[LLVMdev] DIFactory interface is going away

[Duncan Sands]

Hi Devang,

>> It does make me wonder how you are supposed to represent types which cannot
>> be properly represented by LLVM types, for example structs with fields at
>> variable offsets from the start and/or of variable size; or structs with
>> fields that may or may not be present depending on the value of other fields.
>> Such types occur in Ada for example.
>
> The metadata constructs used to encode debugging information do not use (or refer) LLVM types directly.  Here is the interface to emit debug info for a member.

thanks for the explanation.

>
>      /// createMemberType - Create debugging information entry for a member.
>      /// @param Name         Member name.
>      /// @param File         File where this member is defined.
>      /// @param LineNo       Line number.
>      /// @param SizeInBits   Member size.

For Ada this needs to be a Value* since it is dynamic.  But presumably this
interface is a direct mapping to the Dwarf specification, i.e. Dwarf itself
has no way of encoding a variable size here?

>      /// @param AlignInBits  Member alignment.
>      /// @param OffsetInBits Member offset.

This is likewise dynamic in general.

>      /// @param Flags        Flags to encode member attribute, e.g. private
>      /// @param Ty           Parent type.
>      DIType createMemberType(StringRef Name, DIFile File,
>                              unsigned LineNo, uint64_t SizeInBits,
>                              uint64_t AlignInBits, uint64_t OffsetInBits,
>                              unsigned Flags, DIType Ty);
>
>
> Of course,  the FE needs to know the offset, size, alignment etc... for each field as per source language. The Parent type here is also debug info entry for the enclosing structure/class. Regarding variable size fields, I am not sure how they are encoded in DWARF.

GCC outputs some language specific Dwarf tags for Ada, perhaps to handle these
kinds of mad types.

Ciao, Duncan.