Switch to unrelated ObjHeader and ArrayHeader. (#160)

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

@@ -857,7 +857,7 @@ internal class CodeGeneratorVisitor(val context: Context) : IrElementVisitorVoid
             if (it is IrSpreadElement) {
                 val exp = evaluateExpression(it.expression)!!
                 val array = codegen.bitcast(codegen.kArrayHeaderPtr, exp)
-                val sizePtr = LLVMBuildStructGEP(codegen.builder, array, 1, "")
+                val sizePtr = LLVMBuildStructGEP(codegen.builder, array, 2, "")
                 return@map Element(exp, codegen.load(sizePtr!!), true)
             }
             val exp = evaluateExpression(it)!!

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

@@ -18,8 +18,7 @@ private fun StaticData.objHeader(containerOffsetNegative: Int, typeInfo: ConstPo
 
 private fun StaticData.arrayHeader(containerOffsetNegative: Int, typeInfo: ConstPointer, length: Int): Struct {
     assert (length >= 0)
-    val objHeader = objHeader(containerOffsetNegative, typeInfo)
-    return Struct(runtime.arrayHeaderType, objHeader, Int32(length))
+    return Struct(runtime.arrayHeaderType, typeInfo, Int32(containerOffsetNegative), Int32(length))
 }
 
 private fun requiredPadding(size: Int, align: Int): Int {

runtime/src/main/cpp/Arrays.cpp

@@ -13,7 +13,7 @@ extern "C" {
 
 // Array.kt
 KRef Kotlin_Array_get(KConstRef thiz, KInt index) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   if (static_cast<uint32_t>(index) >= array->count_) {
     ThrowArrayIndexOutOfBoundsException();
   }
@@ -21,7 +21,7 @@ KRef Kotlin_Array_get(KConstRef thiz, KInt index) {
 }
 
 void Kotlin_Array_set(KRef thiz, KInt index, KConstRef value) {
-  ArrayHeader* array = static_cast<ArrayHeader*>(thiz);
+  ArrayHeader* array = thiz->array();
   if (static_cast<uint32_t>(index) >= array->count_) {
     ThrowArrayIndexOutOfBoundsException();
   }
@@ -29,23 +29,23 @@ void Kotlin_Array_set(KRef thiz, KInt index, KConstRef value) {
 }
 
 KRef Kotlin_Array_clone(KConstRef thiz) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   ArrayHeader* result = ArrayContainer(
       array->type_info(), array->count_).GetPlace();
   memcpy(
       ArrayAddressOfElementAt(result, 0),
       ArrayAddressOfElementAt(array, 0),
       ArrayDataSizeBytes(array));
-  return result;
+  return result->obj();
 }
 
 KInt Kotlin_Array_getArrayLength(KConstRef thiz) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   return array->count_;
 }
 
 void Kotlin_Array_fillImpl(KRef thiz, KInt fromIndex, KInt toIndex, KRef value) {
-  ArrayHeader* array = static_cast<ArrayHeader*>(thiz);
+  ArrayHeader* array = thiz->array();
   if (fromIndex < 0 || toIndex < fromIndex || toIndex > array->count_) {
     ThrowArrayIndexOutOfBoundsException();
   }
@@ -57,8 +57,8 @@ void Kotlin_Array_fillImpl(KRef thiz, KInt fromIndex, KInt toIndex, KRef value)
 
 void Kotlin_Array_copyImpl(KConstRef thiz, KInt fromIndex,
                            KRef destination, KInt toIndex, KInt count) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
-  ArrayHeader* destinationArray = static_cast<ArrayHeader*>(destination);
+  const ArrayHeader* array = thiz->array();
+  ArrayHeader* destinationArray = destination->array();
    if (fromIndex < 0 || fromIndex + count > array->count_ ||
        toIndex < 0 || toIndex + count > destinationArray->count_) {
         ThrowArrayIndexOutOfBoundsException();
@@ -70,7 +70,7 @@ void Kotlin_Array_copyImpl(KConstRef thiz, KInt fromIndex,
 
