[llvm] r203488 - For functions with ARM target specific calling convention, when simplify-libcall

[Tim Northover]

> Even more, the backend knows the default calling convention for a
> target.

Agreed, if every C function emitted by Clang gets a PCS specifier then
something is probably very wonky. It could be made to work and might
even be natural for odd targets, but it's suspicious.

> So, plain C CC should "just work" and transform to AAPCS or AAPCS-VFP when necessary.

You could imagine a situation where some platform started out aapcs
and had to maintain that for existing libcalls for ABI compatibility,
but moved to aapcs_vfp for new additions. I don't know of any current
example though.

That's my main reason for wanting TargetLowering to have a say.

Cheers.

Tim.