[Bug rtl-optimization/56766] Fails to combine (vec_select (vec_concat ...)) to (vec_merge ...)

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56766

--- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> ---
So it works with

(define_insn "sse3_addsubv2df3"
  [(set (match_operand:V2DF 0 "register_operand" "=x,x")
        (vec_select:V2DF
          (vec_concat:V4DF
            (plus:V2DF
              (match_operand:V2DF 1 "register_operand" "0,x")
              (match_operand:V2DF 2 "nonimmediate_operand" "xm,xm"))
            (minus:V2DF (match_dup 2) (match_dup 1)))
          (parallel [(const_int 0) (const_int 3)])))]

but not with

(define_insn "sse3_addsubv2df3"
  [(set (match_operand:V2DF 0 "register_operand" "=x,x")
        (vec_select:V2DF
          (vec_concat:V4DF
            (plus:V2DF
              (match_operand:V2DF 1 "register_operand" "0,x")
              (match_operand:V2DF 2 "nonimmediate_operand" "xm,xm"))
            (minus:V2DF (match_dup 1) (match_dup 2)))
          (parallel [(const_int 0) (const_int 3)])))]