swift234

SILBuilder: peephole 'metatype' instruction used only by a thick/ObjC conversion instruction.

The 'metatype' instruction can produce either a thick or Objective-C
metatype value for a class. Sometimes SILGen picks the "wrong" one,
and ends up converting the value directly, which is sub-optimal. Clean
this up in SILBuilder.

I didn't add a corresponding SILCombine optimization, nor did I add
this for class_metatype, because it seems unlikely that those will
occur in practice.


Swift SVN r14183