On Fri, May 29, 2026 at 09:47:45AM +0200, Jakub Jelinek wrote:
> 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.
I've dropped the ball on this sorry.
I've tested following patch on the trunk on x86_64-linux and i686-linux,
ok for trunk?
2026-06-02 Jakub Jelinek <[email protected]>
PR target/125469
* config/i386/i386.md (*add<mode>_1<nf_name>): Revert 2026-05-28
change.
(define_split from *add<mode>_1_nf to *lea<mode>): Set INSN_CODE
to -1 if <LEAMODE> and <MODE> are the same.
--- gcc/config/i386/i386.md.jj 2026-06-01 23:00:32.078971912 +0200
+++ gcc/config/i386/i386.md 2026-06-01 23:04:41.017838244 +0200
@@ -6760,10 +6760,7 @@ (define_insn "*add<mode>_1<nf_name>"
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)
@@ -7262,6 +7259,11 @@ (define_split
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.
Jakub
