[K/N] Make atomic ordering weaker for less performance harm

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

@@ -1,6 +1,6 @@
 /*
- * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * Copyright 2010-2022 JetBrains s.r.o. and Kotlin Programming Language contributors.
- * that can be found in the LICENSE file.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
 package org.jetbrains.kotlin.backend.konan
@@ -52,6 +52,7 @@ class KonanConfig(val project: Project, val configuration: CompilerConfiguration
     private val platformManager = PlatformManager(distribution)
     internal val targetManager = platformManager.targetManager(configuration.get(KonanConfigKeys.TARGET))
     internal val target = targetManager.target
+    val targetHasAddressDependency get() = target.hasAddressDependencyInMemoryModel()
     internal val phaseConfig = configuration.get(CLIConfigurationKeys.PHASE_CONFIG)!!
 
     // TODO: debug info generation mode and debug/release variant selection probably requires some refactoring.

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

@@ -1,6 +1,6 @@
 /*
- * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * Copyright 2010-2022 JetBrains s.r.o. and Kotlin Programming Language contributors.
- * that can be found in the LICENSE file.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
 package org.jetbrains.kotlin.backend.konan.llvm
@@ -1144,13 +1144,24 @@ internal abstract class FunctionGenerationContext(
 
     fun loadTypeInfo(objPtr: LLVMValueRef): LLVMValueRef {
         val typeInfoOrMetaPtr = structGep(objPtr, 0  /* typeInfoOrMeta_ */)
-        val typeInfoOrMetaWithFlags = load(typeInfoOrMetaPtr, memoryOrder = LLVMAtomicOrdering.LLVMAtomicOrderingAcquire)
+
+        val memoryOrder = if (context.config.targetHasAddressDependency) {
+            /**
+             * Formally, this ordering is too weak, and doesn't prevent data race with installing extra object.
+             * Check comment in ObjHeader::type_info for details.
+             */
+            LLVMAtomicOrdering.LLVMAtomicOrderingMonotonic
+        } else {
+            LLVMAtomicOrdering.LLVMAtomicOrderingAcquire
+        }
+
+        val typeInfoOrMetaWithFlags = load(typeInfoOrMetaPtr, memoryOrder = memoryOrder)
         // Clear two lower bits.
         val typeInfoOrMetaWithFlagsRaw = ptrToInt(typeInfoOrMetaWithFlags, codegen.intPtrType)
         val typeInfoOrMetaRaw = and(typeInfoOrMetaWithFlagsRaw, codegen.immTypeInfoMask)
         val typeInfoOrMeta = intToPtr(typeInfoOrMetaRaw, kTypeInfoPtr)
         val typeInfoPtrPtr = structGep(typeInfoOrMeta, 0 /* typeInfo */)
-        return load(typeInfoPtrPtr)
+        return load(typeInfoPtrPtr, memoryOrder = LLVMAtomicOrdering.LLVMAtomicOrderingMonotonic)
     }
 
     fun lookupInterfaceTableRecord(typeInfo: LLVMValueRef, interfaceId: Int): LLVMValueRef {

kotlin-native/runtime/src/main/cpp/Common.h

@@ -52,4 +52,9 @@
 #define KONAN_TYPE_INFO_HAS_WRITABLE_PART 1
 #endif
 
+// should be consistent with hasAddressDependencyInMemoryModel function
+#if defined(KONAN_X64) || defined(KONAN_X86) || defined(KONAN_ARM32) || defined(KONAN_ARM64)
+#define KONAN_TARGET_HAS_ADDRESS_DEPENDENCY 1
+#endif
+
 #endif // RUNTIME_COMMON_H

kotlin-native/runtime/src/main/cpp/Memory.h

@@ -62,8 +62,24 @@ struct ObjHeader {
   TypeInfo* typeInfoOrMetaRelaxed() const { return atomicGetRelaxed(&typeInfoOrMeta_);}
   TypeInfo* typeInfoOrMetaAcquire() const { return atomicGetAcquire(&typeInfoOrMeta_);}
 
+  /**
+   * Formally, this code data races with installing ExtraObject. Even though, we are okey, with reading
+   * both typeInfo and meta-object pointer, llvm memory model doesn't guarantee, that if we are able to
+   * see metaObject, written by other thread, we would be able to see metaObject->typeInfo.
+   *
+   * To make this correct with llvm memory model we need to use [LLVMAtomicOrdering.LLVMAtomicOrderingAcquire] here.
+   * Unfortunately, this is dramatically harmful for performance on arm architecture. So, we are using
+   * [LLVMAtomicOrdering.LLVMAtomicOrderingMonotonic] for both this read and following load of metaObject->typeInfo.
+   * At this point, we have no data race, but llvm memory model allows uninitialized value to be read from metaObject->typeInfo.
+   *
+   * Hardware guaranties on many supported platforms doesn't allow this to happen.
+   */
   const TypeInfo* type_info() const {
-    return clearPointerBits(typeInfoOrMetaAcquire(), OBJECT_TAG_MASK)->typeInfo_;
+#ifdef KONAN_TARGET_HAS_ADDRESS_DEPENDENCY
+      return atomicGetRelaxed(&clearPointerBits(typeInfoOrMetaRelaxed(), OBJECT_TAG_MASK)->typeInfo_);
+#else
+      return atomicGetRelaxed(&clearPointerBits(typeInfoOrMetaAcquire(), OBJECT_TAG_MASK)->typeInfo_);
+#endif
   }
 
   bool has_meta_object() const {

kotlin-native/runtime/src/mm/cpp/ExtraObjectData.hpp

@@ -78,7 +78,8 @@ public:
 
     // info must be equal to objHeader->type_info(), but it needs to be loaded in advance to avoid data races
     explicit ExtraObjectData(ObjHeader* objHeader, const TypeInfo *info) noexcept :
-        typeInfo_(info), weakReferenceCounterOrBaseObject_(objHeader) {
+        typeInfo_(nullptr), weakReferenceCounterOrBaseObject_(objHeader) {
+        atomicSetRelease(&typeInfo_, info);
     }
     ~ExtraObjectData();
 private:

kotlin-native/shared/src/main/kotlin/org/jetbrains/kotlin/konan/target/KonanTargetExtenstions.kt

@@ -1,3 +1,8 @@
+/*
+ * Copyright 2010-2022 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
 package org.jetbrains.kotlin.konan.target
 
 // TODO: This all needs to go to konan.properties
@@ -17,7 +22,7 @@ fun KonanTarget.supportsMimallocAllocator(): Boolean =
         is KonanTarget.MINGW_X86 -> true
         is KonanTarget.MINGW_X64 -> true
         is KonanTarget.MACOS_X64 -> true
-         is KonanTarget.MACOS_ARM64 -> true
+        is KonanTarget.MACOS_ARM64 -> true
         is KonanTarget.LINUX_ARM64 -> true
         is KonanTarget.LINUX_ARM32_HFP -> true
         is KonanTarget.ANDROID_X64 -> true
@@ -59,3 +64,10 @@ fun KonanTarget.supportedSanitizers(): List<SanitizerKind> =
         // TODO: Support macOS arm64
         else -> listOf()
     }
+
+// should be consistent with KONAN_TARGET_HAS_ADDRESS_DEPENDENCY macro
+fun KonanTarget.hasAddressDependencyInMemoryModel(): Boolean =
+     when (this.architecture) {
+         Architecture.X86, Architecture.X64, Architecture.ARM32, Architecture.ARM64 -> true
+         Architecture.MIPS32, Architecture.MIPSEL32, Architecture.WASM32 -> false
+     }