RISC-V: Handle "(a & twobits) == singlebit" in branches using Zbs

Use Zbs when generating a sequence for
   "if ((a & twobits) == singlebit) ..."
that can be expressed as
   bexti + bexti + andn.

gcc/ChangeLog:

	* config/riscv/bitmanip.md
	(*branch<X:mode>_mask_twobits_equals_singlebit):
	Handle "if ((a & T) == C)" using Zbs, when T has 2 bits set and C
	has one	of these tow bits set.
	* config/riscv/predicates.md (const_twobits_not_arith_operand):
	New predicate.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/zbs-if_then_else-01.c: New test.

3 files changed, 67 insertions, 0 deletions

diff --git a/gcc/config/riscv/bitmanip.md b/gcc/config/riscv/bitmanip.md
index 681498a..58bac72 100644
--- a/gcc/config/riscv/bitmanip.md
+++ b/gcc/config/riscv/bitmanip.md
@@ -595,3 +595,45 @@
 	operands[3] = GEN_INT (bits | topbit);
 	operands[4] = GEN_INT (~topbit);
 })
+
+;; IF_THEN_ELSE: test for 2 bits of opposite polarity
+(define_insn_and_split "*branch<X:mode>_mask_twobits_equals_singlebit"
+  [(set (pc)
+	(if_then_else
+	  (match_operator 1 "equality_operator"
+	    [(and:X (match_operand:X 2 "register_operand" "r")
+		    (match_operand:X 3 "const_twobits_not_arith_operand" "i"))
+	     (match_operand:X 4 "single_bit_mask_operand" "i")])
+	 (label_ref (match_operand 0 "" ""))
+	 (pc)))
+   (clobber (match_scratch:X 5 "=&r"))
+   (clobber (match_scratch:X 6 "=&r"))]
+  "TARGET_ZBS && TARGET_ZBB"
+  "#"
+  "&& reload_completed"
+  [(set (match_dup 5) (zero_extract:X (match_dup 2)
+				      (const_int 1)
+				      (match_dup 8)))
+   (set (match_dup 6) (zero_extract:X (match_dup 2)
+				      (const_int 1)
+				      (match_dup 9)))
+   (set (match_dup 6) (and:X (not:X (match_dup 6)) (match_dup 5)))
+   (set (pc) (if_then_else (match_op_dup 1 [(match_dup 6) (const_int 0)])
+			   (label_ref (match_dup 0))
+			   (pc)))]
+{
+   unsigned HOST_WIDE_INT twobits_mask = UINTVAL (operands[3]);
+   unsigned HOST_WIDE_INT singlebit_mask = UINTVAL (operands[4]);
+
+   /* We should never see an unsatisfiable condition.  */
+   gcc_assert (twobits_mask & singlebit_mask);
+
+   int setbit = ctz_hwi (singlebit_mask);
+   int clearbit = ctz_hwi (twobits_mask & ~singlebit_mask);
+
+   operands[1] = gen_rtx_fmt_ee (GET_CODE (operands[1]) == NE ? EQ : NE,
+				 <X:MODE>mode, operands[6], GEN_INT(0));
+
+   operands[8] = GEN_INT (setbit);
+   operands[9] = GEN_INT (clearbit);
+})
diff --git a/gcc/config/riscv/predicates.md b/gcc/config/riscv/predicates.md
index 9976b50..dfd9876 100644
--- a/gcc/config/riscv/predicates.md
+++ b/gcc/config/riscv/predicates.md
@@ -310,6 +310,11 @@
   (and (match_code "const_int")
        (match_test "popcount_hwi (UINTVAL (op)) == 2")))
 
+(define_predicate "const_twobits_not_arith_operand"
+  (and (match_code "const_int")
+       (and (not (match_operand 0 "arith_operand"))
+	    (match_operand 0 "const_twobits_operand"))))
+
 ;; A CONST_INT operand that fits into the unsigned half of a
 ;; signed-immediate after the top bit has been cleared
 (define_predicate "uimm_extra_bit_operand"
diff --git a/gcc/testsuite/gcc.target/riscv/zbs-if_then_else-01.c b/gcc/testsuite/gcc.target/riscv/zbs-if_then_else-01.c
new file mode 100644
index 0000000..d249a84
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/zbs-if_then_else-01.c
@@ -0,0 +1,20 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gc_zbb_zbs -mabi=lp64" } */
+/* { dg-skip-if "" { *-*-* } { "-O0" "-Og" "-O1" } } */
+
+void g();
+
+void f1 (long a)
+{
+  if ((a & ((1ul << 33) | (1 << 4))) == (1ul << 33))
+    g();
+}
+
+void f2 (long a)
+{
+  if ((a & 0x12) == 0x10)
+    g();
+}
+
+/* { dg-final { scan-assembler-times "bexti\t" 2 } } */
+/* { dg-final { scan-assembler-times "andn\t" 1 } } */