RISC-V: Fix ICE in branch<ANYI:mode>_shiftedarith_equals_zero

With the recent improvements to the splitting of special cases of
branch patterns on RISC-V, a dependency on an unmerged/in-discussion
change for branch-equals-zero slipped in: this allowed a non-X mode to
be presented to branch-equals-zero (where only X mode is permissible).

This addresses the issue by wrapping the ANYI operand in a paradoxical
SUBREG:X (the high bits can be safely ignored, as we we perform an
and-immediate before the branch in the pattern).

Tested against the GCC testsuite and committed as obvious.

gcc/ChangeLog:

	PR target/107786
	* config/riscv/riscv.md
	(*branch<ANYI:mode>_shiftedarith_equals_zero): Wrap ANYI
	in a subreg, as our branch instructions only supports X.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/pr107786-2.c: New test.
	* gcc.target/riscv/pr107786.c: New test.

gcc/config/riscv/riscv.md

@@ -2224,12 +2224,12 @@
 			(const_int 0)])
 	 (label_ref (match_operand 0 "" ""))
 	 (pc)))
-   (clobber (match_scratch:ANYI 4 "=&r"))]
-  "INTVAL (operands[3]) >= 0 || !partial_subreg_p (operands[2])"
+   (clobber (match_scratch:X 4 "=&r"))]
+  "!SMALL_OPERAND (INTVAL (operands[3]))"
   "#"
   "&& 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 (match_dup 4) (lshiftrt:X (subreg:X (match_dup 2) 0) (match_dup 6)))
+   (set (match_dup 4) (and: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)))]
 {

gcc/testsuite/gcc.target/riscv/pr107786-2.c

@@ -0,0 +1,17 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gc -mabi=lp64" } */
+/* { dg-skip-if "" { *-*-* } { "-O0" "-Og" "-O1" } } */
+
+int c;
+
+int main() {
+  for (;;) {
+    short h = c * 100;
+    if (h & 0x7ff0)
+      break;
+  }
+}
+
+/* { dg-final { scan-assembler-times "andi\t" 1 } } */
+/* { dg-final { scan-assembler-times "srli\t" 1 } } */
+

gcc/testsuite/gcc.target/riscv/pr107786.c

@@ -0,0 +1,17 @@
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gc -mabi=lp64" } */
+/* { dg-skip-if "" { *-*-* } { "-O0" "-Og" "-O1" } } */
+
+int c;
+
+int main() {
+  for (;;) {
+    char h = c * 100;
+    if (h)
+      break;
+  }
+}
+
+/* { dg-final { scan-assembler-times "andi\t" 1 } } */
+/* { dg-final { scan-assembler-not "srli\t" } } */
+