Avoid dubious IdentifierInfo::getNameStart() uses

These cases in particular were incurring an extra strlen() when we already knew
the length. They appear to be leftovers from when the interfaces worked with C
strings that have continued to compile due to the implicit StringRef ctor.

llvm-svn: 210403
diff --git a/clang/lib/Sema/SemaPseudoObject.cpp b/clang/lib/Sema/SemaPseudoObject.cpp
index 19cb12c..eaed1e4 100644
--- a/clang/lib/Sema/SemaPseudoObject.cpp
+++ b/clang/lib/Sema/SemaPseudoObject.cpp
@@ -569,13 +569,11 @@
       assert(setter && "both setter and getter are null - cannot happen");
       IdentifierInfo *setterName = 
         setter->getSelector().getIdentifierInfoForSlot(0);
-      const char *compStr = setterName->getNameStart();
-      compStr += 3;
-      IdentifierInfo *getterName = &S.Context.Idents.get(compStr);
+      IdentifierInfo *getterName =
+          &S.Context.Idents.get(setterName->getName().substr(3));
       GetterSelector = 
         S.PP.getSelectorTable().getNullarySelector(getterName);
       return false;
-
     }
   }