Add synthesize uses at back edge.

This reduces the cost of linearizing the graph (hence removing
the notion of back edge). Since linear scan allocates/spills registers
based on next use, adding a use at a back edge ensures we do count
for loop uses.

Change-Id: Idaa882cb120edbdd08ca6bff142d326a8245bd14

3 files changed, 133 insertions, 0 deletions

diff --git a/test/482-checker-loop-back-edge-use/expected.txt b/test/482-checker-loop-back-edge-use/expected.txt
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/test/482-checker-loop-back-edge-use/expected.txt
diff --git a/test/482-checker-loop-back-edge-use/info.txt b/test/482-checker-loop-back-edge-use/info.txt
new file mode 100644
index 0000000000..f7fdefff88
--- /dev/null
+++ b/test/482-checker-loop-back-edge-use/info.txt
@@ -0,0 +1,2 @@
+Tests the register allocator's optimization of adding synthesized uses
+at back edges.
diff --git a/test/482-checker-loop-back-edge-use/src/Main.java b/test/482-checker-loop-back-edge-use/src/Main.java
new file mode 100644
index 0000000000..74184e8252
--- /dev/null
+++ b/test/482-checker-loop-back-edge-use/src/Main.java
@@ -0,0 +1,131 @@
+/*
+* 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 {
+
+  // CHECK-START: void Main.loop1(boolean) liveness (after)
+  // CHECK:         ParameterValue (liveness: 2 ranges: { [2, 22) }, uses: { 17 22 }
+  // CHECK:         Goto (liveness: 20)
+  public static void loop1(boolean incoming) {
+    while (incoming) {}
+  }
+
+  // CHECK-START: void Main.loop2(boolean) liveness (after)
+  // CHECK:         ParameterValue (liveness: 2 ranges: { [2, 42) }, uses: { 33 38 42 }
+  // CHECK:         Goto (liveness: 36)
+  // CHECK:         Goto (liveness: 40)
+  public static void loop2(boolean incoming) {
+    while (true) {
+      System.out.println("foo");
+      while (incoming) {}
+    }
+  }
+
+  // CHECK-START: void Main.loop3(boolean) liveness (after)
+  // CHECK:         ParameterValue (liveness: 2 ranges: { [2, 60) }, uses: { 56 60 }
+  // CHECK:         Goto (liveness: 58)
+
+  // CHECK-START: void Main.loop3(boolean) liveness (after)
+  // CHECK-NOT:     Goto (liveness: 54)
+  public static void loop3(boolean incoming) {
+    // 'incoming' only needs a use at the outer loop's back edge.
+    while (System.currentTimeMillis() != 42) {
+      while (Runtime.getRuntime() != null) {}
+      System.out.println(incoming);
+    }
+  }
+
+  // CHECK-START: void Main.loop4(boolean) liveness (after)
+  // CHECK:         ParameterValue (liveness: 2 ranges: { [2, 22) }, uses: { 22 }
+
+  // CHECK-START: void Main.loop4(boolean) liveness (after)
+  // CHECK-NOT:     Goto (liveness: 20)
+  public static void loop4(boolean incoming) {
+    // 'incoming' has no loop use, so should not have back edge uses.
+    System.out.println(incoming);
+    while (System.currentTimeMillis() != 42) {
+      while (Runtime.getRuntime() != null) {}
+    }
+  }
+
+  // CHECK-START: void Main.loop5(boolean) liveness (after)
+  // CHECK:         ParameterValue (liveness: 2 ranges: { [2, 50) }, uses: { 33 42 46 50 }
+  // CHECK:         Goto (liveness: 44)
+  // CHECK:         Goto (liveness: 48)
+  public static void loop5(boolean incoming) {
+    // 'incoming' must have a use at both back edges.
+    while (Runtime.getRuntime() != null) {
+      while (incoming) {
+        System.out.println(incoming);
+      }
+    }
+  }
+
+  // CHECK-START: void Main.loop6(boolean) liveness (after)
+  // CHECK          ParameterValue (liveness: 2 ranges: { [2, 46) }, uses: { 24 46 }
+  // CHECK:         Goto (liveness: 44)
+
+  // CHECK-START: void Main.loop6(boolean) liveness (after)
+  // CHECK-NOT:     Goto (liveness: 22)
+  public static void loop6(boolean incoming) {
+    // 'incoming' must have a use only at the first loop's back edge.
+    while (true) {
+      System.out.println(incoming);
+      while (Runtime.getRuntime() != null) {}
+    }
+  }
+
+  // CHECK-START: void Main.loop7(boolean) liveness (after)
+  // CHECK:         ParameterValue (liveness: 2 ranges: { [2, 50) }, uses: { 32 41 46 50 }
+  // CHECK:         Goto (liveness: 44)
+  // CHECK:         Goto (liveness: 48)
+  public static void loop7(boolean incoming) {
+    // 'incoming' must have a use at both back edges.
+    while (Runtime.getRuntime() != null) {
+      System.out.println(incoming);
+      while (incoming) {}
+    }
+  }
+
+  // CHECK-START: void Main.loop8() liveness (after)
+  // CHECK:         StaticFieldGet (liveness: 12 ranges: { [12, 44) }, uses: { 35 40 44 }
+  // CHECK:         Goto (liveness: 38)
+  // CHECK:         Goto (liveness: 42)
+  public static void loop8() {
+    // 'incoming' must have a use at both back edges.
+    boolean incoming = field;
+    while (Runtime.getRuntime() != null) {
+      while (incoming) {}
+    }
+  }
+
+  // CHECK-START: void Main.loop9() liveness (after)
+  // CHECK:         StaticFieldGet (liveness: 22 ranges: { [22, 36) }, uses: { 31 36 }
+  // CHECK:         Goto (liveness: 38)
+  public static void loop9() {
+    while (Runtime.getRuntime() != null) {
+      // 'incoming' must only have a use in the inner loop.
+      boolean incoming = field;
+      while (incoming) {}
+    }
+  }
+
+  public static void main(String[] args) {
+  }
+
+  static boolean field;
+}