[Bug target/104412] New: [Aarch64] Failure to optimize vector initialization from int64s

[gabravier at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104412

            Bug ID: 104412
           Summary: [Aarch64] Failure to optimize vector initialization
                    from int64s
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gabravier at gmail dot com
  Target Milestone: ---

#include <stdint.h>

typedef int64_t v2i64 __attribute__((vector_size(16)));

v2i64 _mm_set_epi64x(int64_t i1, int64_t i2)
{
    union {
        int64_t data[2];
        v2i64 v;
    } d = {.data = {i2, i1}};
    return d.v;
}

With -O3, AArch64 GCC outputs this:

_mm_set_epi64x(long, long):
  sub sp, sp, #16
  stp x1, x0, [sp]
  ldr q0, [sp]
  add sp, sp, 16
  ret

LLVM instead outputs this:

_mm_set_epi64x(long, long):
  fmov d0, x1
  mov v0.d[1], x0
  ret