Re: [PATCH] middle-end, i386, v3: Pattern recognize add/subtract with carry [PR79173]

[Jakub Jelinek <jakub@redhat.com>]

On Wed, Jun 14, 2023 at 04:45:48PM +0200, Uros Bizjak wrote:
> +;; Helper peephole2 for the addcarry<mode> and subborrow<mode>
> +;; peephole2s, to optimize away nop which resulted from uaddc/usubc
> +;; expansion optimization.
> +(define_peephole2
> +  [(set (match_operand:SWI48 0 "general_reg_operand")
> +       (match_operand:SWI48 1 "memory_operand"))
> +   (const_int 0)]
> +  ""
> +  [(set (match_dup 0) (match_dup 1))])
> 
> Is this (const_int 0) from a recent patch from Roger that introduced:

The first one I see is the one immediately above that:
;; Pre-reload splitter to optimize
;; *setcc_qi followed by *addqi3_cconly_overflow_1 with the same QI
;; operand and no intervening flags modifications into nothing.
(define_insn_and_split "*setcc_qi_addqi3_cconly_overflow_1_<mode>"
  [(set (reg:CCC FLAGS_REG)
        (compare:CCC (neg:QI (geu:QI (reg:CC_CCC FLAGS_REG) (const_int 0)))
                     (ltu:QI (reg:CC_CCC FLAGS_REG) (const_int 0))))]
  "ix86_pre_reload_split ()"
  "#"
  "&& 1"
  [(const_int 0)])

And you're right, the following incremental patch (I'd integrate it
into the full patch with
	(*setcc_qi_addqi3_cconly_overflow_1_<mode>, *setccc,
	*setcc_qi_negqi_ccc_1_<mode>, *setcc_qi_negqi_ccc_2_<mode>): Split
	into NOTE_INSN_DELETED note rather than nop instruction.
added to ChangeLog) passes all the new tests as well:

--- gcc/config/i386/i386.md	2023-06-14 12:21:38.668657604 +0200
+++ gcc/config/i386/i386.md	2023-06-14 17:12:31.742625193 +0200
@@ -7990,16 +7990,6 @@
    (set_attr "pent_pair" "pu")
    (set_attr "mode" "<MODE>")])
 
-;; Helper peephole2 for the addcarry<mode> and subborrow<mode>
-;; peephole2s, to optimize away nop which resulted from uaddc/usubc
-;; expansion optimization.
-(define_peephole2
-  [(set (match_operand:SWI48 0 "general_reg_operand")
-	(match_operand:SWI48 1 "memory_operand"))
-   (const_int 0)]
-  ""
-  [(set (match_dup 0) (match_dup 1))])
-
 (define_peephole2
   [(parallel [(set (reg:CCC FLAGS_REG)
 		   (compare:CCC
@@ -8641,7 +8631,8 @@
   "ix86_pre_reload_split ()"
   "#"
   "&& 1"
-  [(const_int 0)])
+  [(const_int 0)]
+  "emit_note (NOTE_INSN_DELETED); DONE;")
 
 ;; Set the carry flag from the carry flag.
 (define_insn_and_split "*setccc"
@@ -8650,7 +8641,8 @@
   "ix86_pre_reload_split ()"
   "#"
   "&& 1"
-  [(const_int 0)])
+  [(const_int 0)]
+  "emit_note (NOTE_INSN_DELETED); DONE;")
 
 ;; Set the carry flag from the carry flag.
 (define_insn_and_split "*setcc_qi_negqi_ccc_1_<mode>"
@@ -8659,7 +8651,8 @@
   "ix86_pre_reload_split ()"
   "#"
   "&& 1"
-  [(const_int 0)])
+  [(const_int 0)]
+  "emit_note (NOTE_INSN_DELETED); DONE;")
 
 ;; Set the carry flag from the carry flag.
 (define_insn_and_split "*setcc_qi_negqi_ccc_2_<mode>"
@@ -8669,7 +8662,8 @@
   "ix86_pre_reload_split ()"
   "#"
   "&& 1"
-  [(const_int 0)])
+  [(const_int 0)]
+  "emit_note (NOTE_INSN_DELETED); DONE;")
 \f
 ;; Overflow setting add instructions
 

	Jakub