Add a static_assert about the sizeof(GlobalValue)

I added one for Value back in r262045, and I'm starting to think we
should have these for any class with bitfields whose memory efficiency
really matters.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@290698 91177308-0d34-0410-b5e6-96231b3b80d8

lib/IR/Globals.cpp

@@ -30,6 +30,13 @@ using namespace llvm;
 //                            GlobalValue Class
 //===----------------------------------------------------------------------===//
 
+// GlobalValue should be a Constant, plus a type, a module, some flags, and an
+// intrinsic ID. Add an assert to prevent people from accidentally growing
+// GlobalValue while adding flags.
+static_assert(sizeof(GlobalValue) ==
+                  sizeof(Constant) + 2 * sizeof(void *) + 2 * sizeof(unsigned),
+              "unexpected GlobalValue size growth");
+
 bool GlobalValue::isMaterializable() const {
   if (const Function *F = dyn_cast<Function>(this))
     return F->isMaterializable();