 // Arrays.kt
 KByte Kotlin_ByteArray_get(KConstRef thiz, KInt index) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   if (static_cast<uint32_t>(index) >= array->count_) {
     ThrowArrayIndexOutOfBoundsException();
   }
@@ -78,7 +78,7 @@ KByte Kotlin_ByteArray_get(KConstRef thiz, KInt index) {
 }
 
 void Kotlin_ByteArray_set(KRef thiz, KInt index, KByte value) {
-  ArrayHeader* array = static_cast<ArrayHeader*>(thiz);
+  ArrayHeader* array = thiz->array();
   if (static_cast<uint32_t>(index) >= array->count_) {
     ThrowArrayIndexOutOfBoundsException();
   }
@@ -86,23 +86,23 @@ void Kotlin_ByteArray_set(KRef thiz, KInt index, KByte value) {
 }
 
 KRef Kotlin_ByteArray_clone(KConstRef thiz) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   ArrayHeader* result = ArrayContainer(
       theByteArrayTypeInfo, array->count_).GetPlace();
   memcpy(
       ByteArrayAddressOfElementAt(result, 0),
       ByteArrayAddressOfElementAt(array, 0),
       ArrayDataSizeBytes(array));
-  return result;
+  return result->obj();
 }
 
 KInt Kotlin_ByteArray_getArrayLength(KConstRef thiz) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   return array->count_;
 }
 
 KChar Kotlin_CharArray_get(KConstRef thiz, KInt index) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   if (static_cast<uint32_t>(index) >= array->count_) {
     ThrowArrayIndexOutOfBoundsException();
   }
@@ -110,7 +110,7 @@ KChar Kotlin_CharArray_get(KConstRef thiz, KInt index) {
 }
 
 void Kotlin_CharArray_set(KRef thiz, KInt index, KChar value) {
-  ArrayHeader* array = static_cast<ArrayHeader*>(thiz);
+  ArrayHeader* array = thiz->array();
   if (static_cast<uint32_t>(index) >= array->count_) {
     ThrowArrayIndexOutOfBoundsException();
   }
@@ -118,18 +118,18 @@ void Kotlin_CharArray_set(KRef thiz, KInt index, KChar value) {
 }
 
 KRef Kotlin_CharArray_clone(KConstRef thiz) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   ArrayHeader* result = ArrayContainer(
       theCharArrayTypeInfo, array->count_).GetPlace();
   memcpy(
       PrimitiveArrayAddressOfElementAt<KChar>(result, 0),
       PrimitiveArrayAddressOfElementAt<KChar>(array, 0),
       ArrayDataSizeBytes(array));
-  return result;
+  return result->obj();
 }
 
 KRef Kotlin_CharArray_copyOf(KConstRef thiz, KInt newSize) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   ArrayHeader* result = ArrayContainer(
       theCharArrayTypeInfo, newSize).GetPlace();
   KInt toCopy = array->count_ < newSize ?  array->count_ : newSize;
@@ -137,16 +137,16 @@ KRef Kotlin_CharArray_copyOf(KConstRef thiz, KInt newSize) {
       PrimitiveArrayAddressOfElementAt<KChar>(result, 0),
       PrimitiveArrayAddressOfElementAt<KChar>(array, 0),
       toCopy * sizeof(KChar));
-  return result;
+  return result->obj();
 }
 
 KInt Kotlin_CharArray_getArrayLength(KConstRef thiz) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   return array->count_;
 }
 
 KShort Kotlin_ShortArray_get(KConstRef thiz, KInt index) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   if (static_cast<uint32_t>(index) >= array->count_) {
     ThrowArrayIndexOutOfBoundsException();
   }
@@ -154,7 +154,7 @@ KShort Kotlin_ShortArray_get(KConstRef thiz, KInt index) {
 }
 
 void Kotlin_ShortArray_set(KRef thiz, KInt index, KShort value) {
-  ArrayHeader* array = static_cast<ArrayHeader*>(thiz);
+  ArrayHeader* array = thiz->array();
   if (static_cast<uint32_t>(index) >= array->count_) {
     ThrowArrayIndexOutOfBoundsException();
   }
@@ -162,23 +162,23 @@ void Kotlin_ShortArray_set(KRef thiz, KInt index, KShort value) {
 }
 
