[Bug target/114960] New: [12/13/14/15 Regression] fails to clean up vector casts

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114960

            Bug ID: 114960
           Summary: [12/13/14/15 Regression] fails to clean up vector
                    casts
           Product: gcc
           Version: 12.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: amonakov at gcc dot gnu.org
  Target Milestone: ---
            Target: x86_64-*-*

#include <immintrin.h>

__m128i f(__m128i dummy, __m128i x)
{
    __v16qi v = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 };
    return (__m128i)((__v16qi)x + v);
}

Starting from gcc-12, we get

        movdqa  .LC0(%rip), %xmm2
        paddb   %xmm1, %xmm2
        movdqa  %xmm2, %xmm0
        ret

while previously it was

        movdqa  .LC0(%rip), %xmm0
        paddb   %xmm1, %xmm0
        ret

Diverges in RTL land, starting in combine.