Handle null objects in general.

.gitignore

@@ -13,6 +13,7 @@ tags
 TAGS
 cscope.*
 *.patch
+*.orig
 
 # Object files and libraries
 *.[oa]

PExpr.h

@@ -494,6 +494,8 @@ class PENull : public PExpr {
       virtual void dump(ostream&) const;
       virtual unsigned test_width(Design*des, NetScope*scope,
 				  width_mode_t&mode);
+      virtual NetExpr*elaborate_expr(Design*des, NetScope*scope,
+				     ivl_type_t type, unsigned flags) const;
       virtual NetExpr*elaborate_expr(Design*des, NetScope*,
 				     unsigned expr_wid,
                                      unsigned flags) const;

elab_expr.cc

@@ -4015,8 +4015,7 @@ NetExpr* PENew::elaborate_expr(Design*des, NetScope*scope,
 /*
  * This method should never actually be called.
  */
-NetExpr* PENew::elaborate_expr(Design*des, NetScope*scope,
-				 unsigned, unsigned flags) const
+NetExpr* PENew::elaborate_expr(Design*, NetScope*, unsigned, unsigned) const
 {
       ivl_assert(*this, 0);
       return 0;
@@ -4053,6 +4052,13 @@ unsigned PENull::test_width(Design*, NetScope*, width_mode_t&)
       return expr_width_;
 }
 
+NetExpr* PENull::elaborate_expr(Design*, NetScope*, ivl_type_t, unsigned) const
+{
+      NetENull*tmp = new NetENull;
+      tmp->set_line(*this);
+      return tmp;
+}
+
 NetExpr* PENull::elaborate_expr(Design*, NetScope*, unsigned, unsigned) const
 {
       NetENull*tmp = new NetENull;

elaborate.cc

@@ -2385,6 +2385,9 @@ NetProc* PAssign::elaborate(Design*des, NetScope*scope) const
 		 handle it with this code instead. */
 	    rv = elaborate_rval_(des, scope, lv->sig()->net_type());
 
+      } else if (lv->more==0 && dynamic_cast<const PENull*> (rval())) {
+	    rv = elaborate_rval_(des, scope, lv->sig()->net_type());
+
       } else if (lv->more==0 && dynamic_cast<const PENewClass*> (rval())) {
 
 	    rv = elaborate_rval_(des, scope, lv->sig()->net_type());

tgt-vvp/eval_object.c

@@ -73,6 +73,12 @@ static int eval_class_new(ivl_expr_t ex)
       return 0;
 }
 
+static int eval_object_null(ivl_expr_t ex)
+{
+      fprintf(vvp_out, "    %%null;\n");
+      return 0;
+}
+
 int draw_eval_object(ivl_expr_t ex)
 {
       switch (ivl_expr_type(ex)) {
@@ -88,6 +94,10 @@ int draw_eval_object(ivl_expr_t ex)
 			  ivl_expr_value(ex));
 		  return 0;
 	    }
+
+	  case IVL_EX_NULL:
+	    return eval_object_null(ex);
+
 	  default:
 	    fprintf(vvp_out, "; ERROR: Invalid expression type %u\n", ivl_expr_type(ex));
 	    return 1;

vvp/codes.h

@@ -153,6 +153,7 @@ extern bool of_NEW_DARRAY(vthread_t thr, vvp_code_t code);
 extern bool of_NOOP(vthread_t thr, vvp_code_t code);
 extern bool of_NOR(vthread_t thr, vvp_code_t code);
 extern bool of_NORR(vthread_t thr, vvp_code_t code);
+extern bool of_NULL(vthread_t thr, vvp_code_t code);
 extern bool of_OR(vthread_t thr, vvp_code_t code);
 extern bool of_ORR(vthread_t thr, vvp_code_t code);
 extern bool of_PAD(vthread_t thr, vvp_code_t code);

vvp/compile.cc

@@ -201,6 +201,7 @@ static const struct opcode_table_s opcode_table[] = {
       { "%noop",   of_NOOP,   0,  {OA_NONE,     OA_NONE,     OA_NONE} },
       { "%nor",    of_NOR,    3,  {OA_BIT1,     OA_BIT2,     OA_NUMBER} },
       { "%nor/r",  of_NORR,   3,  {OA_BIT1,     OA_BIT2,     OA_NUMBER} },
+      { "%null",   of_NULL,   0,  {OA_NONE,     OA_NONE,     OA_NONE} },
       { "%or",     of_OR,     3,  {OA_BIT1,     OA_BIT2,     OA_NUMBER} },
       { "%or/r",   of_ORR,    3,  {OA_BIT1,     OA_BIT2,     OA_NUMBER} },
       { "%pad",    of_PAD,    3,  {OA_BIT1,     OA_BIT2,     OA_NUMBER} },

vvp/opcodes.txt

@@ -386,7 +386,14 @@ supports run-time calculated delays.
 * %delete/obj <var-label>
 
 Arrange for the dynamic object at the target label to be deleted.
-This has no effect on the object or string stack.
+This has no effect on the object or string stack. Note that this is
+the same as:
+
+   %null ;
+   %store/obj <var-label>
+
+but that idiom is expected to be common enough that it warrants an
+optimized shorthand.
 
 * %disable <scope-label>
 
@@ -802,6 +809,11 @@ The actual operation performed is the inverted or of all the bits in
 the vector.
 
 
+* %null
+
+Push a null object and push it to the object stack. The null object
+can be used with any class or darray object, so it is not typed.
+
 * %or <dst>, <src>, <wid>
 
 Perform the bitwise or of the vectors. Each bit in the <dst> is

vvp/vthread.cc

@@ -4146,6 +4146,17 @@ bool of_NORR(vthread_t thr, vvp_code_t cp)
       return true;
 }
 
+/*
+ * Push a null to the object stack.
+ */
+bool of_NULL(vthread_t thr, vvp_code_t cp)
+{
+      vvp_object_t tmp;
+      thr->push_object(tmp);
+      return true;
+}
+
+
 bool of_ANDR(vthread_t thr, vvp_code_t cp)
 {
       assert(cp->bit_idx[0] >= 4);