[DwarfDebug][NFC] Factor out 'isInitialized' logic

[fdeazeve]

Summary

The class 'DbgVariable' can be in one of three states, and the "is any of them
initialized" logic for them is repeated in a couple of places. We may want to
expand this class in the future; as such, we factor out this common logic so
that it is easier to modify.

[aprantl]

I wonder if these should all be constructors or static ::create() methods?

[fdeazeve]

In D158438#4604065, @aprantl wrote:

I wonder if these should all be constructors or static ::create() methods?

I very much want to address this if we decide to split this class!

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h

 public:
   /// Construct a DbgVariable.
   ///
   /// Creates a variable without any DW_AT_location.  Call \a initializeMMI()
   /// for MMI entries, or \a initializeDbgValue() for DBG_VALUE instructions.
   DbgVariable(const DILocalVariable *V, const DILocation *IA)
       : DbgEntity(V, IA, DbgVariableKind) {}
 
+  bool isInitialized() const {
+    return !FrameIndexExprs.empty() || ValueLoc;
+  }
+
   /// Initialize from the MMI table.
   void initializeMMI(const DIExpression *E, int FI) {
-    assert(FrameIndexExprs.empty() && "Already initialized?");
-    assert(!ValueLoc.get() && "Already initialized?");
+    assert(!isInitialized() && "Already initialized?");
 
     assert((!E || E->isValid()) && "Expected valid expression");
     assert(FI != std::numeric_limits<int>::max() && "Expected valid index");
 
     FrameIndexExprs.push_back({FI, E});
   }
 
   // Initialize variable's location.
   void initializeDbgValue(DbgValueLoc Value) {
-    assert(FrameIndexExprs.empty() && "Already initialized?");
-    assert(!ValueLoc && "Already initialized?");
+    assert(!isInitialized() && "Already initialized?");
     assert(!Value.getExpression()->isFragment() && "Fragments not supported.");
 
     ValueLoc = std::make_unique<DbgValueLoc>(Value);
     if (auto *E = ValueLoc->getExpression())
       if (E->getNumElements())
         FrameIndexExprs.push_back({0, E});
   }