;
}

int main()
{
    const __m128i a = intrin();
    const __m128i b = assem();
    return (_mm_movemask_epi8(_mm_cmpeq_epi32(a, b)) == 0xffff) ? 0 : -1;
}


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43514