Avoid use of std::string where we have const char*.

Removing the ClassHelper caused std::string creation for all calls to
Class::GetDescriptor and a significant performance regression. Make the
std::string an out argument so the caller can maintain it and its life time
while allowing GetDescriptor to return the common const char* case.

Don't generate GC maps when compilation is disabled.

Remove other uses of std::string that are occuring on critical paths.
Use the cheaper SkipClass in CompileMethod in CompilerDriver.
Specialize the utf8 as utf16 comparison code for the common shorter byte
encoding.
Force a bit of inlining, remove some UNLIKELYs (they are prone to pessimizing
code), add some LIKELYs.

x86-64 host 1-thread interpret-only of 57 apks:
Before: 29.539s
After: 23.467s

Regular compile:
Before: 1m35.347s
After: 1m20.056s

Bug: 16853450
Change-Id: Ic705ea24784bee24ab80084d06174cbf87d557ad

1 files changed, 7 insertions, 4 deletions

diff --git a/compiler/image_writer.cc b/compiler/image_writer.cc
index d102bbc..ba7e13f 100644
--- a/compiler/image_writer.cc
+++ b/compiler/image_writer.cc
@@ -294,7 +294,8 @@ void ImageWriter::ComputeEagerResolvedStrings() SHARED_LOCKS_REQUIRED(Locks::mut
 }
 
 bool ImageWriter::IsImageClass(Class* klass) {
-  return compiler_driver_.IsImageClass(klass->GetDescriptor().c_str());
+  std::string temp;
+  return compiler_driver_.IsImageClass(klass->GetDescriptor(&temp));
 }
 
 struct NonImageClasses {
@@ -351,7 +352,8 @@ void ImageWriter::PruneNonImageClasses() {
 bool ImageWriter::NonImageClassesVisitor(Class* klass, void* arg) {
   NonImageClasses* context = reinterpret_cast<NonImageClasses*>(arg);
   if (!context->image_writer->IsImageClass(klass)) {
-    context->non_image_classes->insert(klass->GetDescriptor());
+    std::string temp;
+    context->non_image_classes->insert(klass->GetDescriptor(&temp));
   }
   return true;
 }
@@ -371,14 +373,15 @@ void ImageWriter::CheckNonImageClassesRemovedCallback(Object* obj, void* arg) {
     Class* klass = obj->AsClass();
     if (!image_writer->IsImageClass(klass)) {
       image_writer->DumpImageClasses();
-      CHECK(image_writer->IsImageClass(klass)) << klass->GetDescriptor()
+      std::string temp;
+      CHECK(image_writer->IsImageClass(klass)) << klass->GetDescriptor(&temp)
                                                << " " << PrettyDescriptor(klass);
     }
   }
 }
 
 void ImageWriter::DumpImageClasses() {
-  CompilerDriver::DescriptorSet* image_classes = compiler_driver_.GetImageClasses();
+  const std::set<std::string>* image_classes = compiler_driver_.GetImageClasses();
   CHECK(image_classes != NULL);
   for (const std::string& image_class : *image_classes) {
     LOG(INFO) << " " << image_class;