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>

diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index 8fb70eccd2495116c629f358fe916ba8822b11e0..f173423b33427ee8453c413db9d6977c0b8d11fb 100644 (file)
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -6761,10 +6761,7 @@
       if (TARGET_APX_NDD && <nf_applied>)
        return "%{nf%} add{<imodesuffix>}\t{%2, %1, %0|%0, %1, %2}";
       else
-       {
-         operands[3] = gen_rtx_PLUS (<MODE>mode, operands[1], operands[2]);
-         return "lea{<imodesuffix>}\t{%E3, %0|%0, %E3}";
-       }
+       return "#";
 
     case TYPE_INCDEC:
       if (operands[2] == const1_rtx)
@@ -7263,6 +7260,11 @@
       operands[1] = gen_lowpart (<LEAMODE>mode, operands[1]);
       operands[2] = gen_lowpart (<LEAMODE>mode, operands[2]);
     }
+  else
+    /* *lea<mode> and *add<mode>_1_nf have the same pattern, try_split
+       refuses to split an insn into itself, so just request
+       a new recog which will match *lea<mode> which comes first.  */
+    INSN_CODE (curr_insn) = -1;
 })
 
 ;; Convert add to the lea pattern to avoid flags dependency.