[Bug middle-end/100951] New: vec_duplicate<mode> leads to worse code

["hjl.tools at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100951

            Bug ID: 100951
           Summary: vec_duplicate<mode> leads to worse code
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hjl.tools at gmail dot com
                CC: rguenther at suse dot de
  Target Milestone: ---

After I added

;; Modes handled by broadcast patterns.
(define_mode_iterator INT_BROADCAST_MODE
  [(V64QI "TARGET_AVX512F") (V32QI "TARGET_AVX") V16QI
   (V32HI "TARGET_AVX512F") (V16HI "TARGET_AVX") V8HI
   (V16SI "TARGET_AVX512F") (V8SI "TARGET_AVX") V4SI
   (V8DI "TARGET_AVX512F") (V4DI "TARGET_64BIT") V2DI])

;; Broadcast from an integer.  NB: Enable broadcast only if we can move
;; from GPR to SSE register directly.  */
(define_expand "vec_duplicate<mode>"
  [(set (match_operand:INT_BROADCAST_MODE 0 "register_operand")
        (vec_duplicate:INT_BROADCAST_MODE
          (match_operand:<ssescalarmode> 1 "nonimmediate_operand")))]
  "TARGET_SSE2 && TARGET_INTER_UNIT_MOVES_TO_VEC"
{
  ix86_expand_integer_vec_duplicate (operands);
  DONE; 
})

to x86 backend, I got

[hjl@gnu-cfl-2 gcc]$ cat /tmp/x.c 
typedef short __attribute__((__vector_size__ (8 * sizeof (short)))) V;
V v, w;

void
foo (void)
{
  w = __builtin_shuffle (v != v, 0 < (V) {}, (V) {192} >> 5);
}
[hjl@gnu-cfl-2 gcc]$ ./xgcc -B./ -S /tmp/x.c
[hjl@gnu-cfl-2 gcc]$ cat x.s
        .file   "x.c"
        .text
        .globl  v
        .bss
        .align 16
        .type   v, @object
        .size   v, 16
v:
        .zero   16
        .globl  w
        .align 16
        .type   w, @object
        .size   w, 16
w:
        .zero   16
        .text
        .globl  foo
        .type   foo, @function
foo:
.LFB0:
        .cfi_startproc
        pushq   %rbp
        .cfi_def_cfa_offset 16
        .cfi_offset 6, -16
        movq    %rsp, %rbp
        .cfi_def_cfa_register 6
        movl    $0, %eax
        movd    %eax, %xmm0
        punpcklwd       %xmm0, %xmm0
        pshufd  $0, %xmm0, %xmm0
        movaps  %xmm0, w(%rip)
        nop
        popq    %rbp
        .cfi_def_cfa 7, 8
        ret
        .cfi_endproc
.LFE0:
        .size   foo, .-foo
        .ident  "GCC: (GNU) 12.0.0 20210607 (experimental)"
        .section        .note.GNU-stack,"",@progbits
[hjl@gnu-cfl-2 gcc]$ 

since middld-end leaves us with an unfolded constant CTOR.