[PATCH, rs6000] Add a combine pattern for CA minus one [PR95737]

[HAO CHEN GUI]

Hi,
   This patch adds a combine pattern for "CA minus one". As CA only has two
values (0 or 1), we could convert following pattern
      (sign_extend:DI (plus:SI (reg:SI 98 ca)
                (const_int -1 [0xffffffffffffffff]))))
to
       (plus:DI (reg:DI 98 ca)
            (const_int -1 [0xffffffffffffffff])))
    With this patch, it eliminates one unnecessary sign extend. Also in rs6000,
regclass of CA register is set to NO_REGS. So CA is not in hard register set
and it can't match register_operand. The patch changes it to any_operand.

    Bootstrapped and tested on powerpc64-linux BE and LE with no regressions.
Is this okay for trunk? Any recommendations? Thanks a lot.

ChangeLog
2022-01-19 Haochen Gui <guihaoc@linux.ibm.com>

gcc/
	* config/rs6000/predicates.md (ca_operand): Match any_operand as CA
	register is not in hard register set.
	* config/rs6000/rs6000.md (extenddi_ca_minus_one): Define.

gcc/testsuite/
	* gcc.target/powerpc/pr95737.c: New.


patch.diff
diff --git a/gcc/config/rs6000/predicates.md b/gcc/config/rs6000/predicates.md
index c65dfb91f3d..cd2ae1dc8e0 100644
--- a/gcc/config/rs6000/predicates.md
+++ b/gcc/config/rs6000/predicates.md
@@ -188,7 +188,7 @@ (define_predicate "vlogical_operand"

 ;; Return 1 if op is the carry register.
 (define_predicate "ca_operand"
-  (match_operand 0 "register_operand")
+  (match_operand 0 "any_operand")
 {
   if (SUBREG_P (op))
     op = SUBREG_REG (op);
diff --git a/gcc/config/rs6000/rs6000.md b/gcc/config/rs6000/rs6000.md
index 6ecb0bd6142..f1b09aad3b5 100644
--- a/gcc/config/rs6000/rs6000.md
+++ b/gcc/config/rs6000/rs6000.md
@@ -2358,6 +2358,21 @@ (define_insn "subf<mode>3_carry_in_xx"
   "subfe %0,%0,%0"
   [(set_attr "type" "add")])

+(define_insn_and_split "*extenddi_ca_minus_one"
+  [(set (match_operand:DI 0 "gpc_reg_operand")
+	(sign_extend:DI (plus:SI (match_operand:SI 1 "ca_operand")
+				 (const_int -1))))]
+  ""
+  "#"
+  ""
+  [(parallel [(set (match_dup 0)
+		   (plus:DI (match_dup 2)
+			    (const_int -1)))
+	      (clobber (match_dup 2))])]
+{
+  operands[2] = copy_rtx (operands[1]);
+  PUT_MODE (operands[2], DImode);
+})

 (define_insn "@neg<mode>2"
   [(set (match_operand:GPR 0 "gpc_reg_operand" "=r")
diff --git a/gcc/testsuite/gcc.target/powerpc/pr95737.c b/gcc/testsuite/gcc.target/powerpc/pr95737.c
new file mode 100644
index 00000000000..94320f23423
--- /dev/null
+++ b/gcc/testsuite/gcc.target/powerpc/pr95737.c
@@ -0,0 +1,10 @@
+/* PR target/95737 */
+/* { dg-do compile { target lp64 } } */
+/* { dg-options "-O2 -mdejagnu-cpu=power8" } */
+/* { dg-final { scan-assembler-not {\mextsw\M} } } */
+
+
+unsigned long long negativeLessThan (unsigned long long a, unsigned long long b)
+{
+   return -(a < b);
+}