[qfcc] Create a nil operand

This is for struct assignments so they can pass the source operand back
up the assignment chain.

tools/qfcc/include/statements.h

@@ -38,6 +38,7 @@ typedef enum {
 	op_label,
 	op_temp,
 	op_alias,
+	op_nil,
 } op_type_e;
 
 typedef struct {
@@ -55,7 +56,7 @@ typedef struct {
 typedef struct operand_s {
 	struct operand_s *next;
 	op_type_e   op_type;
-	struct type_s *type;		///< possibly override def's type
+	struct type_s *type;		///< possibly override def's/nil's type
 	int         size;			///< for structures
 	struct expr_s *expr;		///< expression generating this operand
 	void       *return_addr;	///< who created this operand
@@ -117,6 +118,7 @@ struct dstring_s;
 
 const char *optype_str (op_type_e type) __attribute__((const));
 
+operand_t *nil_operand (struct type_s *type, struct expr_s *expr);
 operand_t *def_operand (struct def_s *def, struct type_s *type,
 						struct expr_s *expr);
 operand_t *return_operand (struct type_s *type, struct expr_s *expr);

tools/qfcc/source/emit.c

@@ -106,6 +106,8 @@ get_operand_def (expr_t *expr, operand_t *op)
 			return op->o.tempop.def;
 		case op_alias:
 			return get_operand_def (expr, op->o.alias);
+		case op_nil:
+			internal_error (expr, "unexpected nil operand");
 	}
 	return 0;
 }

tools/qfcc/source/flow.c

@@ -281,6 +281,8 @@ flowvar_get_def (flowvar_t *var)
 			return op->o.tempop.def;
 		case op_alias:
 			internal_error (op->expr, "unexpected alias operand");
+		case op_nil:
+			internal_error (op->expr, "unexpected nil operand");
 	}
 	internal_error (op->expr, "oops, blue pill");
 	return 0;

tools/qfcc/source/statements.c

@@ -65,6 +65,8 @@ static const char *op_type_names[] = {
 	"op_value",
 	"op_label",
 	"op_temp",
+	"op_alias",
+	"op_nil",
 };
 
 const char *
@@ -150,6 +152,8 @@ operand_string (operand_t *op)
 				strcpy (buf, alias);
 				return va ("alias(%s,%s)", pr_type_name[op->type->type], buf);
 			}
+		case op_nil:
+			return va ("nil");
 	}
 	return ("??");
 }
@@ -222,6 +226,10 @@ print_operand (operand_t *op)
 			printf ("alias(%s,", pr_type_name[op->type->type]);
 			print_operand (op->o.alias);
 			printf (")");
+			break;
+		case op_nil:
+			printf ("nil");
+			break;
 	}
 }
 
@@ -313,6 +321,16 @@ free_sblock (sblock_t *sblock)
 	FREE (sblocks, sblock);
 }
 
+operand_t *
+nil_operand (type_t *type, expr_t *expr)
+{
+	operand_t  *op;
+	op = new_operand (op_nil, expr, __builtin_return_address (0));
+	op->type = type;
+	op->size = type_size (type);
+	return op;
+}
+
 operand_t *
 def_operand (def_t *def, type_t *type, expr_t *expr)
 {