IR: make lazyVar synchronized

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/lazyUtil.kt

@@ -8,15 +8,22 @@ package org.jetbrains.kotlin.ir.declarations.lazy
 import kotlin.properties.ReadWriteProperty
 import kotlin.reflect.KProperty
 
-fun <T> lazyVar(initializer: () -> T): ReadWriteProperty<Any?, T> = UnsafeLazyVar(initializer)
+fun <T> lazyVar(initializer: () -> T): ReadWriteProperty<Any?, T> = SynchronizedLazyVar(initializer)
 
-private class UnsafeLazyVar<T>(initializer: () -> T) : ReadWriteProperty<Any?, T> {
+private class SynchronizedLazyVar<T>(initializer: () -> T) : ReadWriteProperty<Any?, T> {
+    @Volatile
     private var isInitialized = false
+
     private var initializer: (() -> T)? = initializer
+
+    @Volatile
     private var _value: Any? = null
 
     private val value: T
         get() {
+            @Suppress("UNCHECKED_CAST")
+            if (isInitialized) return _value as T
+            synchronized(this) {
                 if (!isInitialized) {
                     _value = initializer!!()
                     isInitialized = true
@@ -25,13 +32,16 @@ private class UnsafeLazyVar<T>(initializer: () -> T) : ReadWriteProperty<Any?, T
                 @Suppress("UNCHECKED_CAST")
                 return _value as T
             }
+        }
 
     override fun toString(): String = if (isInitialized) value.toString() else "Lazy value not initialized yet."
 
     override fun getValue(thisRef: Any?, property: KProperty<*>): T = value
 
     override fun setValue(thisRef: Any?, property: KProperty<*>, value: T) {
+        synchronized(this) {
             this._value = value
             isInitialized = true
         }
     }
+}