From 4f155b4c8597f40a79add430dfedb2c08ba28375 Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Fri, 10 Aug 2007 07:02:50 +0000
Subject: [PATCH] memcpy with zero length is hugely expensive, so avoid it. 
 This speeds up coallescing from 1.17s to 0.88s on siod.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@40984 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/ADT/SmallVector.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/llvm/ADT/SmallVector.h b/include/llvm/ADT/SmallVector.h
index 1c970a55981..e6c81a6420c 100644
--- a/include/llvm/ADT/SmallVector.h
+++ b/include/llvm/ADT/SmallVector.h
@@ -380,7 +380,11 @@ SmallVectorImpl<T>::operator=(const SmallVectorImpl<T> &RHS) {
   unsigned CurSize = unsigned(size());
   if (CurSize >= RHSSize) {
     // Assign common elements.
-    iterator NewEnd = std::copy(RHS.Begin, RHS.Begin+RHSSize, Begin);
+    iterator NewEnd;
+    if (RHSSize)
+      NewEnd = std::copy(RHS.Begin, RHS.Begin+RHSSize, Begin);
+    else
+      NewEnd = Begin;
     
     // Destroy excess elements.
     destroy_range(NewEnd, End);