 KRef Kotlin_ShortArray_clone(KConstRef thiz) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   ArrayHeader* result = ArrayContainer(
       theShortArrayTypeInfo, array->count_).GetPlace();
   memcpy(
       PrimitiveArrayAddressOfElementAt<KShort>(result, 0),
       PrimitiveArrayAddressOfElementAt<KShort>(array, 0),
       ArrayDataSizeBytes(array));
-  return result;
+  return result->obj();
 }
 
 KInt Kotlin_ShortArray_getArrayLength(KConstRef thiz) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   return array->count_;
 }
 
 KInt Kotlin_IntArray_get(KConstRef thiz, KInt index) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   if (static_cast<uint32_t>(index) >= array->count_) {
     ThrowArrayIndexOutOfBoundsException();
   }
@@ -186,31 +186,31 @@ KInt Kotlin_IntArray_get(KConstRef thiz, KInt index) {
 }
 
 void Kotlin_IntArray_set(KRef thiz, KInt index, KInt value) {
-  ArrayHeader* array = static_cast<ArrayHeader*>(thiz);
+  ArrayHeader* array = thiz->array();
   if (static_cast<uint32_t>(index) >= array->count_) {
     ThrowArrayIndexOutOfBoundsException();
   }
   *PrimitiveArrayAddressOfElementAt<KInt>(array, index) = value;
 }
 
-ObjHeader* Kotlin_IntArray_clone(KConstRef thiz) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+KRef Kotlin_IntArray_clone(KConstRef thiz) {
+  const ArrayHeader* array = thiz->array();
   ArrayHeader* result = ArrayContainer(
       theIntArrayTypeInfo, array->count_).GetPlace();
   memcpy(
       PrimitiveArrayAddressOfElementAt<KInt>(result, 0),
       PrimitiveArrayAddressOfElementAt<KInt>(array, 0),
       ArrayDataSizeBytes(array));
-  return result;
+  return result->obj();
 }
 
 KInt Kotlin_IntArray_getArrayLength(KConstRef thiz) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   return array->count_;
 }
 
 void Kotlin_IntArray_fillImpl(KRef thiz, KInt fromIndex, KInt toIndex, KInt value) {
-  ArrayHeader* array = static_cast<ArrayHeader*>(thiz);
+  ArrayHeader* array = thiz->array();
   if (fromIndex < 0 || toIndex < fromIndex || toIndex >= array->count_) {
     ThrowArrayIndexOutOfBoundsException();
   }
@@ -221,8 +221,8 @@ void Kotlin_IntArray_fillImpl(KRef thiz, KInt fromIndex, KInt toIndex, KInt valu
 
 void Kotlin_IntArray_copyImpl(KConstRef thiz, KInt fromIndex,
                               KRef destination, KInt toIndex, KInt count) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
-  ArrayHeader* destinationArray = static_cast<ArrayHeader*>(destination);
+  const ArrayHeader* array = thiz->array();
+  ArrayHeader* destinationArray = destination->array();
   if (fromIndex < 0 || fromIndex + count > array->count_ ||
       toIndex < 0 || toIndex + count > destinationArray->count_) {
     ThrowArrayIndexOutOfBoundsException();
@@ -233,7 +233,7 @@ void Kotlin_IntArray_copyImpl(KConstRef thiz, KInt fromIndex,
 }
 
 KLong Kotlin_LongArray_get(KConstRef thiz, KInt index) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   if (static_cast<uint32_t>(index) >= array->count_) {
 
         ThrowArrayIndexOutOfBoundsException();
@@ -242,7 +242,7 @@ KLong Kotlin_LongArray_get(KConstRef thiz, KInt index) {
 }
 
 void Kotlin_LongArray_set(KRef thiz, KInt index, KLong value) {
-  ArrayHeader* array = static_cast<ArrayHeader*>(thiz);
+  ArrayHeader* array = thiz->array();
   if (static_cast<uint32_t>(index) >= array->count_) {
     ThrowArrayIndexOutOfBoundsException();
   }
@@ -250,23 +250,23 @@ void Kotlin_LongArray_set(KRef thiz, KInt index, KLong value) {
 }
 
