[cxx-interop] Use unowned return convention for ObjC methods returning foreign reference types (#75640)

This fixes a runtime crash that occurs when a pointer to a foreign
reference type is passed to objc_retainAutoreleasedReturnValue.

This reverts 335cec0.

rdar://117353222

Author: ahatanaka

lib/IRGen/GenCall.cpp

@@ -39,7 +39,6 @@
 #include <optional>
 
 #include "CallEmission.h"
-#include "ClassTypeInfo.h"
 #include "EntryPointArgumentEmission.h"
 #include "Explosion.h"
 #include "GenCall.h"
@@ -2838,19 +2837,9 @@ class SyncCallEmission final : public CallEmission {
     if (fnConv.getNumDirectSILResults() == 1
         && (fnConv.getDirectSILResults().begin()->getConvention()
             == ResultConvention::Autoreleased)) {
-      if (IGF.IGM.Context.LangOpts.EnableObjCInterop) {
-        auto ty = fnConv.getSILResultType(IGF.IGM.getMaximalTypeExpansionContext());
-        // NOTE: We cannot dyn_cast directly to ClassTypeInfo since it does not
-        // implement 'classof', so will succeed for any ReferenceTypeInfo.
-        auto *refTypeInfo = dyn_cast<ReferenceTypeInfo>(&IGF.IGM.getTypeInfo(ty));
-        if (refTypeInfo && 
-            refTypeInfo->getReferenceCountingType() == ReferenceCounting::Custom) {
-          Explosion e(result);
-          refTypeInfo->as<ClassTypeInfo>().strongCustomRetain(IGF, e, true);
-        } else {
-          result = emitObjCRetainAutoreleasedReturnValue(IGF, result);
-        }
-      } else
+      if (IGF.IGM.Context.LangOpts.EnableObjCInterop)
+        result = emitObjCRetainAutoreleasedReturnValue(IGF, result);
+      else
         IGF.emitNativeStrongRetain(result, IGF.getDefaultAtomicity());
     }
 

lib/SIL/IR/SILFunctionType.cpp

@@ -3381,6 +3381,10 @@ class ObjCMethodConventions : public Conventions {
     // Otherwise, infer based on the method family.
     if (isImplicitPlusOneCFResult())
       return ResultConvention::Owned;
+
+    if (tl.getLoweredType().isForeignReferenceType())
+      return ResultConvention::Unowned;
+
     return ResultConvention::Autoreleased;
   }
 

test/Interop/Cxx/foreign-reference/reference-counted-objc-property.swift

@@ -9,17 +9,10 @@ import ReferenceCountedObjCProperty
 // CHECK: %[[LC:.*]] = alloca ptr, align {{4|8}}
 // CHECK: %[[V4:.*]] = load ptr, ptr @"\01L_selector(lc)", align {{4|8}}
 // CHECK: %[[V5:.*]] = call ptr @objc_msgSend(ptr %{{.*}}, ptr %[[V4]])
-// CHECK: %[[V6:.*]] = icmp ne ptr %[[V5]], null
-// CHECK: br i1 %[[V6]], label %[[LIFETIME_NONNULL_VALUE:.*]], label %[[LIFETIME_CONT:.*]]
-
-// CHECK: [[LIFETIME_NONNULL_VALUE]]:
-// CHECK-NEXT: call void @_Z8LCRetainPN2NS10LocalCountE(ptr %[[V5]])
-// CHECK-NEXT: br label %[[LIFETIME_CONT]]
-
-// CHECK: [[LIFETIME_CONT]]:
-// CHECK: store ptr %[[V5]], ptr %[[LC]], align {{4|8}}
-// CHECK: %[[TODESTROY:.*]] = load ptr, ptr %[[LC]], align {{4|8}}
-// CHECK: call void @_Z9LCReleasePN2NS10LocalCountE(ptr %[[TODESTROY]])
+// CHECK: call void @_Z8LCRetainPN2NS10LocalCountE(ptr %[[V5]])
+// CHECK: store ptr %[[V5]], ptr %[[LC]], align 8
+// CHECK: %[[TODESTROY:.*]] = load ptr, ptr %[[LC]], align 8
+// CHECK: call void @_Z9LCReleasePN2NS10LocalCountE(ptr %[[TODESTROY]]
 
 public func testGetter() {
   var c0 = C0()