Introduce Twine::toStringRef, a variant of toVector which avoids the copy if the

twine can be represented as a single StringRef. Use the new methode to simplify
some twine users.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93317 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Support/Twine.cpp

@@ -15,8 +15,7 @@ using namespace llvm;
 
 std::string Twine::str() const {
   SmallString<256> Vec;
-  toVector(Vec);
-  return std::string(Vec.begin(), Vec.end());
+  return toStringRef(Vec).str();
 }
 
 void Twine::toVector(SmallVectorImpl<char> &Out) const {
@@ -24,6 +23,13 @@ void Twine::toVector(SmallVectorImpl<char> &Out) const {
   print(OS);
 }
 
+StringRef Twine::toStringRef(SmallVectorImpl<char> &Out) const {
+  if (isSingleStringRef())
+    return getSingleStringRef();
+  toVector(Out);
+  return StringRef(Out.data(), Out.size());
+}
+
 void Twine::printOneChild(raw_ostream &OS, const void *Ptr, 
                           NodeKind Kind) const {
   switch (Kind) {