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, 2 deletions

diff --git a/runtime/proxy_test.cc b/runtime/proxy_test.cc
index 308142157c..5af26b08b4 100644
--- a/runtime/proxy_test.cc
+++ b/runtime/proxy_test.cc
@@ -139,8 +139,9 @@ TEST_F(ProxyTest, ProxyClassHelper) {
   EXPECT_EQ(2U, proxy_class->NumDirectInterfaces());  // Interfaces$I and Interfaces$J.
   EXPECT_EQ(I.Get(), mirror::Class::GetDirectInterface(soa.Self(), proxy_class, 0));
   EXPECT_EQ(J.Get(), mirror::Class::GetDirectInterface(soa.Self(), proxy_class, 1));
-  std::string proxy_class_descriptor(proxy_class->GetDescriptor());
-  EXPECT_STREQ("L$Proxy1234;", proxy_class_descriptor.c_str());
+  std::string temp;
+  const char* proxy_class_descriptor = proxy_class->GetDescriptor(&temp);
+  EXPECT_STREQ("L$Proxy1234;", proxy_class_descriptor);
   EXPECT_EQ(nullptr, proxy_class->GetSourceFile());
 }