Add a fast path for setName("") on an unnamed value.

llvm-svn: 79492

llvm/include/llvm/ADT/Twine.h

@@ -320,6 +320,16 @@ namespace llvm {
       return Twine(&Val, UHexKind, 0, EmptyKind);
     }
 
+    /// @}
+    /// @name Predicate Operations
+    /// @{
+
+    /// isTriviallyEmpty - Check if this twine is trivially empty; a false
+    /// return value does not necessarily mean the twine is empty.
+    bool isTriviallyEmpty() const {
+      return isNullary();
+    }
+
     /// @}
     /// @name String Operations
     /// @{

llvm/lib/VMCore/Value.cpp

@@ -171,6 +171,10 @@ std::string Value::getNameStr() const {
 }
 
 void Value::setName(const Twine &NewName) {
+  // Fast path for common IRBuilder case of setName("") when there is no name.
+  if (NewName.isTriviallyEmpty() && !hasName())
+    return;
+
   SmallString<256> NameData;
   NewName.toVector(NameData);