[PATCH] IR: Add specialized debug info metadata nodes

[Duncan P. N. Exon Smith]

> On 2015-Feb-04, at 16:44, Duncan P. N. Exon Smith <dexonsmith at apple.com> wrote:
> 
>> 
>> On 2015-Feb-04, at 16:17, Adrian Prantl <aprantl at apple.com> wrote:
>> 
>> 
>>> 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.
>> 
> 
> `tablegen` might make sense here, I'm not sure.  Frankly, I've never used
> it before, and it's not clear to me whether it would actually reduce the
> amount of code in this case vs. shifting it over to utils/tablegen (given
> the macro usage).
> 
> I think the way the APIs are written, the only real danger is a mismatch
> between `MDNodeKeyImpl<>` and the current fields in the class (I believe
> other mismatches would be caught by the compiler).  As long as the unit
> tests are updated along with any refactoring that happens I think the
> danger even there is fairly low.
> 
> I'm open to it if there's definite value, though.  Maybe as a follow-up?
> 
> @dblaikie: I've seen you poking around tablegen internals a fair bit; any
> thoughts on this one?
> 
>> <classllvm_1_1DIScope__inherit__graph.png>
>> 
>> 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
>> 
> 
> Definitely want to get to those :).  I think most of those are marked
> in the code as `TODO`s (except for the CV-qualifier comment).  But I'm
> planning to change the schema itself separately from the infrastructure
> for it to simplify the triage of any problems that come up (see comments
> in PR22264).
> 
>> otherwise, thanks for doing this!
>> -- adrian
> 

Here's an updated patch using "scope" instead of "parent" (and updated
to match r228242, from David's review of r228212).

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