Remove many superfluous SmallString::str() calls.

Now that SmallString is a first-class citizen, most SmallString::str()
calls are not required. This patch removes a whole bunch of them, yet
there are lots more.

There are two use cases where str() is really needed:
1) To use one of StringRef member functions which is not available in
SmallString.
2) To convert to std::string, as StringRef implicitly converts while 
SmallString do not. We may wish to change this, but it may introduce
ambiguity.

llvm-svn: 232622

clang/lib/Tooling/JSONCompilationDatabase.cpp

@@ -176,7 +176,7 @@ JSONCompilationDatabase::getCompileCommands(StringRef FilePath) const {
 
   std::string Error;
   llvm::raw_string_ostream ES(Error);
-  StringRef Match = MatchTrie.findEquivalent(NativeFilePath.str(), ES);
+  StringRef Match = MatchTrie.findEquivalent(NativeFilePath, ES);
   if (Match.empty())
     return std::vector<CompileCommand>();
   llvm::StringMap< std::vector<CompileCommandRef> >::const_iterator
@@ -307,13 +307,13 @@ bool JSONCompilationDatabase::parse(std::string &ErrorMessage) {
       SmallString<128> AbsolutePath(
           Directory->getValue(DirectoryStorage));
       llvm::sys::path::append(AbsolutePath, FileName);
-      llvm::sys::path::native(AbsolutePath.str(), NativeFilePath);
+      llvm::sys::path::native(AbsolutePath, NativeFilePath);
     } else {
       llvm::sys::path::native(FileName, NativeFilePath);
     }
     IndexByFile[NativeFilePath].push_back(
         CompileCommandRef(Directory, Command));
-    MatchTrie.insert(NativeFilePath.str());
+    MatchTrie.insert(NativeFilePath);
   }
   return true;
 }