[PATCH] AsmWriter/Bitcode: Support specialized debug nodes

[Duncan P. N. Exon Smith]

> On 2015-Feb-10, at 16:16, David Blaikie <dblaikie at gmail.com> wrote:
> 
> 
> 
> On Tue, Feb 10, 2015 at 4:05 PM, Adrian Prantl <aprantl at apple.com> wrote:
> A few nitpicky suggestions and questions:
> 
> - !MDSubrange(count: 30, lo: 2)
>   what about spelling out “low” and “high”?
> 
> +1

(Just saw this -- please see my reply to Adrian.)

> - do we still need the uniqueID on MDLexicalBlock? Could it be a distinct node instead?
> 
> We might need to go back & figure out what that uniqueID is for - the comments/code say something about templates, though I don't believe it (template instantiations would be distinct functions, so the lexical blocks would be distinct by virtue of referring to their distinct enclosing scopes)... 
>  

I imagine this is from macros:

    #define DO_SOMETHING(cond) \
      do {
        if (cond)
          foo();
        else
          bar();
      } while (false)

The `if` and `else` blocks are indistinguishable:

    scope: same parent scope, which includes `cond`
    file: instantiation file
    line: instantiation line
    column: instantiation column

So I think we do need *something* here.  I was planning to drop the
`unique_id` field and make these `distinct` instead when I moved these
into place.

Maybe I should do that first though?