[Bug tree-optimization/102056] New: VEC_PERM_EXPR of different sizes are not combined

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102056

            Bug ID: 102056
           Summary: VEC_PERM_EXPR of different sizes are not combined
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

take this on x86_64 with -mavx2:
#define vector __attribute__((vector_size(16)))

vector char g(vector char a)
{
    return __builtin_shuffle(a,(vector
char){15,14,13,12,11,10,9,8,7,6,5,4,3,2,1, 0});
}

vector char g1(vector char a)
{
    vector char t= __builtin_shuffle(a,(vector
char){7,6,5,4,3,2,1,0,15,14,13,12,11,10,9,8,});
    vector long long t1 = (vector long long)t;
    t1 = __builtin_shuffle(t1, (vector long long){1,0});
    return (vector char)t1;
}
--- CUT ---
We get:
g:
        .cfi_startproc
        vpshufb .LC0(%rip), %xmm0, %xmm0
        ret
g1:
        vpshufb .LC1(%rip), %xmm0, %xmm0
        vpalignr        $8, %xmm0, %xmm0, %xmm0
        ret

But really these two functions are the same.