Fixed deadstoreelimination bug where negative indices were incorrectly causing the optimisation to occur

Turns out long long + unsigned long long is unsigned.  Doh!

Fixes http://llvm.org/bugs/show_bug.cgi?id=11455

llvm-svn: 145731
diff --git a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
index f5688cb..b9b1cc8 100644
--- a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -416,7 +416,7 @@
   // writes to addresses which will definitely be overwritten later
   if (LaterOff > EarlierOff &&
       LaterOff < int64_t(EarlierOff + Earlier.Size) &&
-      LaterOff + Later.Size >= EarlierOff + Earlier.Size)
+      int64_t(LaterOff + Later.Size) >= int64_t(EarlierOff + Earlier.Size))
     return OverwriteEnd;
 
   // Otherwise, they don't completely overlap.