From a396eb8ae9ab6bebce072255b1c398ab6c95be8d Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Fri, 25 Mar 2005 00:02:41 +0000
Subject: Make the spliceFrom case where one graph is completely empty be
 constant time.

llvm-svn: 20825
---
 llvm/lib/Analysis/DataStructure/DataStructure.cpp | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

(limited to 'llvm/lib/Analysis/DataStructure/DataStructure.cpp')

diff --git a/llvm/lib/Analysis/DataStructure/DataStructure.cpp b/llvm/lib/Analysis/DataStructure/DataStructure.cpp
index 1133743b5d3..6460287ac71 100644
--- a/llvm/lib/Analysis/DataStructure/DataStructure.cpp
+++ b/llvm/lib/Analysis/DataStructure/DataStructure.cpp
@@ -1321,8 +1321,12 @@ void DSGraph::spliceFrom(DSGraph &RHS) {
   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);
-- 
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