[Bug target/125469] ICE: in final_scan_insn_1, at final.cc:2823 could not split insn {*adddi_1_nf} with -Ofast -mapx-features=nf

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125469

--- Comment #7 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-16 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:d2e6ca510a713db8cfefb1bc8d3a3fa1b9402f2f

commit r16-9188-gd2e6ca510a713db8cfefb1bc8d3a3fa1b9402f2f
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Mon Jun 29 13:06:06 2026 +0200

    i386: Fix up *add<mode>_1<nf_name> [PR125469]

    I've debugged this now on the 16 branch where my patch is not present.
    The
    (define_split
      [(set (match_operand:SWI 0 "register_operand")
            (plus:SWI (match_operand:SWI 1 "register_operand")
                      (match_operand:SWI 2 "<nonmemory_operand>")))]
      "TARGET_APX_NF && reload_completed
       && ix86_lea_for_add_ok (insn, operands)"
      [(set (match_dup 0)
            (plus:<LEAMODE> (match_dup 1) (match_dup 2)))]
    {
      if (<MODE>mode != <LEAMODE>mode)
        {
          operands[0] = gen_lowpart (<LEAMODE>mode, operands[0]);
          operands[1] = gen_lowpart (<LEAMODE>mode, operands[1]);
          operands[2] = gen_lowpart (<LEAMODE>mode, operands[2]);
        }
    })
    splitter there is matched, including ix86_lea_for_add_ok on
    (insn 12 10 13 2 (set (reg:DI 2 cx [108])
            (plus:DI (reg:DI 0 ax [orig:104 s ] [104])
                (reg:DI 5 di [ _2+8 ]))) "apx-nf-pr125469.c":10:5 288
{*adddi_1_nf}
         (nil))
    But then goes into:
     rtx_insn *
     gen_split_138 (rtx_insn *curr_insn ATTRIBUTE_UNUSED, rtx *operands)
     {
       if (dump_file)
         fprintf (dump_file, "Splitting with gen_split_138 (i386.md:7136)\n");
       start_sequence ();
     #define FAIL return (end_sequence (), nullptr)
     #define DONE return end_sequence ()
     #line 7144 "../../gcc/config/i386/i386.md"
     {
       if (DImode != DImode)
         {
           operands[0] = gen_lowpart (DImode, operands[0]);
           operands[1] = gen_lowpart (DImode, operands[1]);
           operands[2] = gen_lowpart (DImode, operands[2]);
         }
     }
     #undef DONE
     #undef FAIL
       static const uint8_t expand_encoding[] = {
          0x01, 0x1f, 0x01, 0x00, 0x3b, 0x12, 0x01, 0x01,
          0x01, 0x02
       };
       return complete_seq (expand_encoding, operands);
     }
    That returns
    (insn 37 0 0 (set (reg:DI 2 cx [108])
            (plus:DI (reg:DI 0 ax [orig:104 s ] [104])
                (reg:DI 5 di [ _2+8 ]))) -1
         (nil))
    But then in try_split we have:
       /* Avoid infinite loop if any insn of the result matches
          the original pattern.  */
       insn_last = seq;
       while (1)
         {
           if (INSN_P (insn_last)
               && rtx_equal_p (PATTERN (insn_last), pat))
             return trial;
    which is a must, otherwise we'd try to split the newly created insn again
    and again succeed in splitting it and so forth forever.

    So, this patch instead sets INSN_CODE to -1 in the splitter to indicate
    that it needs to be re-recognized.

    2026-06-29  Jakub Jelinek  <jakub@redhat.com>

            PR target/125469
            * config/i386/i386.md (*add<mode>_1<nf_name>): Revert 2026-05-28
            changes.
            (define_split from *add<mode>_1_nf to *lea<mode>): Set INSN_CODE
            to -1 if <LEAMODE> and <MODE> are the same.

    Reviewed-by: Uros Bizjak <ubizjak@gmail.com>
    (cherry picked from commit c474154437b7ea4e3c3570c045f2e9e737ac8b9e)