[clang-tools-extra] [clang-tidy] Speed up deduplicating warnings from alias checks (PR #174237)

[Baranov Victor via cfe-commits]

================
@@ -778,43 +776,35 @@ std::vector<ClangTidyError> ClangTidyDiagnosticConsumer::take() {
 
   llvm::stable_sort(Errors, LessClangTidyError());
   Errors.erase(llvm::unique(Errors, EqualClangTidyError()), Errors.end());
-  if (RemoveIncompatibleErrors)
+  if (RemoveIncompatibleErrors) {
+    removeDuplicatedDiagnosticsOfAliasCheckers();
     removeIncompatibleErrors();
+  }
   return std::move(Errors);
 }
 
-namespace {
-struct LessClangTidyErrorWithoutDiagnosticName {
-  bool operator()(const ClangTidyError *LHS, const ClangTidyError *RHS) const {
-    const tooling::DiagnosticMessage &M1 = LHS->Message;
-    const tooling::DiagnosticMessage &M2 = RHS->Message;
-
-    return std::tie(M1.FilePath, M1.FileOffset, M1.Message) <
-           std::tie(M2.FilePath, M2.FileOffset, M2.Message);
-  }
-};
-} // end anonymous namespace
-
 void ClangTidyDiagnosticConsumer::removeDuplicatedDiagnosticsOfAliasCheckers() {
-  using UniqueErrorSet =
-      std::set<ClangTidyError *, LessClangTidyErrorWithoutDiagnosticName>;
-  UniqueErrorSet UniqueErrors;
+  if (Errors.size() <= 1)
+    return;
 
-  auto IT = Errors.begin();
-  while (IT != Errors.end()) {
-    ClangTidyError &Error = *IT;
-    const std::pair<UniqueErrorSet::iterator, bool> Inserted =
-        UniqueErrors.insert(&Error);
+  static constexpr auto Projection = [](const ClangTidyError &E) {
+    const tooling::DiagnosticMessage &M = E.Message;
+    return std::tie(M.FilePath, M.FileOffset, M.Message);
+  };
 
+  auto LastUniqueError = Errors.begin();
----------------
vbvictor wrote:

```suggestion
  auto LastUniqueErrorIt = Errors.begin();
```

https://github.com/llvm/llvm-project/pull/174237