Add an expr::operation_up to struct expression

This adds an expr::operation_up to struct expression, and then
modifies various parts of GDB to use this member when it is non-null.
The list of such spots was a bit surprising to me, and found only
after writing most of the code and then noticing what no longer
compiled.

In a few spots, new accessor methods are added to operation
subclasses, so that code that dissects an expression will work with
the new scheme.

After this change, code that constructs an expression can be switched
to the new form without breaking.

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

	* ada-exp.h (class ada_var_value_operation) <get_symbol>: Remove;
	now in superclass.
	* value.h (fetch_subexp_value): Add "op" parameter.
	* value.c (init_if_undefined_command): Update.
	* tracepoint.c (validate_actionline, encode_actions_1): Update.
	* stap-probe.c (stap_probe::compile_to_ax): Update.
	* printcmd.c (set_command): Update.
	* ppc-linux-nat.c (ppc_linux_nat_target::check_condition):
	Update.
	* parser-defs.h (struct expr_builder) <set_operation>: New
	method.
	* parse.c (parse_exp_in_context, exp_uses_objfile): Update.
	* expression.h (struct expression) <first_opcode>: Update.
	<op>: New member.
	* expprint.c (dump_raw_expression, dump_prefix_expression):
	Update.
	* expop.h (class var_value_operation) <get_symbol>: New method.
	(class register_operation) <get_name>: New method.
	(class equal_operation): No longer a typedef, now a subclass.
	(class unop_memval_operation) <get_type>: New method.
	(class assign_operation) <get_lhs>: New method.
	(class unop_cast_operation) <get_type>: New method.
	* eval.c (evaluate_expression, evaluate_type)
	(evaluate_subexpression_type): Update.
	(fetch_subexp_value): Add "op" parameter.
	(parse_and_eval_type): Update.
	* dtrace-probe.c (dtrace_probe::compile_to_ax): Update.
	* breakpoint.c (update_watchpoint, watchpoint_check)
	(watchpoint_exp_is_const, watch_command_1): Update.
	* ax-gdb.c (gen_trace_for_expr, gen_eval_for_expr, gen_printf):
	Update.

1 files changed, 4 insertions, 1 deletions

diff --git a/gdb/expression.h b/gdb/expression.h
index d20857bf268..3abaf6e6dc7 100644
--- a/gdb/expression.h
+++ b/gdb/expression.h
@@ -240,7 +240,9 @@ struct expression
      expression.  */
   enum exp_opcode first_opcode () const
   {
-      return elts[0].opcode;
+    if (op != nullptr)
+      return op->opcode ();
+    return elts[0].opcode;
   }
 
   /* Evaluate the expression.  EXPECT_TYPE is the context type of the
@@ -252,6 +254,7 @@ struct expression
   const struct language_defn *language_defn;
   /* Architecture it was parsed in.  */
   struct gdbarch *gdbarch;
+  expr::operation_up op;
   int nelts = 0;
   union exp_element *elts;
 };