capture.swift

import Foundation
class SomeCallable {
   var completion: () -> Void = { }
   func call(completion: @escaping () -> Void) {
      // Do something
      self.completion = completion
   }
}
class SomeClass {
   var value: Int = 1
}

class SomeVCMock {
   let callable = SomeCallable()

   func viewDidLoad() {
      let some = SomeClass()
      callable.call { [some] in
         some.value = 0
      }
   }
}

git diff capture.sil no-capture.sil

   %2 = metatype $@thick SomeClass.Type            // user: %4
   // function_ref SomeClass.__allocating_init()
   %3 = function_ref @$s12swiftCapture9SomeClassCACycfC : $@convention(method) (@thick SomeClass.Type) -> @owned SomeClass // user: %4
-  %4 = apply %3(%2) : $@convention(method) (@thick SomeClass.Type) -> @owned SomeClass // users: %17, %16, %12, %11, %9, %8, %5
+  %4 = apply %3(%2) : $@convention(method) (@thick SomeClass.Type) -> @owned SomeClass // users: %14, %10, %9, %5
   debug_value %4 : $SomeClass, let, name "some"   // id: %5
   %6 = ref_element_addr %0 : $SomeVCMock, #SomeVCMock.callable // user: %7
-  %7 = load %6 : $*SomeCallable                   // users: %13, %14
-  strong_retain %4 : $SomeClass                   // id: %8
-  debug_value %4 : $SomeClass, let, name "some"   // id: %9
+  %7 = load %6 : $*SomeCallable                   // users: %11, %12
   // function_ref closure #1 in SomeVCMock.viewDidLoad()
-  %10 = function_ref @$s12swiftCapture10SomeVCMockC11viewDidLoadyyFyycfU_ : $@convention(thin) (@guaranteed SomeClass) -> () // user: %12
-  strong_retain %4 : $SomeClass                   // id: %11
-  %12 = partial_apply [callee_guaranteed] %10(%4) : $@convention(thin) (@guaranteed SomeClass) -> () // users: %15, %14
-  %13 = class_method %7 : $SomeCallable, #SomeCallable.call!1 : (SomeCallable) -> (@escaping () -> ()) -> (), $@convention(method) (@guaranteed @callee_guaranteed () -> (), @guaranteed SomeCallable) -> () // user: %14
-  %14 = apply %13(%12, %7) : $@convention(method) (@guaranteed @callee_guaranteed () -> (), @guaranteed SomeCallable) -> ()
-  strong_release %12 : $@callee_guaranteed () -> () // id: %15
-  strong_release %4 : $SomeClass                  // id: %16
-  strong_release %4 : $SomeClass                  // id: %17
-  %18 = tuple ()                                  // user: %19
-  return %18 : $()                                // id: %19
+  %8 = function_ref @$s12swiftCapture10SomeVCMockC11viewDidLoadyyFyycfU_ : $@convention(thin) (@guaranteed SomeClass) -> () // user: %10
+  strong_retain %4 : $SomeClass                   // id: %9
+  %10 = partial_apply [callee_guaranteed] %8(%4) : $@convention(thin) (@guaranteed SomeClass) -> () // users: %13, %12
+  %11 = class_method %7 : $SomeCallable, #SomeCallable.call!1 : (SomeCallable) -> (@escaping () -> ()) -> (), $@convention(method) (@guaranteed @callee_guaranteed () -> (), @guaranteed SomeCallable) -> () // user: %12
+  %12 = apply %11(%10, %7) : $@convention(method) (@guaranteed @callee_guaranteed () -> (), @guaranteed SomeCallable) -> ()
+  strong_release %10 : $@callee_guaranteed () -> () // id: %13
+  strong_release %4 : $SomeClass                  // id: %14
+  %15 = tuple ()                                  // user: %16
+  return %15 : $()                                // id: %16
 } // end sil function '$s12swiftCapture10SomeVCMockC11viewDidLoadyyF'

no-capture.swift

import Foundation
class SomeCallable {
   var completion: () -> Void = { }
   func call(completion: @escaping () -> Void) {
      // Do something
      self.completion = completion
   }
}
class SomeClass {
   var value: Int = 1
}

class SomeVCMock {
   let callable = SomeCallable()

   func viewDidLoad() {
      let some = SomeClass()
      callable.call {
         some.value = 0
      }
   }
}