Dynamic cast optimizer: Consider CF conversions via superclasses.

A conversion from, e.g., CFMutableDictionary to NSDictionary is still a CF bridging conversion,
even though it doesn't go directly through CFMutableDictionary's own bridged class type.
Fixes rdar://problem/51078136.

Author: jckarter

lib/SIL/DynamicCasts.cpp

@@ -292,10 +292,16 @@ CanType swift::getNSBridgedClassOfCFClass(ModuleDecl *M, CanType type) {
 
 static bool isCFBridgingConversion(ModuleDecl *M, SILType sourceType,
                                    SILType targetType) {
-  return (sourceType.getASTType() ==
-            getNSBridgedClassOfCFClass(M, targetType.getASTType()) ||
-          targetType.getASTType() ==
-            getNSBridgedClassOfCFClass(M, sourceType.getASTType()));
+  if (auto bridgedTarget =
+        getNSBridgedClassOfCFClass(M, targetType.getASTType())) {
+    return bridgedTarget->isExactSuperclassOf(sourceType.getASTType());
+  }
+  if (auto bridgedSource =
+        getNSBridgedClassOfCFClass(M, sourceType.getASTType())) {
+    return targetType.getASTType()->isExactSuperclassOf(bridgedSource);
+  }
+  
+  return false;
 }
 
 /// Try to classify the dynamic-cast relationship between two types.
@@ -868,7 +874,7 @@ namespace {
         value = getOwnedScalar(source, srcTL);
       }
       auto targetTy = target.LoweredType;
-      if (isCFBridgingConversion(SwiftModule, targetTy, value->getType())) {
+      if (isCFBridgingConversion(SwiftModule, value->getType(), targetTy)) {
         value = B.createUncheckedRefCast(Loc, value, targetTy.getObjectType());
       } else {
         value = B.createUpcast(Loc, value, targetTy.getObjectType());

test/SILOptimizer/cast_folding_objc.swift

@@ -354,3 +354,8 @@ public func testConditionalBridgedCastFromSwiftToNSObjectDerivedClass(_ s: Strin
 public func testForcedBridgedCastFromSwiftToNSObjectDerivedClass(_ s: String) -> MyString {
     return s as! MyString
 }
+
+// rdar://problem/51078136
+func foo(x: CFMutableDictionary) -> [AnyHashable:AnyObject]? {
+  return x as? [AnyHashable:AnyObject]
+}