Revert "Revert "Make clang the default compiler on host.""

This reverts commit d54f3a6219bca6ae018f4395fa0f1254bd4459be.

Change-Id: Id96bb52a0d599f8848010d1589bdf0f70fc7124b
diff --git a/build/Android.common.mk b/build/Android.common.mk
index f58aabc..07f5cd3 100644
--- a/build/Android.common.mk
+++ b/build/Android.common.mk
@@ -93,11 +93,7 @@
 
 # Clang build support.
 ART_TARGET_CLANG := false
-ifeq ($(HOST_OS),darwin)
-  ART_HOST_CLANG := true
-else
-  ART_HOST_CLANG := false
-endif
+ART_HOST_CLANG := true
 
 # directory used for dalvik-cache on device
 ART_DALVIK_CACHE_DIR := /data/dalvik-cache
diff --git a/compiler/dex/frontend.cc b/compiler/dex/frontend.cc
index 243395a..3bd71d1 100644
--- a/compiler/dex/frontend.cc
+++ b/compiler/dex/frontend.cc
@@ -144,6 +144,12 @@
     return NULL;
   }
 
+  const CompilerOptions& compiler_options = driver.GetCompilerOptions();
+  CompilerOptions::CompilerFilter compiler_filter = compiler_options.GetCompilerFilter();
+  if (compiler_filter == CompilerOptions::kInterpretOnly) {
+    return nullptr;
+  }
+
   ClassLinker* class_linker = Runtime::Current()->GetClassLinker();
   CompilationUnit cu(driver.GetArenaPool());
 
@@ -210,9 +216,6 @@
     cu.mir_graph->EnableOpcodeCounting();
   }
 
-  const CompilerOptions& compiler_options = cu.compiler_driver->GetCompilerOptions();
-  CompilerOptions::CompilerFilter compiler_filter = compiler_options.GetCompilerFilter();
-
   // Check early if we should skip this compilation if using the profiled filter.
   if (cu.compiler_driver->ProfilePresent()) {
     std::string methodname = PrettyMethod(method_idx, dex_file);
diff --git a/compiler/dex/verification_results.cc b/compiler/dex/verification_results.cc
index 6b0875c..a7f67e7 100644
--- a/compiler/dex/verification_results.cc
+++ b/compiler/dex/verification_results.cc
@@ -30,11 +30,11 @@
 namespace art {
 
 VerificationResults::VerificationResults(const CompilerOptions* compiler_options)
-    : compiler_options_(compiler_options),
-      verified_methods_lock_("compiler verified methods lock"),
+    : verified_methods_lock_("compiler verified methods lock"),
       verified_methods_(),
       rejected_classes_lock_("compiler rejected classes lock"),
       rejected_classes_() {
+  UNUSED(compiler_options);
 }
 
 VerificationResults::~VerificationResults() {
diff --git a/compiler/dex/verification_results.h b/compiler/dex/verification_results.h
index 278182f..7fdf767 100644
--- a/compiler/dex/verification_results.h
+++ b/compiler/dex/verification_results.h
@@ -56,8 +56,6 @@
                                    const uint32_t access_flags);
 
   private:
-    const CompilerOptions* compiler_options_;
-
     // Verified methods.
     typedef SafeMap<MethodReference, const VerifiedMethod*,
         MethodReferenceComparator> VerifiedMethodMap;
diff --git a/compiler/driver/compiler_driver.h b/compiler/driver/compiler_driver.h
index 12463a9..817da17 100644
--- a/compiler/driver/compiler_driver.h
+++ b/compiler/driver/compiler_driver.h
@@ -564,8 +564,11 @@
   class ProfileData {
    public:
     ProfileData() : count_(0), method_size_(0), percent_(0) {}
-    ProfileData(std::string method_name, uint32_t count, uint32_t method_size, double percent) :
+    ProfileData(const std::string& method_name, uint32_t count, uint32_t method_size, double percent) :
       method_name_(method_name), count_(count), method_size_(method_size), percent_(percent) {
+      // TODO: currently method_size_ and count_ are unused.
+      UNUSED(method_size_);
+      UNUSED(count_);
     }
 
     bool IsAbove(double v) const { return percent_ >= v; }
diff --git a/runtime/thread_list.h b/runtime/thread_list.h
index 58bd92a..a574340 100644
--- a/runtime/thread_list.h
+++ b/runtime/thread_list.h
@@ -90,9 +90,8 @@
       LOCKS_EXCLUDED(Locks::thread_list_lock_,
                      Locks::thread_suspend_count_lock_);
 
-  size_t RunCheckpointOnRunnableThreads(Closure* checkpoint_function);
-      LOCKS_EXCLUDED(Locks::thread_list_lock_,
-                 Locks::thread_suspend_count_lock_);
+  size_t RunCheckpointOnRunnableThreads(Closure* checkpoint_function)
+      LOCKS_EXCLUDED(Locks::thread_list_lock_, Locks::thread_suspend_count_lock_);
 
   // Suspends all threads
   void SuspendAllForDebugger()