Revert "List implicit operator== after implicit destructors in a vtable."

This reverts commit add2b7e.

Failed "Clang::virtual-compare.cpp" test on the arm builders.
See
http://lab.llvm.org:8011/builders/llvm-clang-win-x-armv7l/builds/3169
for details.

Author: vvereschaka

clang/lib/AST/VTableBuilder.cpp

@@ -1474,11 +1474,11 @@ void ItaniumVTableBuilder::AddMethods(
       llvm_unreachable("Found a duplicate primary base!");
   }
 
+  const CXXDestructorDecl *ImplicitVirtualDtor = nullptr;
+
   typedef llvm::SmallVector<const CXXMethodDecl *, 8> NewVirtualFunctionsTy;
   NewVirtualFunctionsTy NewVirtualFunctions;
 
-  llvm::SmallVector<const CXXMethodDecl*, 4> NewImplicitVirtualFunctions;
-
   // Now go through all virtual member functions and add them.
   for (const auto *MD : RD->methods()) {
     if (!MD->isVirtual())
@@ -1542,30 +1542,24 @@ void ItaniumVTableBuilder::AddMethods(
       }
     }
 
-    if (MD->isImplicit())
-      NewImplicitVirtualFunctions.push_back(MD);
-    else
-      NewVirtualFunctions.push_back(MD);
-  }
-
-  std::stable_sort(
-      NewImplicitVirtualFunctions.begin(), NewImplicitVirtualFunctions.end(),
-      [](const CXXMethodDecl *A, const CXXMethodDecl *B) {
-        if (A->isCopyAssignmentOperator() != B->isCopyAssignmentOperator())
-          return A->isCopyAssignmentOperator();
-        if (A->isMoveAssignmentOperator() != B->isMoveAssignmentOperator())
-          return A->isMoveAssignmentOperator();
-        if (isa<CXXDestructorDecl>(A) != isa<CXXDestructorDecl>(B))
-          return isa<CXXDestructorDecl>(A);
-        assert(A->getOverloadedOperator() == OO_EqualEqual &&
-               B->getOverloadedOperator() == OO_EqualEqual &&
-               "unexpected or duplicate implicit virtual function");
-        // We rely on Sema to have declared the operator== members in the
-        // same order as the corresponding operator<=> members.
-        return false;
-      });
-  NewVirtualFunctions.append(NewImplicitVirtualFunctions.begin(),
-                             NewImplicitVirtualFunctions.end());
+    if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD)) {
+      if (MD->isImplicit()) {
+        // Itanium C++ ABI 2.5.2:
+        //   If a class has an implicitly-defined virtual destructor,
+        //   its entries come after the declared virtual function pointers.
+
+        assert(!ImplicitVirtualDtor &&
+               "Did already see an implicit virtual dtor!");
+        ImplicitVirtualDtor = DD;
+        continue;
+      }
+    }
+
+    NewVirtualFunctions.push_back(MD);
+  }
+
+  if (ImplicitVirtualDtor)
+    NewVirtualFunctions.push_back(ImplicitVirtualDtor);
 
   for (const CXXMethodDecl *MD : NewVirtualFunctions) {
     // Get the final overrider.