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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@79492 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 14 insertions, 0 deletions

diff --git a/include/llvm/ADT/Twine.h b/include/llvm/ADT/Twine.h
index 2c6ba0bc23..88fde0a54a 100644
--- a/include/llvm/ADT/Twine.h
+++ b/include/llvm/ADT/Twine.h
@@ -321,6 +321,16 @@ namespace llvm {
     }
 
     /// @}
+    /// @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
     /// @{
 
diff --git a/lib/VMCore/Value.cpp b/lib/VMCore/Value.cpp
index 157245d9ea..34291b9d72 100644
--- a/lib/VMCore/Value.cpp
+++ b/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);