[xstormy16] Efficient HImode rotate left by a single bit.

This patch contains some minor tweak to xstormy16's machine description
most significantly providing a pattern for HImode rotate left by a single
bit that requires only two instructions.

unsigned short foo(unsigned short x)
{
  return (x << 1) | (x >> 15);
}

currently with -O2 generates:
foo:    mov r7,r2
        shr r7,#15
        shl r2,#1
        or r2,r7
        ret

with this patch, GCC now generates:
foo:	shl r2,#1 | adc r2,#0
        ret

Additionally neghi2 is converted to a define_insn (so that the RTL
optimizers see the negation semantics), and HImode rotations by
8-bits can now be recognized and implemented using swpb.

2023-04-29  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	* config/stormy16/stormy16.md (neghi2): Convert from a define_expand
	to a define_insn.
	(*rotatehi_1): New define_insn for efficient 2 insn sequence.
	(*rotatehi_8, *rotaterthi_8): New define_insn to emit a swpb.

gcc/testsuite/ChangeLog
	* gcc.target/xstormy16/neghi2.c: New test case.
	* gcc.target/xstormy16/rotatehi-1.c: Likewise.

gcc/config/stormy16/stormy16.md

@@ -518,13 +518,13 @@
 
 ;; Negation
 
-(define_expand "neghi2"
-  [(set (match_operand:HI 0 "register_operand" "")
-	(not:HI (match_operand:HI 1 "register_operand" "")))
-   (parallel [(set (match_dup 0) (plus:HI (match_dup 0) (const_int 1)))
+(define_insn "neghi2"
+  [(parallel [(set (match_operand:HI 0 "register_operand" "=r")
+		   (neg:HI (match_operand:HI 1 "register_operand" "0")))
 	      (clobber (reg:BI CARRY_REG))])]
   ""
-  "")
+  "not %0 | add %0,#1"
+  [(set_attr "length" "4")])
 
 ;; ::::::::::::::::::::
 ;; ::
@@ -558,6 +558,24 @@
    (clobber (reg:BI CARRY_REG))]
   ""
   "shr %0,%2")
+
+;; HImode rotate left by 1 bit
+(define_insn "*rotatehi_1"
+  [(set (match_operand:HI 0 "register_operand" "=r")
+	(rotate:HI (match_operand:HI 1 "register_operand" "0")
+		   (const_int 1)))
+   (clobber (reg:BI CARRY_REG))]
+  ""
+  "shl %0,#1 | adc %0,#0"
+  [(set_attr "length" "4")])
+
+;; HImode rotate left by 8 bits
+(define_insn "*<code>hi_8"
+  [(set (match_operand:HI 0 "register_operand" "=r")
+	(any_rotate:HI (match_operand:HI 1 "register_operand" "0")
+		       (const_int 8)))]
+  ""
+  "swpb %0")
 
 ;; ::::::::::::::::::::
 ;; ::

gcc/testsuite/gcc.target/xstormy16/neghi2.c

@@ -0,0 +1,8 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+short neg(short x)
+{
+  return -x;
+}
+/* { dg-final { scan-assembler "not r2 | add r2,#1" } } */

gcc/testsuite/gcc.target/xstormy16/rotatehi-1.c

@@ -0,0 +1,10 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+unsigned short foo(unsigned short x)
+{
+  return (x << 1) | (x >> 15);
+}
+
+/* { dg-final { scan-assembler "shl r2,#1" } } */
+/* { dg-final { scan-assembler "adc r2,#0" } } */