[clang-tidy][NFC] optimize unused using decls performance (#110200)

Improve performance by moving the check forward to the matching stage

Author: HerrCai0907

clang-tools-extra/clang-tidy/misc/UnusedUsingDeclsCheck.cpp

@@ -25,6 +25,13 @@ AST_MATCHER_P(DeducedTemplateSpecializationType, refsToTemplatedDecl,
   return false;
 }
 
+AST_MATCHER_P(Type, asTagDecl, clang::ast_matchers::internal::Matcher<TagDecl>,
+              DeclMatcher) {
+  if (const TagDecl *ND = Node.getAsTagDecl())
+    return DeclMatcher.matches(*ND, Finder, Builder);
+  return false;
+}
+
 } // namespace
 
 // A function that helps to tell whether a TargetDecl in a UsingDecl will be
@@ -61,7 +68,8 @@ void UnusedUsingDeclsCheck::registerMatchers(MatchFinder *Finder) {
   Finder->addMatcher(userDefinedLiteral().bind("used"), this);
   Finder->addMatcher(
       loc(elaboratedType(unless(hasQualifier(nestedNameSpecifier())),
-                         hasUnqualifiedDesugaredType(type().bind("usedType")))),
+                         hasUnqualifiedDesugaredType(
+                             type(asTagDecl(tagDecl().bind("used")))))),
       this);
   // Cases where we can identify the UsingShadowDecl directly, rather than
   // just its target.
@@ -139,12 +147,6 @@ void UnusedUsingDeclsCheck::check(const MatchFinder::MatchResult &Result) {
     return;
   }
 
-  if (const auto *T = Result.Nodes.getNodeAs<Type>("usedType")) {
-    if (const auto *ND = T->getAsTagDecl())
-      RemoveNamedDecl(ND);
-    return;
-  }
-
   if (const auto *UsedShadow =
           Result.Nodes.getNodeAs<UsingShadowDecl>("usedShadow")) {
     removeFromFoundDecls(UsedShadow->getTargetDecl());