[Bug tree-optimization/117735] New: SLP dot_prod opportunity in 525.x264_r

[rguenth at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117735

            Bug ID: 117735
           Summary: SLP dot_prod opportunity in 525.x264_r
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rguenth at gcc dot gnu.org
  Target Milestone: ---

525.x264_r has

typedef unsigned char uint8_t;
void mc_chroma( uint8_t *dst, int i_dst_stride,
                       uint8_t *src, int i_src_stride,
                       int mvx, int mvy,
                       int i_width, int i_height )
{
    uint8_t *srcp;

    int d8x = mvx&0x07;
    int d8y = mvy&0x07;
    int cA = (8-d8x)*(8-d8y);
    int cB = d8x    *(8-d8y);
    int cC = (8-d8x)*d8y;
    int cD = d8x    *d8y;

    src += (mvy >> 3) * i_src_stride + (mvx >> 3);
    srcp = &src[i_src_stride];

    for( int y = 0; y < i_height; y++ )
      {
        for( int x = 0; x < i_width; x++ )
          dst[x] = ( cA*src[x]  + cB*src[x+1] + cC*srcp[x] + cD*srcp[x+1] + 32
) >> 6;
        dst  += i_dst_stride;
        src   = srcp;
        srcp += i_src_stride;
      }
}

where the inner loop could use two dot_prodvNhiv2Nqi - iff we had a SLP
pattern recognizing this and iff we'd narrow the invariants to [us]char
(pattern recog demotes the multiply to HImode, range info on c[ABCD]
indicates they fit in QImode).

And iff we'd nail down which lanes get summed for dot_prod (other related
summing optabs have the same unsepcifiedness here, making them only useful
for reductions where we end up summing the result lanes).