 KRef Kotlin_LongArray_clone(KConstRef thiz) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   ArrayHeader* result = ArrayContainer(
       theLongArrayTypeInfo, array->count_).GetPlace();
   memcpy(
       PrimitiveArrayAddressOfElementAt<KLong>(result, 0),
       PrimitiveArrayAddressOfElementAt<KLong>(array, 0),
       ArrayDataSizeBytes(array));
-  return result;
+  return result->obj();
 }
 
 KInt Kotlin_LongArray_getArrayLength(KConstRef thiz) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   return array->count_;
 }
 
 KFloat Kotlin_FloatArray_get(KConstRef thiz, KInt index) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   if (static_cast<uint32_t>(index) >= array->count_) {
     ThrowArrayIndexOutOfBoundsException();
   }
@@ -274,31 +274,31 @@ KFloat Kotlin_FloatArray_get(KConstRef thiz, KInt index) {
 }
 
 void Kotlin_FloatArray_set(KRef thiz, KInt index, KFloat value) {
-  ArrayHeader* array = static_cast<ArrayHeader*>(thiz);
+  ArrayHeader* array = thiz->array();
   if (static_cast<uint32_t>(index) >= array->count_) {
     ThrowArrayIndexOutOfBoundsException();
   }
   *PrimitiveArrayAddressOfElementAt<KFloat>(array, index) = value;
 }
 
-ArrayHeader* Kotlin_FloatArray_clone(KConstRef thiz) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+KRef Kotlin_FloatArray_clone(KConstRef thiz) {
+  const ArrayHeader* array = thiz->array();
   ArrayHeader* result = ArrayContainer(
       theFloatArrayTypeInfo, array->count_).GetPlace();
   memcpy(
       PrimitiveArrayAddressOfElementAt<KFloat>(result, 0),
       PrimitiveArrayAddressOfElementAt<KFloat>(array, 0),
       ArrayDataSizeBytes(array));
-  return result;
+  return result->obj();
 }
 
 KInt Kotlin_FloatArray_getArrayLength(KConstRef thiz) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   return array->count_;
 }
 
 KDouble Kotlin_DoubleArray_get(KConstRef thiz, KInt index) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   if (static_cast<uint32_t>(index) >= array->count_) {
     ThrowArrayIndexOutOfBoundsException();
   }
@@ -306,7 +306,7 @@ KDouble Kotlin_DoubleArray_get(KConstRef thiz, KInt index) {
 }
 
 void Kotlin_DoubleArray_set(KRef thiz, KInt index, KDouble value) {
-  ArrayHeader* array = static_cast<ArrayHeader*>(thiz);
+  ArrayHeader* array = thiz->array();
   if (static_cast<uint32_t>(index) >= array->count_) {
     ThrowArrayIndexOutOfBoundsException();
   }
@@ -314,23 +314,23 @@ void Kotlin_DoubleArray_set(KRef thiz, KInt index, KDouble value) {
 }
 
 KRef Kotlin_DoubleArray_clone(KConstRef thiz) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   ArrayHeader* result = ArrayContainer(
       theDoubleArrayTypeInfo, array->count_).GetPlace();
   memcpy(
       PrimitiveArrayAddressOfElementAt<KDouble>(result, 0),
       PrimitiveArrayAddressOfElementAt<KDouble>(array, 0),
       ArrayDataSizeBytes(array));
-  return result;
+  return result->obj();
 }
 
 KInt Kotlin_DoubleArray_getArrayLength(KConstRef thiz) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   return array->count_;
 }
 
 KBoolean Kotlin_BooleanArray_get(KConstRef thiz, KInt index) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   if (static_cast<uint32_t>(index) >= array->count_) {
     ThrowArrayIndexOutOfBoundsException();
   }
@@ -338,7 +338,7 @@ KBoolean Kotlin_BooleanArray_get(KConstRef thiz, KInt index) {
 }
 
 void Kotlin_BooleanArray_set(KRef thiz, KInt index, KBoolean value) {
-  ArrayHeader* array = static_cast<ArrayHeader*>(thiz);
+  ArrayHeader* array = thiz->array();
   if (static_cast<uint32_t>(index) >= array->count_) {
     ThrowArrayIndexOutOfBoundsException();
   }
@@ -346,18 +346,18 @@ void Kotlin_BooleanArray_set(KRef thiz, KInt index, KBoolean value) {
 }
 
