swift234

Add Builtin.unsafeGuaranteed and Builtin.unsafeGuaranteedEnd

These builtins can be used to denote a scope over which the parameter passed to
unsafeGuaranteed can be assume to be @guaranteed: That is there is another
reference that keeps the value alive.

  // Scope begin
  strong_retain %0 : $Foo
  %2 = builtin "unsafeGuaranteed"<Foo>(%0 : $Foo) : $(Foo, Builtin.Int8)
  %3 = tuple_extract %2 : $(Foo, Builtin.Int8), 0
  %4 = tuple_extract %2 : $(Foo, Builtin.Int8), 1
  %5 = class_method %3 : $Foo, #Foo.beep!1 : (Foo) -> () -> ()
  %6 = apply %5(%3) : $@convention(method) (@guaranteed Foo) -> ()
  strong_release %3 : $Foo
  %8 = builtin "unsafeGuaranteedEnd"(%4 : $Builtin.Int8) : $(
  // Scope end

is semantically equivalent to:

  sil @guaranteed_lifetime : $@convention(method) (@guaranteed Foo) -> () {
  bb(%3: $Foo):
    %5 = class_method %3 : $Foo, #Foo.beep!1 : (Foo) -> () -> ()
    %6 = apply %5(%3) : $@convention(method) (@guaranteed Foo) -> ()
  }

  ...

  // Scope begin
  apply @guaranteed_lifetime(%0)
  // Scope end