Make the spliceFrom case where one graph is completely empty be constant time.
llvm-svn: 20825
diff --git a/llvm/lib/Analysis/DataStructure/DataStructure.cpp b/llvm/lib/Analysis/DataStructure/DataStructure.cpp
index 1133743..6460287 100644
--- a/llvm/lib/Analysis/DataStructure/DataStructure.cpp
+++ b/llvm/lib/Analysis/DataStructure/DataStructure.cpp
@@ -1321,8 +1321,12 @@
AuxFunctionCalls.splice(AuxFunctionCalls.end(), RHS.AuxFunctionCalls);
// Take all of the return nodes.
- ReturnNodes.insert(RHS.ReturnNodes.begin(), RHS.ReturnNodes.end());
- RHS.ReturnNodes.clear();
+ if (ReturnNodes.empty()) {
+ ReturnNodes.swap(RHS.ReturnNodes);
+ } else {
+ ReturnNodes.insert(RHS.ReturnNodes.begin(), RHS.ReturnNodes.end());
+ RHS.ReturnNodes.clear();
+ }
// Merge the scalar map in.
ScalarMap.spliceFrom(RHS.ScalarMap);