[RFC] Fix for PR58201

[Jan Hubicka]

> Hi all, Jakub,
> 
> On 09/07/2013 01:16 PM, Jakub Jelinek wrote:
> >As I wrote in the PR, IMHO mangle_decl should
> >   location_t save_location = input_location;
> >   input_location = DECL_SOURCE_LOCATION (decl);
> >...
> >   input_location = save_location;
> >around the call,
> I had a look and I'm afraid this is already happening and isn't
> enough: in mangle_decl_string, the call of write_mangled_name is
> wrapped in exactly what you are suggesting. Or you mean something
> else?
> 
> Otherwise, I'm afraid we have to resort to what Jason too appears to
> find acceptable, thus what Honza proposed about UNKNOWN_LOCATION +
> the tweak to print_instantiation_partial_context_line (essentially
> just return immediately if loc == UNKNOWN_LOCATION, I think)

Yes, I think those two changes makes perfect case.  Middle end probably should
be more consistent about not setting input_locations beyhond of this point (it
does not really make much sense).  It is not how things works unforutnately -
RTL expansion still lives in statement at a time and uses input location to 
propagate things down and there are many other random setters of this variable.

I will try to audit things incrementally.  With the change to cgraphunit I made
this week all mangling ought to happen early (this is also not 100% true: in
some very special cases where we late access virtual tables through BINFOs, I
have independent fix for that).

Honza
> 
> Paolo.