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, 6 insertions, 0 deletions

diff --git a/runtime/entrypoints/quick/quick_entrypoints.h b/runtime/entrypoints/quick/quick_entrypoints.h
index 243f7ec1e2..954450fe7a 100644
--- a/runtime/entrypoints/quick/quick_entrypoints.h
+++ b/runtime/entrypoints/quick/quick_entrypoints.h
@@ -34,6 +34,7 @@ class Array;
 class Class;
 template<class MirrorType> class CompressedReference;
 class Object;
+class String;
 }  // namespace mirror
 
 class ArtMethod;
@@ -78,6 +79,11 @@ extern mirror::Object* JniMethodEndWithReferenceSynchronized(jobject result,
                                                              jobject locked, Thread* self)
     NO_THREAD_SAFETY_ANALYSIS HOT_ATTR;
 
+extern "C" mirror::String* artStringBuilderAppend(uint32_t format,
+                                                  const uint32_t* args,
+                                                  Thread* self)
+    REQUIRES_SHARED(Locks::mutator_lock_) HOT_ATTR;
+
 extern void ReadBarrierJni(mirror::CompressedReference<mirror::Object>* handle_on_stack,
                            Thread* self)
     NO_THREAD_SAFETY_ANALYSIS HOT_ATTR;