diff --git a/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/ir/IrUtils.kt b/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/ir/IrUtils.kt
index 3baabba0989..46645dc42dc 100644
--- a/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/ir/IrUtils.kt
+++ b/compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/ir/IrUtils.kt
@@ -661,6 +661,12 @@ fun IrExpression?.isPure(
                 if (valueDeclaration is IrVariable) !valueDeclaration.isVar
                 else true
             }
+            is IrTypeOperatorCall ->
+                (
+                        operator == IrTypeOperator.INSTANCEOF ||
+                                operator == IrTypeOperator.REINTERPRET_CAST ||
+                                operator == IrTypeOperator.NOT_INSTANCEOF
+                        ) && argument.isPure(anyVariable, checkFields, context)
             is IrCall -> if (context?.isSideEffectFree(this) == true) {
                 for (i in 0 until valueArgumentsCount) {
                     val valueArgument = getValueArgument(i)
diff --git a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsIrBackendContext.kt b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsIrBackendContext.kt
index e71a172659f..b27c605290b 100644
--- a/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsIrBackendContext.kt
+++ b/compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/JsIrBackendContext.kt
@@ -61,7 +61,8 @@ class JsIrBackendContext(
 
     override fun isSideEffectFree(call: IrCall): Boolean =
         call.symbol in intrinsics.primitiveToLiteralConstructor.values ||
-                call.symbol == intrinsics.arrayLiteral
+                call.symbol == intrinsics.arrayLiteral ||
+                call.symbol == intrinsics.arrayConcat
 
     val devMode = configuration[JSConfigurationKeys.DEVELOPER_MODE] ?: false
     val errorPolicy = configuration[JSConfigurationKeys.ERROR_TOLERANCE_POLICY] ?: ErrorTolerancePolicy.DEFAULT