i386: Refactor new ix86_expand_carry to set the carry flag.

This patch refactors the three places in the i386.md backend that we
set the carry flag into a new ix86_expand_carry helper function, that
allows Jakub's recently added uaddc<mode>5 and usubc<mode>5 expanders
to take advantage of the recently added support for the stc instruction.

2023-06-18  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	* config/i386/i386-expand.cc (ix86_expand_carry): New helper
	function for setting the carry flag.
	(ix86_expand_builtin) <handlecarry>: Use it here.
	* config/i386/i386-protos.h (ix86_expand_carry): Prototype here.
	* config/i386/i386.md (uaddc<mode>5): Use ix86_expand_carry.
	(usubc<mode>5): Likewise.

3 files changed, 19 insertions, 14 deletions

diff --git a/gcc/config/i386/i386-expand.cc b/gcc/config/i386/i386-expand.cc
index 6a28b67..98c43c6 100644
--- a/gcc/config/i386/i386-expand.cc
+++ b/gcc/config/i386/i386-expand.cc
@@ -12646,6 +12646,21 @@ ix86_check_builtin_isa_match (unsigned int fcode,
   return (bisa & isa) == bisa && (bisa2 & isa2) == bisa2;
 }
 
+/* Emit instructions to set the carry flag from ARG.  */
+
+void
+ix86_expand_carry (rtx arg)
+{
+  if (!CONST_INT_P (arg) || arg == const0_rtx)
+    {
+      arg = convert_to_mode (QImode, arg, 1);
+      arg = copy_to_mode_reg (QImode, arg);
+      emit_insn (gen_addqi3_cconly_overflow (arg, constm1_rtx));
+    }
+  else
+    emit_insn (gen_x86_stc ());
+}
+
 /* Expand an expression EXP that calls a built-in function,
    with result going to TARGET if that's convenient
    (and in mode MODE if that's convenient).
@@ -13977,14 +13992,7 @@ rdseed_step:
       else
 	{
 	  /* Generate CF from input operand.  */
-	  if (!CONST_INT_P (op1))
-	    {
-	      op1 = convert_to_mode (QImode, op1, 1);
-	      op1 = copy_to_mode_reg (QImode, op1);
-	      emit_insn (gen_addqi3_cconly_overflow (op1, constm1_rtx));
-	    }
-	  else
-	    emit_insn (gen_x86_stc ());
+	  ix86_expand_carry (op1);
 
 	  /* Generate instruction that consumes CF.  */
 	  op1 = gen_rtx_REG (CCCmode, FLAGS_REG);
diff --git a/gcc/config/i386/i386-protos.h b/gcc/config/i386/i386-protos.h
index af01299..27fe73c 100644
--- a/gcc/config/i386/i386-protos.h
+++ b/gcc/config/i386/i386-protos.h
@@ -155,6 +155,7 @@ extern void ix86_expand_sse_movcc (rtx, rtx, rtx, rtx);
 extern void ix86_expand_sse_unpack (rtx, rtx, bool, bool);
 extern void ix86_expand_fp_spaceship (rtx, rtx, rtx);
 extern bool ix86_expand_int_addcc (rtx[]);
+extern void ix86_expand_carry (rtx arg);
 extern rtx_insn *ix86_expand_call (rtx, rtx, rtx, rtx, rtx, bool);
 extern bool ix86_call_use_plt_p (rtx);
 extern void ix86_split_call_vzeroupper (rtx, rtx);
diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index b8d2e3a..bfdd54f 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -8601,9 +8601,7 @@
     emit_insn (gen_addcarry<mode>_0 (operands[0], operands[2], operands[3]));
   else
     {
-      rtx op4 = copy_to_mode_reg (QImode,
-				  convert_to_mode (QImode, operands[4], 1));
-      emit_insn (gen_addqi3_cconly_overflow (op4, constm1_rtx));
+      ix86_expand_carry (operands[4]);
       pat = gen_rtx_LTU (<DWI>mode, cf, const0_rtx);
       pat2 = gen_rtx_LTU (<MODE>mode, cf, const0_rtx);
       emit_insn (gen_addcarry<mode> (operands[0], operands[2], operands[3],
@@ -8634,9 +8632,7 @@
   else
     {
       cf = gen_rtx_REG (CCCmode, FLAGS_REG);
-      rtx op4 = copy_to_mode_reg (QImode,
-				  convert_to_mode (QImode, operands[4], 1));
-      emit_insn (gen_addqi3_cconly_overflow (op4, constm1_rtx));
+      ix86_expand_carry (operands[4]);
       pat = gen_rtx_LTU (<DWI>mode, cf, const0_rtx);
       pat2 = gen_rtx_LTU (<MODE>mode, cf, const0_rtx);
       emit_insn (gen_subborrow<mode> (operands[0], operands[2], operands[3],