fix bug when devirtualizing a begin_apply during inlining

When devirtualizing a `begin_apply`, it was passing the token's
use list to the conversion function when trying to convert the
yielded result. It's suppose to be the yielded result's list.

This became apparent when it encountered an access of a
`@_borrowed` property and we hit an assertion about an empty
use-list of a guaranteed value, when it was in fact the wrong list!

Author: kavon

lib/SILOptimizer/Utils/Devirtualize.cpp

@@ -559,7 +559,7 @@ replaceBeginApplyInst(SILBuilder &builder, SILLocation loc,
     auto newYield = newYields[i];
     // Insert any end_borrow if the yielded value before the token's uses.
     SmallVector<SILInstruction *, 4> users(
-      makeUserIteratorRange(oldBAI->getTokenResult()->getUses()));
+      makeUserIteratorRange(oldYield->getUses()));
     auto yieldCastRes = castValueToABICompatibleType(
       &builder, loc, newYield, newYield->getType(), oldYield->getType(),
       users);

test/SILOptimizer/mandatory_inlining_devirt.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend -sil-verify-all %s -module-name test -emit-sil -o - -verify | %FileCheck %s
+// RUN: %target-swift-frontend -sil-verify-all %s -module-name test -emit-sil -o - -verify | %FileCheck %s --enable-var-scope
 
 
 // Constructor calls are dispatched dynamically for open classes, even if
@@ -49,3 +49,19 @@ public func caller(_ c: Concrete) throws {
   // CHECK: try_apply [[FN]]([[ARG]]) : $@convention(method) (Concrete) -> @error any Error
   try callee(c)
 }
+
+
+public struct File {
+  var alias: FileHandle = FileHandle()
+}
+
+public class FileHandle {
+  @_borrowed var file: File = File()
+}
+
+// CHECK-LABEL: sil @$s4test20access_borrowed_readyAA10FileHandleCADF : $@convention(thin) (@guaranteed FileHandle) -> @owned FileHandle {
+public func access_borrowed_read(_ l: FileHandle) -> FileHandle {
+  // CHECK-NOT: begin_apply
+  // CHECK:     return
+  return l.file.alias
+}