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Re: [RFA] Add method overload resolution to expression parser

On 10/13/2009 02:24 PM, Tom Tromey wrote:
First, since this is an extension to C++, I wonder whether it will
introduce any parsing ambiguities once the parser is complete.  I
suspect not, but I thought you might have a better view.

If it does, I haven't found them yet. Unfortunately, for a vast majority of cases, I must largely rely on the test suite to highlight some errors. In this specific case, though, I don't believe the new rules are reachable except within a C++ context since they rely on OP_SCOPE. [If you try to use this with a C function, the code path is quite different. It cannot get to TYPE_INSTANCE.]

Keith> +exp : exp '(' nonempty_typelist ')' const_or_volatile

This is an interesting production.

Unfortunately, it is the only one that works. There are other rules that do a similar, sometimes non-sensical thing. The functional call rule is one example, e.g., "p (1+3)(5)" will attempt to call a function.

I would have expected it to explicitly look for maybe-qualified
identifiers -- not an arbitrary expression.  Does this let us do
something we could not otherwise do?  Or, what does this do:

print (return_a_function ()) (int)

This will not currently do anything -- the "(int)" part is ignored during evaluation. That's because all that the "(int)" part does is add TYPE_INSTANCE to the expression chain, which causes an expected type to be sent down to evaluate_subexp_standard. evaluate_subexp_standard largely ignores expect_type, so this acts as a nop.

Does it work to call an explicitly-specified overload?

print overloaded(int)(5)

(I assume from reading the patch that this works as expected.)

I never tried that, but it does work (for C++ methods -- again C functions do not work at all).

Keith>   func_mod:	'(' ')'
Keith>   			{ $$ = 0; }
Keith>   	|	'(' nonempty_typelist ')'
Keith>  -			{ free ($2); $$ = 0; }
Keith>  +			{ do_cleanups (typelist_cleanup); $$ = 0; }

I'm a bit surprised that the cleanup stuff works in the parser.

Daniel also mentions this in a later message. I'm not sure why I did it this way, but the code has changed (or it was a mistake) and it is certainly not needed. I've removed this and free the {re,m}alloc'd data in the TYPE_INSTANCE-generating rule.

Keith>  +static void
Keith>  +free_param_types (void *arg)

Needs a short intro comment.

This function has been removed.

Keith>  +static struct type *
Keith>  +make_params (int num_types, struct type **param_types)
Keith>  +  make_cleanup (free_param_types, type);

It is a little unusual to make a cleanup that isn't returned.  Is it
really safe in this case?  To know that, I think you'd have to examine
all callers of evaluate_subexp_standard.  It seems somewhat safer to do
explicit cleanups in the TYPE_INSTANCE case, what do you think?

This cleanup has also now been removed.

I've attached an updated patch which I think addresses most of the serious concerns.

From one of your follow-up messages, re: doing this in the parser:

The reason this is done during evaluation is because that is where the actual lookup of symbol is performed (unlike in C, where it is done in c_lex).


2009-11-09  Keith Seitz  <>

	* c-exp.y: Add new rule for resolving method overloads.
	* eval.c (make_params): New function.
	(evaluate_subexp_standard): Pass expect_type to value_aggregate_elt.
	Handle case TYPE_INSTANCE.
	(evaluate_subexp_for_address): Pass expect_type to value_aggregate_elt.
	* expression.h (enum exp_opcode): Add TYPE_INSTANCE.
	(compare_parameters): Add declaration.
	* parse.c (operator_length_standard): Add TYPE_INSTANCE.
	* valops.c (value_aggregate_elt): Add new expect_type parameter.
	Pass expect_type to value_struct_elt_for_reference.
	(value_struct_elt_for_reference): Add expect_type parameter and use
	Check for overload matches with and without artificial parameters.
	Skip artificial methods.
	(compare_parameters): New function.
	* value.h (value_aggregate_elt): Add new expect_type parameter.

2009-11-09  Keith Seitz  <>

	* gdb.cp/overload.exp: Add tests for resolving overloaded
	methods in expression parsing/evaluation.

Attachment: ovld-expr-2.patch
Description: Text document

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