[clang][AST][NFC] Factor out check for structural equivalence of names.

[davidstone]

Summary

We have four places that we try to decide which name to use for the test for structural equivalence, and in each of those we evaluate getTypedefNameForAnonDecl twice. Pull out the check into a function to reduce duplication and evaluate things only once.

[aaron.ballman]

LGTM! I'll fix up the nits when I land on your behalf.

clang/lib/AST/ASTStructuralEquivalence.cpp

1456–1467

Minor nits for our weird coding style.

clang/lib/AST/ASTStructuralEquivalence.cpp

while (true) {
 
     DC1 = DC1->getParent()->getNonTransparentContext();
     DC2 = DC2->getParent()->getNonTransparentContext();
   }
 
   return true;
 }
 
+static bool NameIsStructurallyEquivalent(const TagDecl &D1, const TagDecl &D2) {
+  auto GetName = [](const TagDecl &D) -> const IdentifierInfo * {
+    if (const IdentifierInfo *Name = D.getIdentifier())
+      return Name;
+    if (const TypedefNameDecl *TypedefName = D.getTypedefNameForAnonDecl())
+      return TypedefName->getIdentifier();
+    return nullptr;
+  };
+  return IsStructurallyEquivalent(GetName(D1), GetName(D2));
+}
+
 /// Determine structural equivalence of two records.
 static bool IsStructurallyEquivalent(StructuralEquivalenceContext &Context,
                                      RecordDecl *D1, RecordDecl *D2) {
-
-  // Check for equivalent structure names.
-  IdentifierInfo *Name1 = D1->getIdentifier();
-  if (!Name1 && D1->getTypedefNameForAnonDecl())
-    Name1 = D1->getTypedefNameForAnonDecl()->getIdentifier();
-  IdentifierInfo *Name2 = D2->getIdentifier();
-  if (!Name2 && D2->getTypedefNameForAnonDecl())
-    Name2 = D2->getTypedefNameForAnonDecl()->getIdentifier();
-  if (!IsStructurallyEquivalent(Name1, Name2))
+  if (!NameIsStructurallyEquivalent(*D1, *D2)) {
     return false;
+  }
 
   if (D1->isUnion() != D2->isUnion()) {
     if (Context.Complain) {
       Context.Diag2(D2->getLocation(), Context.getApplicableDiagnostic(
                                            diag::err_odr_tag_type_inconsistent))
           << Context.ToCtx.getTypeDeclType(D2);
       Context.Diag1(D1->getLocation(), diag::note_odr_tag_kind_here)
           << D1->getDeclName() << (unsigned)D1->getTagKind();
static bool IsStructurallyEquivalent(StructuralEquivalenceContext &Context,
   // Init expressions are the most expensive check, so do them last.
   return IsStructurallyEquivalent(Context, D1->getInitExpr(),
                                   D2->getInitExpr());
 }
 
 /// Determine structural equivalence of two enums.
 static bool IsStructurallyEquivalent(StructuralEquivalenceContext &Context,
                                      EnumDecl *D1, EnumDecl *D2) {
-
-  // Check for equivalent enum names.
-  IdentifierInfo *Name1 = D1->getIdentifier();
-  if (!Name1 && D1->getTypedefNameForAnonDecl())
-    Name1 = D1->getTypedefNameForAnonDecl()->getIdentifier();
-  IdentifierInfo *Name2 = D2->getIdentifier();
-  if (!Name2 && D2->getTypedefNameForAnonDecl())
-    Name2 = D2->getTypedefNameForAnonDecl()->getIdentifier();
-  if (!IsStructurallyEquivalent(Name1, Name2))
+  if (!NameIsStructurallyEquivalent(*D1, *D2)) {
     return false;
+  }
 
   // Compare the definitions of these two enums. If either or both are
   // incomplete (i.e. forward declared), we assume that they are equivalent.
   D1 = D1->getDefinition();
   D2 = D2->getDefinition();
   if (!D1 || !D2)
     return true;