r188739 - Revert "Revert "Revert "Revert "DebugInfo: Omit debug info for dynamic classes in TUs that do not have the vtable for that class""""

[Greg Clayton]

On Dec 18, 2013, at 11:34 AM, David Blaikie <dblaikie at gmail.com> wrote:

> 
> 
> 
> On Tue, Dec 17, 2013 at 6:04 PM, Greg Clayton <gclayton at apple.com> wrote:
> 
> On Dec 17, 2013, at 5:38 PM, David Blaikie <dblaikie at gmail.com> wrote:
> 
> >
> >
> >
> > On Tue, Dec 17, 2013 at 5:34 PM, Greg Clayton <gclayton at apple.com> wrote:
> > >
> > > >
> > > > b) -flimit-debug-info is worth, at a guess, somewhere between 1 and 5%. This vtable optimization is worth closer to 20%. That's /serious/ bloat to consider accepting.
> > >
> > > I don't consider bloat being something that helps us to completely define a type that is going to be use when debugging so we can show the entire type and its member variables to the user.
> > >
> > > How do you know which types are going to be needed by the user? What about types that are only declared but not defined in this translation unit? ("struct foo; foo *f;")
> >
> > I will say again what I have said before: if I need to re-create a type form DWARF, then I want all the information I need. In order to re-create an opaque "struct foo" for a pointer or reference, a declaration is fine. If I need to recreate a class, I want all of the base class info.
> >
> > And if someone dereferences that pointer in a debugger expression?
> 
> Then I have no problems because I was able to create a pointer type that clang can deal with. You won't see any data inside of it, but it is a legal AST type.
> 
> Sorry - no, I mean what happens when the user writes an expression in the debugger that dereferences that pointer and you need the definition of the type?
> 
> What I'm asking is something as simple as:
> 
> // client.cpp
> struct foo;
> void lib_call(foo *f);
> void client_code(foo *f) {
>   lib_call(f);
> }
> 
> // library.cpp
> struct foo {
>   int i;
> };
> void lib_call(foo *f) {
>   f->i = 3;
> }
> 
> Say - and the user is debugging the client, the DWARF compile_unit for client.cpp contains only a declaration of 'foo', and the user issues the debugger command "p f->i". What do you do? You have to go & find the definition in some other compile unit, possibly in another object file or even in another shared library, etc.

Yes we do have to go look for another type. But this doesn't cause us to have to find this type in order for the type to exist in the clang AST from which it comes. So yes, this is being dealt with by the debugger, but we still currently like to be able to correctly represent the types that are defined within an AST by having all of the information we need.