IrTypes: fix ir2cfg

(cherry picked from commit cf162c7)

compiler/ir/ir.ir2cfg/src/org/jetbrains/kotlin/ir2cfg/generators/FunctionGenerator.kt

@@ -1,28 +1,16 @@
 /*
- * Copyright 2010-2016 JetBrains s.r.o.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * Copyright 2010-2018 JetBrains s.r.o. 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.ir2cfg.generators
 
-import org.jetbrains.kotlin.builtins.KotlinBuiltIns
 import org.jetbrains.kotlin.ir.IrElement
 import org.jetbrains.kotlin.ir.IrStatement
 import org.jetbrains.kotlin.ir.declarations.IrFunction
 import org.jetbrains.kotlin.ir.declarations.IrVariable
 import org.jetbrains.kotlin.ir.expressions.*
-import org.jetbrains.kotlin.ir.types.impl.originalKotlinType
+import org.jetbrains.kotlin.ir.types.isNothing
 import org.jetbrains.kotlin.ir.util.dump
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import org.jetbrains.kotlin.ir2cfg.graph.ControlFlowGraph
@@ -67,8 +55,7 @@ class FunctionGenerator(val function: IrFunction) {
             return result
         }
 
-        private fun IrElement?.isNothing() =
-            this is IrExpression && KotlinBuiltIns.isNothing(type.originalKotlinType!!) // TODO
+        private fun IrElement?.isNothing() = this is IrExpression && type.isNothing()
 
         override fun visitBlockBody(body: IrBlockBody, data: Boolean): IrStatement? {
             return body.process()