On 4/22/07, Jack Andrews <effbiae@xxxxxxxxx> wrote:
hi guys, i write to you direct because i can't find the relevant mailing list for help with the mmintrin functions. there's a thread at: http://gcc.gnu.org/ml/gcc-help/2007-04/msg00201.html that details my problems. i want to sum an array of longs using mmx. i use the functions: _mm_set_pi32 and _m_paddd but the resultant binary contains significantly less efficient code than inline asm or even plain C ( for(i=0;i<n;i++)total+=a[i]; ). here's the relevant function: simd_mmintrin(n, is) I *is; { __m64 q,r; I i; _m_empty(); q=_m_from_int(0); for (i=0; i < n; i+=W) { r=_mm_set_pi32(is[i],is[i+1]); q=_m_paddd(q,r); } union {long a[2];__m64 m;}u; u.m=q; return u.a[0]+u.a[1]; } and the rest of the code and a shell script to run it is in the thread above.
You should do a bugreport. I suspect that we cannot combine _mm_set_pi32(is[i],is[i+1]) to a movq as you do in the asm and that we have non-optimal register allocation. Richard.
