[PATCH] IR: Add specialized debug info metadata nodes

[Adrian Prantl]

> On Feb 4, 2015, at 3:53 PM, Frédéric Riss <friss at apple.com> wrote:
> 
> 
>> On Feb 4, 2015, at 3:46 PM, Duncan P. N. Exon Smith <dexonsmith at apple.com> wrote:
>> 
>> 
>>> On 2015-Feb-04, at 15:37, Frédéric Riss <friss at apple.com> wrote:
>>> 
>>>>> 
>>>>> - The word 'context' is overloaded: `MDNode::getContext()` already
>>>>> exists, and returns an `LLVMContext&`; `DIDescriptor` uses 'context'
>>>>> to mean "the node that this one is defined inside".  I chose the
>>>>> word 'parent' instead of 'context' here.  Is this word okay?  If
>>>>> not, what about 'scope'?  This will be reflected in the assembly
>>>>> changes to come (I'd like the C++ names to match the assembly names,
>>>>> although technically it's not necessary).
>>>>> 
>>>>> I'd /probably/ go with scope (we already have scope in the MDLocations, so that seems consistent), but fairly on-the-fence.
>>>>> 
>>>> 
>>>> Weirdly, I didn't even notice that :).  In that case I like 'scope'
>>>> better too.  I'll update to that before commit.
>>> 
>>> Seems most natural. Can the futur getScope() return something that doesn’t derive from MDScope?
>> 
>> I don't think so.
> 
> That was my impression also, and it makes it even more appropriate IMHO.
> 

Just a few general remarks to throw into the discussion:

- Would it make sense to use something like tablegen to generate the repetitive parts? I’m slightly worried about copy&paste bugs, moderately worried about refactoring it in the future.



As for scopes, there are several things that bug me about the current class hierarchy that we could fix now:
- DIFile should not be a scope (the concept of files is IMO orthogonal to scoping and there is always something more appropriate to put a node into: compile unit, module, namespace)
- DIBasicType should not be scope
- It’s questionable whether a DICompositetype should be a DIDerivedType
- A DISubroutineType should be neither a DIDerivedType nor DIScope
- Using DIDerivedTypes for CV qualifiers is a bit wasteful but it does map nicely to DWARF

otherwise, thanks for doing this!
-- adrian
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