r246991 - When building the alloca for a local variable, set its name

[John McCall via cfe-commits]

> On Sep 8, 2015, at 10:52 AM, Chandler Carruth <chandlerc at gmail.com> wrote:
> None of my performance concerns were relevant to this change FWIW.
> 
> I think the reason that this got "fixed" was because people had a tendancy to *rely* on the name downstream when we made it always present. =/ Personally, I like having *no* names in a no-asserts build because it ensures that absolutely no one is relying on them -- we have debug information for that.
> 
> I wonder if the right way to help the debugging scenario (which is very real and painful) is to expose a flag for this, or to expose a way to take an IR file with debug info and synthesize nice names for as much as we can using the debug info?

It makes sense to me to have a codegen option to preserve some minimal set of descriptive names

John.