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

[David Blaikie]

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.
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