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
diff --git a/benchmark/stringbuilder-append/src/StringBuilderAppendBenchmark.java b/benchmark/stringbuilder-append/src/StringBuilderAppendBenchmark.java
new file mode 100644
index 0000000..1550e81
--- /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();
+ }
+ }
+}
