From 552a13415573da19eafa46e1ac00fb0eb68f2b23 Mon Sep 17 00:00:00 2001
From: Vladimir Marko <vmarko@google.com>
Date: Tue, 31 Oct 2017 10:56:47 +0000
Subject: ART: Optimize StringBuilder append pattern.

Recognize appending with StringBuilder and replace the
entire expression with a runtime call that perfoms the
append in a more efficient manner.

For now, require the entire pattern to be in a single block
and be very strict about the StringBuilder environment uses.
Also, do not accept StringBuilder/char[]/Object/float/double
arguments as they throw non-OOME exceptions and/or require a
call from the entrypoint back to a helper function in Java;
these shall be implemented later.

Boot image size for aosp_taimen-userdebug:
 - before:
   arm/boot*.oat: 19653872
   arm64/boot*.oat: 23292784
   oat/arm64/services.odex: 22408664
 - after:
   arm/boot*.oat: 19432184 (-216KiB)
   arm64/boot*.oat: 22992488 (-293KiB)
   oat/arm64/services.odex: 22376776 (-31KiB)
Note that const-string in compiled boot image methods cannot
throw, but for apps it can and therefore its environment can
prevent the optimization for apps. We could implement either
a simple carve-out for const-string or generic environment
pruning to allow this pattern to be applied more often.

Results for the new StringBuilderAppendBenchmark on taimen:
  timeAppendLongStrings: ~700ns -> ~200ns
  timeAppendStringAndInt: ~220ns -> ~140ns
  timeAppendStrings: ~200ns -> 130ns

Bug: 19575890
Test: 697-checker-string-append
Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Test: aosp_taimen-userdebug boots.
Test: run-gtests.sh
Test: testrunner.py --target --optimizing
Test: vogar --benchmark art/benchmark/stringbuilder-append/src/StringBuilderAppendBenchmark.java
Change-Id: I51789bf299f5219f68ada4c077b6a1d3fe083964
---
 .../src/StringBuilderAppendBenchmark.java          | 62 ++++++++++++++++++++++
 1 file changed, 62 insertions(+)
 create mode 100644 benchmark/stringbuilder-append/src/StringBuilderAppendBenchmark.java

(limited to 'benchmark/stringbuilder-append/src/StringBuilderAppendBenchmark.java')

diff --git a/benchmark/stringbuilder-append/src/StringBuilderAppendBenchmark.java b/benchmark/stringbuilder-append/src/StringBuilderAppendBenchmark.java
new file mode 100644
index 0000000000..1550e81bf7
--- /dev/null
+++ b/benchmark/stringbuilder-append/src/StringBuilderAppendBenchmark.java
@@ -0,0 +1,62 @@
+/*
+ * Copyright (C) 2019 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 StringBuilderAppendBenchmark {
+    public static String string1 = "s1";
+    public static String string2 = "s2";
+    public static String longString1 = "This is a long string 1";
+    public static String longString2 = "This is a long string 2";
+    public static int int1 = 42;
+
+    public void timeAppendStrings(int count) {
+        String s1 = string1;
+        String s2 = string2;
+        int sum = 0;
+        for (int i = 0; i < count; ++i) {
+            String result = s1 + s2;
+            sum += result.length();  // Make sure the append is not optimized away.
+        }
+        if (sum != count * (s1.length() + s2.length())) {
+            throw new AssertionError();
+        }
+    }
+
+    public void timeAppendLongStrings(int count) {
+        String s1 = longString1;
+        String s2 = longString2;
+        int sum = 0;
+        for (int i = 0; i < count; ++i) {
+            String result = s1 + s2;
+            sum += result.length();  // Make sure the append is not optimized away.
+        }
+        if (sum != count * (s1.length() + s2.length())) {
+            throw new AssertionError();
+        }
+    }
+
+    public void timeAppendStringAndInt(int count) {
+        String s1 = string1;
+        int i1 = int1;
+        int sum = 0;
+        for (int i = 0; i < count; ++i) {
+            String result = s1 + i1;
+            sum += result.length();  // Make sure the append is not optimized away.
+        }
+        if (sum != count * (s1.length() + Integer.toString(i1).length())) {
+            throw new AssertionError();
+        }
+    }
+}
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