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, 3 insertions, 5 deletions

diff --git a/compiler/driver/compiler_driver.h b/compiler/driver/compiler_driver.h
index 2a5cdb9..233c4f8 100644
--- a/compiler/driver/compiler_driver.h
+++ b/compiler/driver/compiler_driver.h
@@ -92,8 +92,6 @@ class CompilerTls {
 
 class CompilerDriver {
  public:
-  typedef std::set<std::string> DescriptorSet;
-
   // Create a compiler targeting the requested "instruction_set".
   // "image" should be true if image specific optimizations should be
   // enabled.  "image_classes" lets the compiler know what classes it
@@ -105,7 +103,7 @@ class CompilerDriver {
                           Compiler::Kind compiler_kind,
                           InstructionSet instruction_set,
                           InstructionSetFeatures instruction_set_features,
-                          bool image, DescriptorSet* image_classes,
+                          bool image, std::set<std::string>* image_classes,
                           size_t thread_count, bool dump_stats, bool dump_passes,
                           CumulativeLogger* timer, std::string profile_file = "");
 
@@ -152,7 +150,7 @@ class CompilerDriver {
     return image_;
   }
 
-  DescriptorSet* GetImageClasses() const {
+  const std::set<std::string>* GetImageClasses() const {
     return image_classes_.get();
   }
 
@@ -729,7 +727,7 @@ class CompilerDriver {
   // If image_ is true, specifies the classes that will be included in
   // the image. Note if image_classes_ is NULL, all classes are
   // included in the image.
-  std::unique_ptr<DescriptorSet> image_classes_;
+  std::unique_ptr<std::set<std::string>> image_classes_;
 
   size_t thread_count_;
   uint64_t start_ns_;