swift234

[Closure Specializer] check in a pass to specialize closure.

If we have function A calls function B with a closure C
func A {
  B(...) {
    // closure C
  }
}
and the inliner decides to not inline B into A, it may be beneficial to generate
a specialized version of B to have
func A {
  B_spec_with_C(..., arguments_to_closure_C)
}
 
SILCombine will optimize apply of partial_apply that are both in B_spec_with_C.
Then inliner can inline the closure to B_spec_with_C.

For profitability, we check the relative size of the callee B and the closure C.
We also check hotness of the callsite to B in A and callsites to the closure
inside B. For now, if closure is called inside a loop, we think it is
profitable.

I will add this to the pass manager in a follow-up patch.
rdar://16569736


Swift SVN r21216