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, 9 insertions, 0 deletions

diff --git a/compiler/optimizing/code_generator_mips.cc b/compiler/optimizing/code_generator_mips.cc
index 72334afa40..b3bce78940 100644
--- a/compiler/optimizing/code_generator_mips.cc
+++ b/compiler/optimizing/code_generator_mips.cc
@@ -9529,6 +9529,15 @@ void InstructionCodeGeneratorMIPS::VisitStaticFieldSet(HStaticFieldSet* instruct
                  instruction->GetValueCanBeNull());
 }
 
+void LocationsBuilderMIPS::VisitStringBuilderAppend(HStringBuilderAppend* instruction) {
+  codegen_->CreateStringBuilderAppendLocations(instruction, Location::RegisterLocation(V0));
+}
+
+void InstructionCodeGeneratorMIPS::VisitStringBuilderAppend(HStringBuilderAppend* instruction) {
+  __ LoadConst32(A0, instruction->GetFormat()->GetValue());
+  codegen_->InvokeRuntime(kQuickStringBuilderAppend, instruction, instruction->GetDexPc());
+}
+
 void LocationsBuilderMIPS::VisitUnresolvedInstanceFieldGet(
     HUnresolvedInstanceFieldGet* instruction) {
   FieldAccessCallingConventionMIPS calling_convention;