[Bug tree-optimization/55071] New: "Horizontal sum" of bultin vectors

[vincenzo.innocente at cern dot ch]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55071

             Bug #: 55071
           Summary: "Horizontal sum" of bultin vectors
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: vincenzo.innocente@cern.ch


this
typedef float __attribute__( ( vector_size( 16 ) ) ) float32x4_t;
float  sum(float32x4_t x) {
  return x[0]+x[1]+x[2]+x[3];
}

does not use hadd 

on corei7
produces a quite inefficient

    movaps    %xmm0, %xmm2
    movaps    %xmm0, %xmm3
    shufps    $85, %xmm0, %xmm2
    movaps    %xmm2, %xmm1
    movaps    %xmm0, %xmm2
    addss    %xmm2, %xmm1
    unpckhps    %xmm0, %xmm3
    movaps    %xmm3, %xmm2
    shufps    $255, %xmm0, %xmm0
    addss    %xmm2, %xmm1
    addss    %xmm0, %xmm1
    movaps    %xmm1, %xmm0
    ret

for avx is a bit better (just thanks to the three arguments)

    vshufps    $85, %xmm0, %xmm0, %xmm2
    vaddss    %xmm0, %xmm2, %xmm1
    vunpckhps    %xmm0, %xmm0, %xmm2
    vshufps    $255, %xmm0, %xmm0, %xmm0
    vaddss    %xmm2, %xmm1, %xmm1
    vaddss    %xmm0, %xmm1, %xmm0