[Bug target/78563] New: SSE4.1 pmovzx shuffle pattern not recognized

["linux at carewolf dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78563

            Bug ID: 78563
           Summary: SSE4.1 pmovzx shuffle pattern not recognized
           Product: gcc
           Version: 6.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: linux at carewolf dot com
  Target Milestone: ---

An unpack pattern with 0 constant are neither folded nor recognized as a pmovzx
instruction.

SSE2 code:
_mm_unpacklo_epi32(X, _mm_setzero_si128())

GCC code:
__builtin_shuffle((__v4si)X, (__v4si)_mm_setzero_si128(), (__v4si){0, 4, 1,
5});

Will both produce the same result of an xor setting 0 and an unpack
instruction, while it could with SSE4.1 emit a pmozx instruction.

Note epi32 is just an example here used because it is most compact, this also
affects the 8 and 16 bit equivelents.

Looking in config/i386/i386.c it seems like there is no code in the
expand_vec_perm_* methods for detecting pmovzx patterns.