 KRef Kotlin_BooleanArray_clone(KConstRef thiz) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   ArrayHeader* result = ArrayContainer(
       theBooleanArrayTypeInfo, array->count_).GetPlace();
   memcpy(
       PrimitiveArrayAddressOfElementAt<KBoolean>(result, 0),
       PrimitiveArrayAddressOfElementAt<KBoolean>(array, 0),
       ArrayDataSizeBytes(array));
-  return result;
+  return result->obj();
 }
 
 KInt Kotlin_BooleanArray_getArrayLength(KConstRef thiz) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   return array->count_;
 }
 

runtime/src/main/cpp/Exceptions.cpp

@@ -36,8 +36,7 @@ class AutoFree {
 
 // TODO: this method ignores the encoding.
 KString CreateKotlinStringFromCString(const char* str) {
-  return static_cast<KString>(AllocStringInstance(
-      SCOPE_GLOBAL, str, strlen(str)));
+  return AllocStringInstance(SCOPE_GLOBAL, str, strlen(str))->array();
 }
 
 #ifdef __cplusplus
@@ -59,7 +58,7 @@ KRef GetCurrentStackTrace() {
 
   for (int i = 0; i < size; ++i) {
     KString symbol = CreateKotlinStringFromCString(symbols[i]);
-    Kotlin_Array_set(result, i, symbol);
+    Kotlin_Array_set(result, i, symbol->obj());
   }
 
   return result;

runtime/src/main/cpp/Memory.cpp

@@ -1,6 +1,8 @@
 #include <string.h>
 #include <stdlib.h>
 
+#include <cstddef> // for offsetof
+
 #include "Assert.h"
 #include "Exceptions.h"
 #include "Memory.h"
@@ -42,7 +44,7 @@ void ArrayContainer::Init(const TypeInfo* type_info, uint32_t elements) {
   if (header_) {
     header_->ref_count_ = CONTAINER_TAG_INCREMENT;
     GetPlace()->count_ = elements;
-    SetMeta(GetPlace(), type_info);
+    SetMeta(GetPlace()->obj(), type_info);
   }
 }
 
@@ -64,7 +66,7 @@ ArrayHeader* ArenaContainer::PlaceArray(const TypeInfo* type_info, int count) {
   if (!result) {
     return nullptr;
   }
-  SetMeta(result, type_info);
+  SetMeta(result->obj(), type_info);
   result->count_ = count;
   return result;
 }
@@ -74,6 +76,14 @@ extern "C" {
 #endif
 
 void InitMemory() {
+  RuntimeAssert(offsetof(ArrayHeader, type_info_)
+                ==
+                offsetof(ObjHeader,   type_info_),
+                "Layout mismatch");
+  RuntimeAssert(offsetof(ArrayHeader, container_offset_negative_)
+                ==
+                offsetof(ObjHeader  , container_offset_negative_),
+                "Layout mismatch");
   // TODO: initialize heap here.
 }
 
@@ -86,7 +96,7 @@ ObjHeader* AllocInstance(const TypeInfo* type_info, PlacementHint hint) {
 ObjHeader* AllocArrayInstance(
     const TypeInfo* type_info, PlacementHint hint, uint32_t elements) {
   RuntimeAssert(type_info->instanceSize_ < 0, "must be an array");
-  return ArrayContainer(type_info, elements).GetPlace();
+  return ArrayContainer(type_info, elements).GetPlace()->obj();
 }
 
 ObjHeader* AllocStringInstance(
@@ -96,7 +106,7 @@ ObjHeader* AllocStringInstance(
       ByteArrayAddressOfElementAt(result, 0),
       data,
       length);
-  return result;
+  return result->obj();
 }
 
