[PATCH v2, rs6000] Add a combine pattern for CA minus one [PR95737]

[HAO CHEN GUI via Gcc-patches]

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, one unnecessary sign extend is eliminated.

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

ChangeLog
2022-01-20 Haochen Gui <guih...@linux.ibm.com>

gcc/
        * 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/rs6000.md b/gcc/config/rs6000/rs6000.md
index 6ecb0bd6142..1d8b212962f 100644
--- a/gcc/config/rs6000/rs6000.md
+++ b/gcc/config/rs6000/rs6000.md
@@ -2358,6 +2358,19 @@ (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" "=r")
+       (sign_extend:DI (plus:SI (reg:SI CA_REGNO)
+                                (const_int -1))))]
+  ""
+  "#"
+  ""
+  [(parallel [(set (match_dup 0)
+                  (plus:DI (reg:DI CA_REGNO)
+                           (const_int -1)))
+             (clobber (reg:DI CA_REGNO))])]
+  ""
+)

 (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);
+}