[PATCH] D66352: Debug Info: Support for DW_AT_export_symbols for anonymous structs

[David Blaikie via Phabricator via llvm-commits]

dblaikie added a comment.

In D66352#1637678 <https://reviews.llvm.org/D66352#1637678>, @probinson wrote:

> Looking at the dwarfstd.org examples, without the flag (e.g., for DWARF v4) we should emit something like this:
>
>   <1> DW_TAG_struct_type
>           DW_AT_name "A"
>     <2> DW_TAG_struct_type
>             // no DW_AT_name
>         <3> DW_TAG_member
>               DW_AT_name "x"
>               DW_AT_type (int)
>     <4> DW_TAG_struct_type
>             // no DW_AT_name
>         <5> DW_TAG_member
>               DW_AT_name "y"
>               DW_AT_type (int)
>     <6> DW_TAG_member // this is A's member for the anonymous struct
>             // no DW_AT_name
>             DW_AT_type <2>
>     <7> DW_TAG_member // this is A's member for the unnamed struct
>             DW_AT_name "C"
>             DW_AT_type <4>
>
>
> which means the way the consumer knows to promote the members of `<2>` to the scope of `<1>` is that its only reference (from `<6>`) is via a member that is unnamed, and it knows NOT to promote the members of `<4>` because the reference to it is from a member that IS named.
>
> Seems cleaner to flag the struct in v5, especially as it has essentially zero size cost (DW_AT_export_names would use DW_FORM_flag_present).
>
> I'm aware that other languages can have different lookup rules, some of which really can't be expressed in DWARF and the consumer has to Just Know, if it's the kind of consumer that is expected to do name lookups.  And the consumer also has to be ready to do the more complicated thing for earlier DWARF versions that don't have the flag.  But if we have the flag, it seems like we ought to make use of it here.


Yeah, I can't argue much about not adding it here - given the low cost & extra expressivity.

But, yeah, if I were the one working on lldb, I'd be inclined to make this work correctly without/regardless of the flag (by looking at whether the unnamed struct was referenced from an unnamed member variable or not)


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