ADT/STLExtras: Introduce llvm::empty; NFC

This is modeled after C++17 std::empty().

Differential Revision: https://reviews.llvm.org/D53909

llvm-svn: 345679
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index dd0d441..849f9ee 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -5260,7 +5260,7 @@
 
   // Figure out the corresponding result for each case value and phi node in the
   // common destination, as well as the min and max case values.
-  assert(SI->case_begin() != SI->case_end());
+  assert(!empty(SI->cases()));
   SwitchInst::CaseIt CI = SI->case_begin();
   ConstantInt *MinCaseVal = CI->getCaseValue();
   ConstantInt *MaxCaseVal = CI->getCaseValue();