RISC-V: Produce better code with complex constants [PR95632] [PR106602]

gcc/Changelog:
	PR target/95632
	PR target/106602
	* config/riscv/riscv.md: New pattern to simulate complex
	const_int loads.

gcc/testsuite/ChangeLog:
	* gcc.target/riscv/pr95632.c: New test.
	* gcc.target/riscv/pr106602.c: New test.

gcc/config/riscv/riscv.md

@@ -1670,6 +1670,23 @@
 		      MAX_MACHINE_MODE, &operands[3], TRUE);
 })
 
+;; Pretend to have the ability to load complex const_int in order to get
+;; better code generation around them.
+;;
+;; But avoid constants that are special cased elsewhere.
+(define_insn_and_split "*mvconst_internal"
+  [(set (match_operand:GPR 0 "register_operand" "=r")
+        (match_operand:GPR 1 "splittable_const_int_operand" "i"))]
+  "!(p2m1_shift_operand (operands[1]) || high_mask_shift_operand (operands[1]))"
+  "#"
+  "&& 1"
+  [(const_int 0)]
+{
+  riscv_move_integer (operands[0], operands[0], INTVAL (operands[1]),
+                      <MODE>mode, TRUE);
+  DONE;
+})
+
 ;; 64-bit integer moves
 
 (define_expand "movdi"

gcc/testsuite/gcc.target/riscv/pr106602.c

@@ -0,0 +1,14 @@
+/* { dg-do compile { target { riscv64*-*-* } } } */
+/* { dg-options "-O2" } */
+
+unsigned long
+foo2 (unsigned long a)
+{
+  return (unsigned long)(unsigned int) a << 6;
+}
+
+/* { dg-final { scan-assembler-times "slli\t" 1 } } */
+/* { dg-final { scan-assembler-times "srli\t" 1 } } */
+/* { dg-final { scan-assembler-not "\tli\t" } } */
+/* { dg-final { scan-assembler-not "addi\t" } } */
+/* { dg-final { scan-assembler-not "and\t" } } */

gcc/testsuite/gcc.target/riscv/pr95632.c

@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+unsigned short
+foo (unsigned short crc)
+{
+  crc ^= 0x4002;
+  crc >>= 1;
+  crc |= 0x8000;
+
+  return crc;
+}
+
+/* { dg-final { scan-assembler-times "srli\t" 1 } } */
+/* { dg-final { scan-assembler-not "slli\t" } } */