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

The class 'DbgVariable' can be in one of three states, and the "is any of them
initialization" 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.

Differential Revision: https://reviews.llvm.org/D158438

(cherry picked from commit 3222312)

Author: felipepiovezan

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.h

@@ -136,10 +136,13 @@ class DbgVariable : public DbgEntity {
   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");
@@ -149,8 +152,7 @@ class DbgVariable : public DbgEntity {
 
   // 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);