[optimizing] Fix a bug in moving the null check to the user.

When taking the decision to move a null check to the user we did not
verify if the next instruction checks the same object.

Change-Id: I2f4533a4bb18aa4b0b6d5e419f37dcccd60354d2

3 files changed, 52 insertions, 0 deletions

diff --git a/test/479-regression-implicit-null-check/expected.txt b/test/479-regression-implicit-null-check/expected.txt
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/test/479-regression-implicit-null-check/expected.txt
diff --git a/test/479-regression-implicit-null-check/info.txt b/test/479-regression-implicit-null-check/info.txt
new file mode 100644
index 0000000..0bfca8c
--- /dev/null
+++ b/test/479-regression-implicit-null-check/info.txt
@@ -0,0 +1,2 @@
+Tests a regression in which we moved the null check to an instruction which
+checked a different object. This lead to valid null checks being elided.
diff --git a/test/479-regression-implicit-null-check/src/Main.java b/test/479-regression-implicit-null-check/src/Main.java
new file mode 100644
index 0000000..6b6f2e4
--- /dev/null
+++ b/test/479-regression-implicit-null-check/src/Main.java
@@ -0,0 +1,50 @@
+/*
+* Copyright (C) 2015 The Android Open Source Project
+*
+* 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.
+*/
+
+
+public class Main {
+  public int x = 0;
+
+  public Main(Main c) {
+    // After inlining the graph will look like:
+    //     NullCheck c
+    //     InstanceFieldGet c
+    //     InstanceFieldSet this 3
+    // The dead code will eliminate the InstanceFieldGet and we'll end up with:
+    //     NullCheck c
+    //     InstanceFieldSet this 3
+    // At codegen, when verifying if we can move the null check to the user,
+    // we should check that we actually have the same user (not only that the
+    // next instruction can do implicit null checks).
+    // In this case we should generate code for the NullCheck since the next
+    // instruction checks a different object.
+    c.willBeInlined();
+    x = 3;
+  }
+
+  private int willBeInlined() {
+    return x;
+  }
+
+  public static void main(String[] args) {
+    try {
+      new Main(null);
+      throw new RuntimeException("Failed to throw NullPointerException");
+    } catch (NullPointerException e) {
+      // expected
+    }
+  }
+}