[llvm] r221167 - IR: MDNode => Value: Instruction::getAllMetadataOtherThanDebugLoc()

[Duncan P. N. Exon Smith]

> On 2014-Nov-03, at 10:40, David Blaikie <dblaikie at gmail.com> wrote:
> 
> 
> 
> On Mon, Nov 3, 2014 at 10:13 AM, Duncan P. N. Exon Smith <dexonsmith at apple.com> wrote:
> Author: dexonsmith
> Date: Mon Nov  3 12:13:57 2014
> New Revision: 221167
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=221167&view=rev
> Log:
> IR: MDNode => Value: Instruction::getAllMetadataOtherThanDebugLoc()
> 
> Change `Instruction::getAllMetadataOtherThanDebugLoc()` from a vector of
> `MDNode` to one of `Value`.  Part of PR21433.
> 
> This does seem like a rather unfortunate loss in type safety - is there no common type here other than Value*? Should we introduce one.
> 
> (more broadly, I do wonder if there's some common API we could expose via MDNode so as not to end up with two kinds of metadata... but I've not really been able to wrap my head around this enough to have a well informed perspective)
>  

Because of the overlap in API between `User` and `MDNode` -- they both
have operands, but deal with them completely differently -- the only
sane common base class between `MDNode` and `MDUser`/`CustomMD` is
`Value`.  Otherwise, `MDNode` would have to inherit from `User`
somehow which is (IMO) significantly worse.

I threw some thoughts on a longer term fix into PR21438 [1] last week
though, since this is bothering me too.

[1]: http://llvm.org/bugs/show_bug.cgi?id=21438