RISC-V: Bugfix for scalar move with merged operand

Given below example for VLS mode

void
test (vl_t *u)
{
  vl_t t;
  long long *p = (long long *)&t;

  p[0] = p[1] = 2;

  *u = t;
}

The vec_set will simplify the insn to vmv.s.x when index is 0, without
merged operand. That will result in some problems in DCE, aka:

1:  137[DI] = a0
2:  138[V2DI] = 134[V2DI]                              // deleted by DCE
3:  139[DI] = #2                                       // deleted by DCE
4:  140[DI] = #2                                       // deleted by DCE
5:  141[V2DI] = vec_dup:V2DI (139[DI])                 // deleted by DCE
6:  138[V2DI] = vslideup_imm (138[V2DI], 141[V2DI], 1) // deleted by DCE
7:  135[V2DI] = 138[V2DI]                              // deleted by DCE
8:  142[V2DI] = 135[V2DI]                              // deleted by DCE
9:  143[DI] = #2
10: 142[V2DI] = vec_dup:V2DI (143[DI])
11: (137[DI]) = 142[V2DI]

The higher 64 bits of 142[V2DI] is unknown here and it generated incorrect
code when store back to memory. This patch would like to fix this issue
by adding a new SCALAR_MOVE_MERGED_OP for vec_set.

Please note this patch doesn't enable VLS for vec_set, the underlying
patches will support this soon.

gcc/ChangeLog:

	* config/riscv/autovec.md: Bugfix.
	* config/riscv/riscv-protos.h (SCALAR_MOVE_MERGED_OP): New enum.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/base/scalar-move-merged-run-1.c: New test.

Signed-off-by: Pan Li <pan2.li@intel.com>

gcc/config/riscv/autovec.md

@@ -1401,9 +1401,9 @@
   /* If we set the first element, emit an v(f)mv.s.[xf].  */
   if (operands[2] == const0_rtx)
     {
-      rtx ops[] = {operands[0], operands[1]};
+      rtx ops[] = {operands[0], operands[0], operands[1]};
       riscv_vector::emit_nonvlmax_insn (code_for_pred_broadcast (<MODE>mode),
-                                         riscv_vector::SCALAR_MOVE_OP, ops, CONST1_RTX (Pmode));
+					riscv_vector::SCALAR_MOVE_MERGED_OP, ops, CONST1_RTX (Pmode));
     }
   else
     {

gcc/config/riscv/riscv-protos.h

@@ -345,6 +345,10 @@ enum insn_type : unsigned int
   SCALAR_MOVE_OP = HAS_DEST_P | HAS_MASK_P | USE_ONE_TRUE_MASK_P | HAS_MERGE_P
 		   | USE_VUNDEF_MERGE_P | TDEFAULT_POLICY_P | MDEFAULT_POLICY_P
 		   | UNARY_OP_P,
+
+  SCALAR_MOVE_MERGED_OP = HAS_DEST_P | HAS_MASK_P | USE_ONE_TRUE_MASK_P
+			  | HAS_MERGE_P | TDEFAULT_POLICY_P | MDEFAULT_POLICY_P
+			  | UNARY_OP_P,
 };
 
 enum vlmul_type

gcc/testsuite/gcc.target/riscv/rvv/base/scalar-move-merged-run-1.c

@@ -0,0 +1,29 @@
+/* { dg-do run { target { riscv_vector } } } */
+/* { dg-options "-O3 -Wno-psabi" } */
+
+#define TEST_VAL 2
+
+typedef long long vl_t __attribute__((vector_size(2 * sizeof (long long))));
+
+void init_vl (vl_t *u)
+{
+  vl_t t;
+  long long *p = (long long *)&t;
+
+  p[0] = p[1] = TEST_VAL;
+
+  *u = t;
+}
+
+int
+main ()
+{
+  vl_t vl = {};
+
+  init_vl (&vl);
+
+  if (vl[0] != TEST_VAL || vl[1] != TEST_VAL)
+    __builtin_abort ();
+
+  return 0;
+}