Fix -Wsign-compare warning

llvm-svn: 346515
diff --git a/llvm/lib/IR/Instructions.cpp b/llvm/lib/IR/Instructions.cpp
index 66fdb46..0295da9 100644
--- a/llvm/lib/IR/Instructions.cpp
+++ b/llvm/lib/IR/Instructions.cpp
@@ -1805,7 +1805,7 @@
     return false;
 
   // Must be smaller (else this is an Identity shuffle).
-  if (NumSrcElts <= Mask.size())
+  if (NumSrcElts <= (int)Mask.size())
     return false;
 
   // Find start of extraction, accounting that we may start with an UNDEF.