Add hash map, reduce excessive hashing

Changed the class def index to use a HashMap instead of unordered_map
so that we can use FindWithHash to reduce how often we need to compute
hashes.

Fixed a bug in ClassLinker::UpdateClass where we didn't properly
handle classes with the same descriptor but different class loaders.
Introduced by previous CL.

Before (fb launch):
1.74% art::ComputeModifiedUtf8Hash(char const*)

After:
0.95% art::ComputeModifiedUtf8Hash(char const*)

Bug: 18054905
Bug: 16828525

Change-Id: Iba2ee37c9837289e0ea187800ba4af322225a994

(cherry picked from commit 564ff985184737977aa26c485d0c1a413e530705)

1 files changed, 4 insertions, 2 deletions

diff --git a/runtime/native/java_lang_VMClassLoader.cc b/runtime/native/java_lang_VMClassLoader.cc
index 45563d299c..35932e0b89 100644
--- a/runtime/native/java_lang_VMClassLoader.cc
+++ b/runtime/native/java_lang_VMClassLoader.cc
@@ -36,14 +36,16 @@ static jclass VMClassLoader_findLoadedClass(JNIEnv* env, jclass, jobject javaLoa
   }
   ClassLinker* cl = Runtime::Current()->GetClassLinker();
   std::string descriptor(DotToDescriptor(name.c_str()));
-  mirror::Class* c = cl->LookupClass(soa.Self(), descriptor.c_str(), loader);
+  const size_t descriptor_hash = ComputeModifiedUtf8Hash(descriptor.c_str());
+  mirror::Class* c = cl->LookupClass(soa.Self(), descriptor.c_str(), descriptor_hash, loader);
   if (c != nullptr && c->IsResolved()) {
     return soa.AddLocalReference<jclass>(c);
   }
   if (loader != nullptr) {
     // Try the common case.
     StackHandleScope<1> hs(soa.Self());
-    c = cl->FindClassInPathClassLoader(soa, soa.Self(), descriptor.c_str(), hs.NewHandle(loader));
+    c = cl->FindClassInPathClassLoader(soa, soa.Self(), descriptor.c_str(), descriptor_hash,
+                                       hs.NewHandle(loader));
     if (c != nullptr) {
       return soa.AddLocalReference<jclass>(c);
     }