[PATCH] Wire up external debug type references in LLVM

[David Blaikie]

On Tue, Jul 14, 2015 at 12:13 PM, Adrian Prantl <aprantl at apple.com> wrote:

> Hi Eric & David,
>
> this patch implements bare-bones LVM support for external type references
> as previously discussed in http://reviews.llvm.org/D9612.
> This is a necessary prerequisite for bootstrapping the emission of debug
> info inside modules.
>
> - Add a FlagExternalTypeRef to DICompositeType. External types must have a
> unique identifier.
> - External type references are emitted in the short form
> DW_AT_type([DW_FORM_ref_sig8]) but the long form with an indirect reference
> is also supported (see test case for examples).
>

Knee-jerk reaction (haven't looked at the patch yet): Long form will be
necessary for all the implicit things (you won't know which implicit things
go in the module debug info, because you can't instantiate them ahead of
time - well, maybe you can in a SFINAE trap... - but then there's still
member function template implicit specializations and nested classes). It
might be best to implement the general form first, then look at an
optimization for the "has no children" case separately (& in a way that
applies to normal type unit references too)

What happens for that today? (I see you have a nested imported declaration
that's forcing the emission of the type declaration, I take it? What
happens if the type is also referenced separately - does it get a sig8
there too, or does it use the 4 byte section offset to refer to the type
declaration which has the sole sig8?)


>
> thanks,
> -- adrian
>
>
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