RISC-V: Optimize branches testing a bit-range or a shifted immediate

gcc/ChangeLog:

	* config/riscv/predicates.md (shifted_const_arith_operand): New predicate.
	(uimm_extra_bit_operand): New predicate.
	* config/riscv/riscv.md (*branch<ANYI:mode>_shiftedarith_equals_zero):
	New pattern.
	(*branch<ANYI:mode>_shiftedmask_equals_zero): New pattern.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/branch-1.c: New test.

gcc/config/riscv/predicates.md

@@ -290,3 +290,26 @@
 (define_predicate "const_nottwobits_operand"
   (and (match_code "const_int")
        (match_test "popcount_hwi (~UINTVAL (op)) == 2")))
+
+;; A CONST_INT operand that consists of a single run of 32 consecutive
+;; set bits.
+(define_predicate "consecutive_bits32_operand"
+  (and (match_operand 0 "consecutive_bits_operand")
+       (match_test "popcount_hwi (UINTVAL (op)) == 32")))
+
+;; A CONST_INT operand that, if shifted down to start with its least
+;; significant non-zero bit, is a SMALL_OPERAND (suitable as an
+;; immediate to logical and arithmetic instructions).
+(define_predicate "shifted_const_arith_operand"
+  (and (match_code "const_int")
+       (match_test "ctz_hwi (INTVAL (op)) > 0")
+       (match_test "SMALL_OPERAND (INTVAL (op) >> ctz_hwi (INTVAL (op)))")))
+
+;; 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"
+  (and (match_code "const_int")
+       (not (and (match_test "SMALL_OPERAND (INTVAL (op))")
+		 (match_test "INTVAL (op) > 0")))
+       (ior (match_test "SMALL_OPERAND (UINTVAL (op) & ~(HOST_WIDE_INT_1U << floor_log2 (UINTVAL (op))))")
+	    (match_test "popcount_hwi (UINTVAL (op)) == 2"))))

gcc/config/riscv/riscv.md

@@ -2216,6 +2216,57 @@
 
 ;; Conditional branches
 
+(define_insn_and_split "*branch<ANYI:mode>_shiftedarith_equals_zero"
+  [(set (pc)
+	(if_then_else (match_operator 1 "equality_operator"
+		       [(and:ANYI (match_operand:ANYI 2 "register_operand" "r")
+				  (match_operand 3 "shifted_const_arith_operand" "i"))
+			(const_int 0)])
+	 (label_ref (match_operand 0 "" ""))
+	 (pc)))
+   (clobber (match_scratch:ANYI 4 "=&r"))]
+  "INTVAL (operands[3]) >= 0 || !partial_subreg_p (operands[2])"
+  "#"
+  "&& reload_completed"
+  [(set (match_dup 4) (lshiftrt:ANYI (match_dup 2) (match_dup 6)))
+   (set (match_dup 4) (and:ANYI (match_dup 4) (match_dup 7)))
+   (set (pc) (if_then_else (match_op_dup 1 [(match_dup 4) (const_int 0)])
+			   (label_ref (match_dup 0)) (pc)))]
+{
+	HOST_WIDE_INT mask = INTVAL (operands[3]);
+	int trailing = ctz_hwi (mask);
+
+	operands[6] = GEN_INT (trailing);
+	operands[7] = GEN_INT (mask >> trailing);
+})
+
+(define_insn_and_split "*branch<ANYI:mode>_shiftedmask_equals_zero"
+  [(set (pc)
+	(if_then_else (match_operator 1 "equality_operator"
+		       [(and:ANYI (match_operand:ANYI 2 "register_operand" "r")
+				  (match_operand 3 "consecutive_bits_operand" "i"))
+			(const_int 0)])
+	 (label_ref (match_operand 0 "" ""))
+	 (pc)))
+   (clobber (match_scratch:X 4 "=&r"))]
+  "(INTVAL (operands[3]) >= 0 || !partial_subreg_p (operands[2]))
+    && popcount_hwi (INTVAL (operands[3])) > 1
+    && !SMALL_OPERAND (INTVAL (operands[3]))"
+  "#"
+  "&& reload_completed"
+  [(set (match_dup 4) (ashift:X (subreg:X (match_dup 2) 0) (match_dup 6)))
+   (set (match_dup 4) (lshiftrt:X (match_dup 4) (match_dup 7)))
+   (set (pc) (if_then_else (match_op_dup 1 [(match_dup 4) (const_int 0)])
+			   (label_ref (match_dup 0)) (pc)))]
+{
+	unsigned HOST_WIDE_INT mask = INTVAL (operands[3]);
+	int leading  = clz_hwi (mask);
+	int trailing = ctz_hwi (mask);
+
+	operands[6] = GEN_INT (leading);
+	operands[7] = GEN_INT (leading + trailing);
+})
+
 (define_insn "*branch<mode>"
   [(set (pc)
 	(if_then_else

gcc/testsuite/gcc.target/riscv/branch-1.c

@@ -0,0 +1,37 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gc -mabi=lp64" } */
+/* { dg-skip-if "" { *-*-* } { "-O0" "-Og" "-O1" } } */
+
+void g();
+
+void f(long long a) 
+{
+  if (a & 0xff00)
+    g();
+}
+
+void f2(long long a) 
+{
+  if (a & (-4ull << 3))
+    g();
+}
+
+void f3(long long a) 
+{
+  if (a & 0xffff00)
+    g();
+}
+
+void f4(long long a)
+{
+  if (a & 0x7ff800)
+    g();
+}
+
+/* { dg-final { scan-assembler-times "slli\t" 2 } } */
+/* { dg-final { scan-assembler-times "srli\t" 3 } } */
+/* { dg-final { scan-assembler-times "andi\t" 1 } } */
+/* { dg-final { scan-assembler-times "\tli\t" 1 } } */
+/* { dg-final { scan-assembler-not "addi\t" } } */
+/* { dg-final { scan-assembler-not "and\t" } } */
+