CastOptimizer: don't assume dynamic casts from ObjectiveC classes to unrelated classes will fail

In case of ObjectiveC classes, the runtime type can differ from its declared type.
Therefore a cast between (compile-time) unrelated classes may succeed at runtime.

rdar://149810124

Author: eeckstein

lib/SIL/Utils/DynamicCasts.cpp

@@ -741,7 +741,10 @@ swift::classifyDynamicCast(SILFunction *function,
           if (targetClass->isSuperclassOf(sourceClass))
             return DynamicCastFeasibility::WillSucceed;
 
-          return DynamicCastFeasibility::WillFail;
+          // In case of ObjectiveC classes, the runtime type can differ from its
+          // declared type. Therefore a cast between (compile-time) unrelated
+          // classes may succeed at runtime.
+          return DynamicCastFeasibility::MaySucceed;
         }
       }
 
@@ -750,6 +753,12 @@ swift::classifyDynamicCast(SILFunction *function,
       if (hierarchyResult != DynamicCastFeasibility::WillFail)
         return hierarchyResult;
 
+      // In case of ObjectiveC classes, the runtime type can differ from its
+      // declared type. Therefore a cast between (compile-time) unrelated
+      // classes may succeed at runtime.
+      if (sourceClass->hasClangNode())
+        return DynamicCastFeasibility::MaySucceed;
+
       // As a backup, consider whether either type is a CF class type
       // with an NS bridged equivalent.
       CanType bridgedSource = getNSBridgedClassOfCFClass(source);

test/Interpreter/bridged_casts_folding.swift

@@ -58,7 +58,7 @@ Tests.test("NSString => Array<Int>. Crashing test case") {
   // CHECK: [       OK ] BridgedCastFolding.NSString => Array<Int>. Crashing test case
 
   // CHECK-OPT-LABEL: [ RUN      ] BridgedCastFolding.NSString => Array<Int>. Crashing test case
-  // CHECK-OPT: stderr>>> OK: saw expected "crashed: sig{{ill|trap}}"
+  // CHECK-OPT: stderr>>> OK: saw expected "crashed: sigabrt"
   // CHECK-OPT: [       OK ] BridgedCastFolding.NSString => Array<Int>. Crashing test case
   expectCrashLater()
   do {
@@ -130,7 +130,7 @@ Tests.test("NSNumber (Int) -> String. Crashing test.") {
   // CHECK: [       OK ] BridgedCastFolding.NSNumber (Int) -> String. Crashing test.
 
   // CHECK-OPT-LABEL: [ RUN      ] BridgedCastFolding.NSNumber (Int) -> String. Crashing test.
-  // CHECK-OPT: stderr>>> OK: saw expected "crashed: sig{{ill|trap}}"
+  // CHECK-OPT: stderr>>> OK: saw expected "crashed: sigabrt"
   // CHECK-OPT: [       OK ] BridgedCastFolding.NSNumber (Int) -> String. Crashing test.
   expectCrashLater()
   do {
@@ -393,7 +393,7 @@ Tests.test("String -> NSNumber. Crashing Test Case") {
   // CHECK: [       OK ] BridgedCastFolding.String -> NSNumber. Crashing Test Case
 
   // CHECK-OPT-LABEL: [ RUN      ] BridgedCastFolding.String -> NSNumber. Crashing Test Case
-  // CHECK-OPT: stderr>>> OK: saw expected "crashed: sig{{ill|trap}}"
+  // CHECK-OPT: stderr>>> OK: saw expected "crashed: sigabrt"
   // CHECK-OPT: [       OK ] BridgedCastFolding.String -> NSNumber. Crashing Test Case
   expectCrashLater()
   do {

test/SILOptimizer/cast_folding_no_bridging.sil

@@ -64,10 +64,8 @@ bb3:
 sil @fail : $@convention(thin) () -> Never
 
 // CHECK-LABEL: sil {{.*}}@testCFToObjC
-// CHECK: bb0(
-// CHECK-NEXT: [[T0:%.*]] = load %1 : $*CFString
-// CHECK-NEXT: [[T1:%.*]] = unchecked_ref_cast [[T0]] : $CFString to $NSString
-// CHECK-NEXT: store [[T1]] to %0 : $*NSString
+// CHECK:         checked_cast_addr_br
+// CHECK:       } // end sil function 'testCFToObjC'
 sil @testCFToObjC : $@convention(thin) (@in CFString) -> @out NSString {
 bb0(%0 : $*NSString, %1 : $*CFString):
   checked_cast_addr_br take_always CFString in %1 : $*CFString to NSString in %0 : $*NSString, bb1, bb2
@@ -83,11 +81,8 @@ bb2:
 }
 
 // CHECK-LABEL: sil {{.*}}@testCFToSwift
-// CHECK: bb0(
-// CHECK-NEXT: [[T0:%.*]] = load %1 : $*CFString
-// CHECK-NEXT: [[T1:%.*]] = unchecked_ref_cast [[T0]] : $CFString to $NSString
-// CHECK:      [[FN:%.*]] = function_ref @$sSS10FoundationE34_conditionallyBridgeFromObjectiveC_6resultSbSo8NSStringC_SSSgztFZ : $@convention(method) (@guaranteed NSString, @inout Optional<String>, @thin String.Type) -> Bool
-// CHECK: apply [[FN]]([[T1]], {{.*}}, {{.*}})
+// CHECK:         checked_cast
+// CHECK:       } // end sil function 'testCFToSwift'
 sil @testCFToSwift : $@convention(thin) (@in CFString) -> @out String {
 bb0(%0 : $*String, %1 : $*CFString):
   checked_cast_addr_br take_always CFString in %1 : $*CFString to String in %0 : $*String, bb1, bb2

test/SILOptimizer/cast_folding_objc.swift

@@ -77,12 +77,9 @@ public func castObjCToSwift<T>(_ t: T) -> Int {
   return t as! Int
 }
 
-// Check that compiler understands that this cast always fails
 // CHECK-LABEL: sil [noinline] {{.*}}@$s17cast_folding_objc37testFailingBridgedCastFromObjCtoSwiftySiSo8NSStringCF
-// CHECK: [[ONE:%[0-9]+]] = integer_literal $Builtin.Int1, -1
-// CHECK: cond_fail [[ONE]] : $Builtin.Int1, "failed cast"
-// CHECK-NEXT: unreachable
-// CHECK-NEXT: }
+// CHECK:         unconditional_checked_cast %0 : $NSString to NSNumber
+// CHECK:       } // end sil function '$s17cast_folding_objc37testFailingBridgedCastFromObjCtoSwiftySiSo8NSStringCF'
 @inline(never)
 public func testFailingBridgedCastFromObjCtoSwift(_ ns: NSString) -> Int {
   return castObjCToSwift(ns)