Fix isa swizzling for Kotlin subclasses of Obj-C classes

Don't rely on indexed ivars of instance's isa since isa swizzling
replaces it. Use method instead, it works on the replacement too
(if it is a subclass of the original isa).

 #KT-42482 Fixed.

kotlin-native/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/llvm/KotlinObjCClassInfoGenerator.kt

@@ -5,9 +5,9 @@
 
 package org.jetbrains.kotlin.backend.konan.llvm
 
-import llvm.LLVMStoreSizeOfType
+import llvm.LLVMLinkage
+import llvm.LLVMSetLinkage
 import llvm.LLVMValueRef
-import org.jetbrains.kotlin.backend.common.atMostOne
 import org.jetbrains.kotlin.backend.konan.*
 import org.jetbrains.kotlin.backend.konan.descriptors.getAnnotationStringValue
 import org.jetbrains.kotlin.backend.konan.ir.*
@@ -65,7 +65,9 @@ internal class KotlinObjCClassInfoGenerator(override val context: Context) : Con
                 staticData.placeGlobal(
                         "kobjcclassptr:${irClass.fqNameForIrSerialization}#internal",
                         NullPointer(int8Type)
-                ).pointer
+                ).pointer,
+
+                generateClassDataImp(irClass)
         )
 
         objCLLvmDeclarations.classInfoGlobal.setInitializer(info)
@@ -131,6 +133,26 @@ internal class KotlinObjCClassInfoGenerator(override val context: Context) : Con
                 )
             }
 
+    private fun generateClassDataImp(irClass: IrClass): ConstPointer {
+        val classDataPointer = staticData.placeGlobal(
+                "kobjcclassdata:${irClass.fqNameForIrSerialization}#internal",
+                Zero(runtime.kotlinObjCClassData)
+        ).pointer
+
+        val functionType = functionType(classDataPointer.llvmType, false, int8TypePtr, int8TypePtr)
+        val functionName = "kobjcclassdataimp:${irClass.fqNameForIrSerialization}#internal"
+
+        val function = generateFunction(codegen, functionType, functionName) {
+            ret(classDataPointer.llvm)
+        }.also {
+            LLVMSetLinkage(it, LLVMLinkage.LLVMPrivateLinkage)
+        }
+
+        return constPointer(function)
+    }
+
+    private val codegen = CodeGenerator(context)
+
     companion object {
         const val createdClassFieldIndex = 11
     }

kotlin-native/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/llvm/Runtime.kt

@@ -44,6 +44,7 @@ class Runtime(bitcodeFile: String) {
 
     val targetData = LLVMCreateTargetData(dataLayout)!!
 
+    val kotlinObjCClassData by lazy { getStructType("KotlinObjCClassData") }
     val kotlinObjCClassInfo by lazy { getStructType("KotlinObjCClassInfo") }
     val objCMethodDescription by lazy { getStructType("ObjCMethodDescription") }
     val objCTypeAdapter by lazy { getStructType("ObjCTypeAdapter") }

kotlin-native/backend.native/tests/interop/objc/tests/kt42482.h

@@ -0,0 +1,10 @@
+#import <Foundation/NSObject.h>
+
+extern BOOL kt42482Deallocated;
+extern id kt42482Global;
+
+@interface KT42482 : NSObject
+-(int)fortyTwo;
+@end;
+
+void kt42482Swizzle(id obj);

kotlin-native/backend.native/tests/interop/objc/tests/kt42482.kt

@@ -0,0 +1,35 @@
+import kotlin.native.ref.WeakReference
+import kotlinx.cinterop.*
+import kotlin.test.*
+import objcTests.*
+
+@Test
+fun testKT42482() {
+    // Attempt to make the state predictable:
+    kotlin.native.internal.GC.collect()
+
+    kt42482Deallocated = false
+    assertFalse(kt42482Deallocated);
+
+    {
+        assertEquals(41, KT42482().fortyTwo())
+
+        val obj: KT42482 = KT42482Impl()
+        assertEquals(42, obj.fortyTwo())
+
+        kt42482Swizzle(obj)
+        assertEquals(43, obj.fortyTwo())
+
+        // Test retain and release on swizzled object:
+        kt42482Global = obj
+        kt42482Global = null
+    }()
+
+    kotlin.native.internal.GC.collect()
+
+    assertTrue(kt42482Deallocated)
+}
+
+class KT42482Impl : KT42482() {
+    override fun fortyTwo() = 42
+}

kotlin-native/backend.native/tests/interop/objc/tests/kt42482.m

@@ -0,0 +1,36 @@
+#import "kt42482.h"
+#import "assert.h"
+#import <objc/runtime.h>
+
+BOOL kt42482Deallocated = NO;
+id kt42482Global = nil;
+
+@implementation KT42482
+-(int)fortyTwo {
+    return 41;
+}
+
+-(void)dealloc {
+    kt42482Deallocated = YES;
+}
+@end;
+
+int fortyTwoSwizzledImp(id self, SEL _cmd) {
+    return 43;
+}
+
+void kt42482Swizzle(id obj) {
+    Class oldClass = object_getClass(obj);
+
+    SEL selector = @selector(fortyTwo);
+
+    Class newClass = objc_allocateClassPair(oldClass, "KT42482Swizzled", 0);
+    assert(newClass != nil);
+    objc_registerClassPair(newClass);
+
+    Method method = class_getInstanceMethod([KT42482 class], selector);
+    assert(method != nil);
+    class_addMethod(newClass, selector, (IMP)&fortyTwoSwizzledImp, method_getTypeEncoding(method));
+
+    object_setClass(obj, newClass);
+}