Support casting of optional to optional for opaque values

Author: Joe Shajrawi

lib/SILGen/SILGenExpr.cpp

@@ -3334,8 +3334,9 @@ RValue RValueEmitter::visitOptionalEvaluationExpr(OptionalEvaluationExpr *E,
 
   // Form the optional using address operations if the type is address-only or
   // if we already have an address to use.
-  bool isByAddress = usingProvidedContext || optTL.isAddressOnly();
-  
+  bool isByAddress = ((usingProvidedContext || optTL.isAddressOnly()) &&
+                      SGF.silConv.useLoweredAddresses());
+
   std::unique_ptr<TemporaryInitialization> optTemp;
   if (!usingProvidedContext && isByAddress) {
     // Allocate the temporary for the Optional<T> if we didn't get one from the

test/SILGen/opaque_values_silgen.swift

@@ -710,6 +710,20 @@ func s360________guardEnum<T>(_ e: IndirectEnum<T>) {
   }
 }
 
+// Tests casting optional opaques to optional opaques
+// ---
+// CHECK-LABEL: sil hidden @_T020opaque_values_silgen21s370_____optToOptCastxSgSQyxGlF : $@convention(thin) <T> (@in Optional<T>) -> @out Optional<T> {
+// CHECK: bb0([[ARG:%.*]] : $Optional<T>):
+// CHECK:   [[BORROWED_ARG:%.*]] = begin_borrow [[ARG]]
+// CHECK:   [[COPY__ARG:%.*]] = copy_value [[BORROWED_ARG]]
+// CHECK:   end_borrow [[BORROWED_ARG]] from [[ARG]] : $Optional<T>, $Optional<T>
+// CHECK:   destroy_value [[ARG]]
+// CHECK:   return [[COPY__ARG]] : $Optional<T>
+// CHECK-LABEL: } // end sil function '_T020opaque_values_silgen21s370_____optToOptCastxSgSQyxGlF'
+func s370_____optToOptCast<T>(_ x : T!) -> T? {
+  return x
+}
+
 // Tests conditional value casts and correspondingly generated reabstraction thunk, with <T> types
 // ---
 // CHECK-LABEL: sil hidden @_T020opaque_values_silgen21s999_____condTFromAnyyyp_xtlF : $@convention(thin) <T> (@in Any, @in T) -> () {