1 /* 2 * Copyright (C) 2015 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 public class Main { foo(Object o, int a)18 public static void foo(Object o, int a) { 19 Object result = null; 20 if (o instanceof Main) { 21 // The compiler optimizes the type of `o` by introducing 22 // a `HBoundType` in this block. 23 while (a != 3) { 24 if (a == 2) { 25 a++; 26 result = o; 27 continue; 28 } else if (willInline()) { 29 // This block will be detected as dead after inlining. 30 result = new Object(); 31 continue; 32 } 33 result = new Object(); 34 } 35 // The compiler produces a phi at the back edge for `result`. 36 // Before dead block elimination, the phi has three inputs: 37 // result = (new Object(), new Object(), HBoundType) 38 // 39 // After dead block elimination, the phi has now two inputs: 40 // result = (new Object(), HBoundType) 41 // 42 // Our internal data structure for linking users and inputs expect 43 // the input index stored in that data structure to be the index 44 // in the inputs array. So the index before dead block elimination 45 // of the `HBoundType` would be 2. Dead block elimination must update 46 // that index to be 1. 47 } 48 System.out.println(result.getClass()); 49 } 50 willInline()51 public static boolean willInline() { 52 return false; 53 } 54 main(String[] args)55 public static void main(String[] args) { 56 foo(new Main(), 2); 57 } 58 } 59