Use back() instead of [size()-1].

llvm-svn: 52600
diff --git a/llvm/lib/CodeGen/DwarfWriter.cpp b/llvm/lib/CodeGen/DwarfWriter.cpp
index 784bf93..086786b 100644
--- a/llvm/lib/CodeGen/DwarfWriter.cpp
+++ b/llvm/lib/CodeGen/DwarfWriter.cpp
@@ -3304,7 +3304,7 @@
 
           // Try to merge with the previous call-site.
           if (PreviousIsInvoke) {
-            CallSiteEntry &Prev = CallSites[CallSites.size()-1];
+            CallSiteEntry &Prev = CallSites.back();
             if (Site.PadLabel == Prev.PadLabel && Site.Action == Prev.Action) {
               // Extend the range of the previous entry.
               Prev.EndLabel = Site.EndLabel;