[SR-1111] Non-optimized builds should avoid redundant thick_to_objc_metatype conversions

[belkadan]

Previous ID	SR-1111
Radar	None
Original Reporter	@belkadan
Type	Improvement

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Improvement, IRGen, NotOptimizedOnly, StarterBug
Assignee	None
Priority	Medium

md5: ee5fa37243b2596a51a6125675863696

Issue Description:

In this code:

import Foundation
func test() -> Bool {
  let a = RunLoop.current
  let b = RunLoop.main
  return a === b
}

We're smart enough to avoid emitting two references to the metadata for NSRunLoop, but not smart enough (in -Onone builds) to avoid emitting the conversion to an ObjC Class twice, which involves a branch. We should be able to reuse the value from the first thick_to_objc_metatype conversion.