A char array copy optimization (libcore).

- Based on measurements, copy char by char for arrays of length <= 64.
- With this change, the Ritz MemAllocBench got ~25% faster on Nexus 4
  and ~20% faster on host.
- This change only handles arraycopy calls in the core libraries and
  char arrays with the rest future work.

Bug: 7103825

(cherry picked from commit a3eb10feba1c3479ad99ef5c5323d011a5365f4b)

Change-Id: Ic002ced3bc2f2a682cd4b8cec07ede990edd7463

1 files changed, 40 insertions, 0 deletions

diff --git a/benchmarks/src/benchmarks/SystemArrayCopyBenchmark.java b/benchmarks/src/benchmarks/SystemArrayCopyBenchmark.java
new file mode 100644
index 0000000..c22e819
--- /dev/null
+++ b/benchmarks/src/benchmarks/SystemArrayCopyBenchmark.java
@@ -0,0 +1,40 @@
+/*
+ * Copyright (C) 2013 Google Inc.
+ *
+ * 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.
+ */
+
+package benchmarks;
+
+import com.google.caliper.Param;
+import com.google.caliper.SimpleBenchmark;
+
+public class SystemArrayCopyBenchmark extends SimpleBenchmark {
+  @Param({"2", "4", "8", "16", "32", "64", "128", "256", "512", "1024",
+          "2048", "4096", "8192", "16384", "32768", "65536", "131072", "262144"})
+  int arrayLength;
+
+  // This copies a char array indirectly via String.getChars() as the
+  // System.arraycopy() call site optimization currently works within
+  // the core libraries only. Add direct System.arraycopy() benchmarks
+  // (including ones for other primitive types) later once this
+  // limitation goes away.
+  public void timeStringCharArrayCopy(int reps) {
+    final int len = arrayLength;
+    char[] dst = new char[len];
+    String str = new String(new char[len]);
+    for (int rep = 0; rep < reps; ++rep) {
+      str.getChars(0, len, dst, 0);
+    }
+  }
+}