[PATCH] D29670: [DebugInfo] Emit address space with DW_AT_address_class attribute for pointer and reference types

[David Blaikie via llvm-commits]

On Thu, Feb 16, 2017 at 2:10 PM Adrian Prantl via Phabricator <
reviews at reviews.llvm.org> wrote:

> aprantl added inline comments.
>
>
> ================
> Comment at: lib/Bitcode/Reader/MetadataLoader.cpp:1117
> +    Optional<unsigned> AddressSpace = None;
> +    if (Record.size() > 12 && Record[12] != ~0U)
> +      AddressSpace = Record[12];
> ----------------
> kzhuravl wrote:
> > dblaikie wrote:
> > > What's the magical ~0U value about?
> > I used it as a sentinel value to represent "None" optional dwarf address
> space in the bitcode (we always generate and read address space record, if
> it is ~0U, then we pass None when creating DIDerivedType).
> >
> > Would it be better to not write address space record if it is None?
> >
> > We can also use UINT24_MAX + 1 (we would need to define UINT24_MAX). or
> ADDRESS_SPACE_MAX?
> I'm pretty sure we prefer bitcode records from the same LLVM revision to
> always have the same number of elements.
> Typically we use 0 as the default value and omit it in the textual IR.
> What would you think about encoding the address space as n+1, with 0 being
> the default=None value?
>

I was going to say that seems a bit ugly (compared to using max value as
the marker) - but then rememered the bitcode format uses variable length
encoding, so encoding the max value probably isn't as cheap as zero, I
guess?

- Dave


>
>
> https://reviews.llvm.org/D29670
>
>
>
>
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