Introduce repeat_operation

This adds class repeat_operation, which implements BINOP_REPEAT.

gdb/ChangeLog
2021-03-08  Tom Tromey  <tom@tromey.com>

	* expop.h (class repeat_operation): New.
	* eval.c (eval_op_repeat): No longer static.  Remove "op"
	parameter.
	(evaluate_subexp_standard): Update.
	* ax-gdb.c (repeat_operation::do_generate_ax): New method.

gdb/ChangeLog

@@ -1,3 +1,11 @@
+2021-03-08  Tom Tromey  <tom@tromey.com>
+
+	* expop.h (class repeat_operation): New.
+	* eval.c (eval_op_repeat): No longer static.  Remove "op"
+	parameter.
+	(evaluate_subexp_standard): Update.
+	* ax-gdb.c (repeat_operation::do_generate_ax): New method.
+
 2021-03-08  Tom Tromey  <tom@tromey.com>
 
 	* expop.h (class comparison_operation): New.

gdb/ax-gdb.c

@@ -2419,6 +2419,56 @@ ternop_cond_operation::do_generate_ax (struct expression *exp,
   value->kind = value2.kind;
 }
 
+/* Generate code for GDB's magical `repeat' operator.
+   LVALUE @ INT creates an array INT elements long, and whose elements
+   have the same type as LVALUE, located in memory so that LVALUE is
+   its first element.  For example, argv[0]@argc gives you the array
+   of command-line arguments.
+
+   Unfortunately, because we have to know the types before we actually
+   have a value for the expression, we can't implement this perfectly
+   without changing the type system, having values that occupy two
+   stack slots, doing weird things with sizeof, etc.  So we require
+   the right operand to be a constant expression.  */
+void
+repeat_operation::do_generate_ax (struct expression *exp,
+				  struct agent_expr *ax,
+				  struct axs_value *value,
+				  struct type *cast_type)
+{
+  struct axs_value value1;
+
+  /* We don't want to turn this into an rvalue, so no conversions
+     here.  */
+  std::get<0> (m_storage)->generate_ax (exp, ax, &value1);
+  if (value1.kind != axs_lvalue_memory)
+    error (_("Left operand of `@' must be an object in memory."));
+
+  /* Evaluate the length; it had better be a constant.  */
+  if (!std::get<1> (m_storage)->constant_p ())
+    error (_("Right operand of `@' must be a "
+	     "constant, in agent expressions."));
+
+  struct value *v
+    = std::get<1> (m_storage)->evaluate (nullptr, exp,
+					 EVAL_AVOID_SIDE_EFFECTS);
+  if (value_type (v)->code () != TYPE_CODE_INT)
+    error (_("Right operand of `@' must be an integer."));
+  int length = value_as_long (v);
+  if (length <= 0)
+    error (_("Right operand of `@' must be positive."));
+
+  /* The top of the stack is already the address of the object, so
+     all we need to do is frob the type of the lvalue.  */
+  /* FIXME-type-allocation: need a way to free this type when we are
+     done with it.  */
+  struct type *array
+    = lookup_array_range_type (value1.type, 0, length - 1);
+
+  value->kind = axs_lvalue_memory;
+  value->type = array;
+}
+
 }
 
 /* This handles the middle-to-right-side of code generation for binary

gdb/eval.c

@@ -1732,9 +1732,9 @@ eval_op_leq (struct type *expect_type, struct expression *exp,
 
 /* A helper function for BINOP_REPEAT.  */
 
-static struct value *
+struct value *
 eval_op_repeat (struct type *expect_type, struct expression *exp,
-		enum noside noside,
+		enum noside noside, enum exp_opcode op,
 		struct value *arg1, struct value *arg2)
 {
   if (noside == EVAL_SKIP)
@@ -2946,7 +2946,7 @@ evaluate_subexp_standard (struct type *expect_type,
     case BINOP_REPEAT:
       arg1 = evaluate_subexp (nullptr, exp, pos, noside);
       arg2 = evaluate_subexp (nullptr, exp, pos, noside);
-      return eval_op_repeat (expect_type, exp, noside, arg1, arg2);
+      return eval_op_repeat (expect_type, exp, noside, op, arg1, arg2);
 
     case BINOP_COMMA:
       evaluate_subexp (nullptr, exp, pos, noside);

gdb/expop.h

@@ -135,6 +135,11 @@ extern struct value *eval_op_leq (struct type *expect_type,
 				  enum noside noside, enum exp_opcode op,
 				  struct value *arg1,
 				  struct value *arg2);
+extern struct value *eval_op_repeat (struct type *expect_type,
+				     struct expression *exp,
+				     enum noside noside, enum exp_opcode op,
+				     struct value *arg1,
+				     struct value *arg2);
 
 namespace expr
 {
@@ -1188,6 +1193,21 @@ using gtr_operation = comparison_operation<BINOP_GTR, eval_op_gtr>;
 using geq_operation = comparison_operation<BINOP_GEQ, eval_op_geq>;
 using leq_operation = comparison_operation<BINOP_LEQ, eval_op_leq>;
 
+/* Implement the GDB '@' repeat operator.  */
+class repeat_operation
+  : public binop_operation<BINOP_REPEAT, eval_op_repeat>
+{
+  using binop_operation<BINOP_REPEAT, eval_op_repeat>::binop_operation;
+
+protected:
+
+  void do_generate_ax (struct expression *exp,
+		       struct agent_expr *ax,
+		       struct axs_value *value,
+		       struct type *cast_type)
+    override;
+};
+
 } /* namespace expr */
 
 #endif /* EXPOP_H */