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

1 files changed, 67 insertions, 0 deletions

diff --git a/runtime/string_builder_append.h b/runtime/string_builder_append.h
new file mode 100644
index 0000000000..fee64198f9
--- /dev/null
+++ b/runtime/string_builder_append.h
@@ -0,0 +1,67 @@
+/*
+ * 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.
+ */
+
+#ifndef ART_RUNTIME_STRING_BUILDER_APPEND_H_
+#define ART_RUNTIME_STRING_BUILDER_APPEND_H_
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include "base/bit_utils.h"
+#include "base/locks.h"
+#include "obj_ptr.h"
+
+namespace art {
+
+class Thread;
+
+namespace mirror {
+class String;
+}  // namespace mirror
+
+class StringBuilderAppend {
+ public:
+  enum class Argument : uint8_t {
+    kEnd = 0u,
+    kObject,
+    kStringBuilder,
+    kString,
+    kCharArray,
+    kBoolean,
+    kChar,
+    kInt,
+    kLong,
+    kFloat,
+    kDouble,
+    kLast = kDouble
+  };
+
+  static constexpr size_t kBitsPerArg =
+      MinimumBitsToStore(static_cast<size_t>(Argument::kLast));
+  static constexpr size_t kMaxArgs = BitSizeOf<uint32_t>() / kBitsPerArg;
+  static_assert(kMaxArgs * kBitsPerArg == BitSizeOf<uint32_t>(), "Expecting no extra bits.");
+  static constexpr uint32_t kArgMask = MaxInt<uint32_t>(kBitsPerArg);
+
+  static ObjPtr<mirror::String> AppendF(uint32_t format, const uint32_t* args, Thread* self)
+      REQUIRES_SHARED(Locks::mutator_lock_);
+
+ private:
+  class Builder;
+};
+
+}  // namespace art
+
+#endif  // ART_RUNTIME_STRING_BUILDER_APPEND_H_