Introduce expression::first_opcode

This adds a new helper method, expression::first_opcode, that extracts
the outermost opcode of an expression.  This simplifies some patches
in the expression rewrite series.

Note that this patch requires the earlier patch to avoid manual
dissection of OP_TYPE operations.

2020-12-15  Tom Tromey  <tom@tromey.com>

	* varobj.c (varobj_create): Use first_opcode.
	* value.c (init_if_undefined_command): Use first_opcode.
	* typeprint.c (whatis_exp): Use first_opcode.
	* tracepoint.c (validate_actionline): Use first_opcode.
	(encode_actions_1): Use first_opcode.
	* stack.c (return_command): Use first_opcode.
	* expression.h (struct expression) <first_opcode>: New method.
	* eval.c (parse_and_eval_type): Use first_opcode.
	* dtrace-probe.c (dtrace_process_dof_probe): Use first_opcode.

1 files changed, 7 insertions, 0 deletions

diff --git a/gdb/expression.h b/gdb/expression.h
index 0c4dc7b..c07111c 100644
--- a/gdb/expression.h
+++ b/gdb/expression.h
@@ -91,6 +91,13 @@ struct expression
 
   void resize (size_t);
 
+  /* Return the opcode for the outermost sub-expression of this
+     expression.  */
+  enum exp_opcode first_opcode () const
+  {
+      return elts[0].opcode;
+  }
+
   /* Language it was entered in.  */
   const struct language_defn *language_defn;
   /* Architecture it was parsed in.  */