 ObjHeader* InitInstance(

runtime/src/main/cpp/Memory.h

@@ -39,6 +39,8 @@ struct ContainerHeader {
   volatile uint32_t ref_count_;
 };
 
+struct ArrayHeader;
+
 // Header of every object.
 struct ObjHeader {
   const TypeInfo* type_info_;
@@ -63,10 +65,40 @@ struct ObjHeader {
     return reinterpret_cast<ContainerHeader*>(
         reinterpret_cast<uintptr_t>(this) - container_offset_negative_);
   }
+
+  // Unsafe cast to ArrayHeader. Use carefully!
+  ArrayHeader* array() { return reinterpret_cast<ArrayHeader*>(this); }
+  const ArrayHeader* array() const { return reinterpret_cast<const ArrayHeader*>(this); }
 };
 
-// Header of value type array objects.
-struct ArrayHeader : public ObjHeader {
+// Header of value type array objects. Keep layout in sync with that of object header.
+struct ArrayHeader {
+  const TypeInfo* type_info_;
+  container_offset_t container_offset_negative_;
+
+  const TypeInfo* type_info() const {
+    // TODO: for moving collectors use meta-objects approach:
+    //  - store tag in lower bit TypeInfo, which marks if meta-object is in place
+    //  - when reading type_info_ check if it is unaligned
+    //  - if it is, pointer points to the MetaObject
+    //  - otherwise this is direct pointer to TypeInfo
+    // Meta-object allows storing additional data associated with some objects,
+    // such as stable hash code.
+    return type_info_;
+  }
+
+  void set_type_info(const TypeInfo* type_info) {
+    type_info_ = type_info;
+  }
+
+  ContainerHeader* container() const {
+    return reinterpret_cast<ContainerHeader*>(
+        reinterpret_cast<uintptr_t>(this) - container_offset_negative_);
+  }
+
+  ObjHeader* obj() { return reinterpret_cast<ObjHeader*>(this); }
+  const ObjHeader* obj() const { return reinterpret_cast<const ObjHeader*>(this); }
+
   // Elements count. Element size is stored in instanceSize_ field of TypeInfo, negated.
   uint32_t count_;
 };

runtime/src/main/cpp/Natives.cpp

@@ -77,7 +77,7 @@ KInt Kotlin_String_getStringLength(KString thiz) {
 }
 
 KString Kotlin_String_fromUtf8Array(KConstRef thiz, KInt start, KInt size) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   RuntimeAssert(array->type_info() == theByteArrayTypeInfo, "Must use a byte array");
   if (start < 0 || size < 0 || start + size > array->count_) {
     ThrowArrayIndexOutOfBoundsException();
@@ -97,7 +97,7 @@ KString Kotlin_String_fromUtf8Array(KConstRef thiz, KInt start, KInt size) {
 }
 
 KString Kotlin_String_fromCharArray(KConstRef thiz, KInt start, KInt size) {
-  const ArrayHeader* array = static_cast<const ArrayHeader*>(thiz);
+  const ArrayHeader* array = thiz->array();
   RuntimeAssert(array->type_info() == theCharArrayTypeInfo, "Must use a byte array");
   if (start < 0 || size < 0 || start + size > array->count_) {
     ThrowArrayIndexOutOfBoundsException();
@@ -124,7 +124,7 @@ KRef Kotlin_String_toCharArray(KString string) {
     *PrimitiveArrayAddressOfElementAt<KChar>(result, index) =
         *ByteArrayAddressOfElementAt(string, index);
   }
-  return result;
+  return result->obj();
 }
 
 
@@ -151,8 +151,8 @@ KString Kotlin_String_plusImpl(KString thiz, KString other) {
 KBoolean Kotlin_String_equals(KString thiz, KConstRef other) {
   if (other == nullptr || other->type_info() != theStringTypeInfo) return false;
   // Important, due to literal internalization.
-  if (thiz == other) return true;
-  KString otherString = reinterpret_cast<KString>(other);
+  KString otherString = other->array();
+  if (thiz == otherString) return true;
   return thiz->count_ == otherString->count_ &&
       memcmp(ByteArrayAddressOfElementAt(thiz, 0),
              ByteArrayAddressOfElementAt(otherString, 0),