A question about TYPE_ARG_TYPES

[Kazu Hirata]

Hi Ian,

>>I keep finding places in GCC sources that check whether a member of
>>TYPE_ARG_TYPES is 0.  For example,
>>
>>  for (link = TYPE_ARG_TYPES (function_or_method_type);
>>       link && TREE_VALUE (link);
>>       link = TREE_CHAIN (link))
>>    gen_type_die (TREE_VALUE (link), context_die);
>>
>>Notice that TREE_VALUE (link) is part of the loop condition.
>>
>>Now, do we ever allow a NULL in TYPE_ARG_TYPES?  If so, what does that
>>mean?  My guess is that soneone was trying to be cautious about
>>encountering a NULL in TYPE_ARG_TYPES.  (If that's the case, we should
>>be using gcc_assert instead.)
> 
> 
> Just guessing here, but what happens with an old-style function
> definition in C?
> 
> void f();

AFAIK, that gets TYPE_ARG_TYPES (...) == NULL, so we don't even get to evaluate 
TREE_VALUE (TYPE_ARG_TYPES (...)).

On IRC, Daniel Berlin claims that there are some weird cases where TREE_VALUE 
(TYPE_ARG_TYPES (...)) is NULL.  I'll keep putting gcc_assert to see what happens.

Kazu Hirata