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diff --git a/clang-tools-extra/clang-tidy/performance/UnnecessaryCopyInitializationCheck.h b/clang-tools-extra/clang-tidy/performance/UnnecessaryCopyInitializationCheck.h
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+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_PERFORMANCE_UNNECESSARYCOPYINITIALIZATIONCHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_PERFORMANCE_UNNECESSARYCOPYINITIALIZATIONCHECK_H
+
+#include "../ClangTidyCheck.h"
+#include "clang/AST/Decl.h"
+
+namespace clang::tidy::performance {
+
+// The check detects local variable declarations that are copy initialized with
+// the const reference of a function call or the const reference of a method
+// call whose object is guaranteed to outlive the variable's scope and suggests
+// to use a const reference.
+//
+// The check currently only understands a subset of variables that are
+// guaranteed to outlive the const reference returned, namely: const variables,
+// const references, and const pointers to const.
+//
+// For the user-facing documentation see:
+// https://clang.llvm.org/extra/clang-tidy/checks/performance/unnecessary-copy-initialization.html
+class UnnecessaryCopyInitializationCheck : public ClangTidyCheck {
+public:
+  UnnecessaryCopyInitializationCheck(StringRef Name, ClangTidyContext *Context);
+  bool isLanguageVersionSupported(const LangOptions &LangOpts) const override {
+    return LangOpts.CPlusPlus;
+  }
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+  void storeOptions(ClangTidyOptions::OptionMap &Opts) override;
+
+protected:
+  // A helper to manipulate the state common to
+  // `CopyFromMethodReturn` and `CopyFromLocalVar`.
+  struct CheckContext {
+    const VarDecl &Var;
+    const Stmt &BlockStmt;
+    const DeclStmt &VarDeclStmt;
+    clang::ASTContext &ASTCtx;
+    const bool IssueFix;
+    const bool IsVarUnused;
+    const bool IsVarOnlyUsedAsConst;
+  };
+
+  // Create diagnostics. These are virtual so that derived classes can change
+  // behaviour.
+  virtual void diagnoseCopyFromMethodReturn(const CheckContext &Ctx);
+  virtual void diagnoseCopyFromLocalVar(const CheckContext &Ctx,
+                                        const VarDecl &OldVar);
+
+private:
+  void handleCopyFromMethodReturn(const CheckContext &Ctx,
+                                  const VarDecl *ObjectArg);
+  void handleCopyFromLocalVar(const CheckContext &Ctx, const VarDecl &OldVar);
+
+  void maybeIssueFixes(const CheckContext &Ctx, DiagnosticBuilder &Diagnostic);
+
+  const std::vector<StringRef> AllowedTypes;
+  const std::vector<StringRef> ExcludedContainerTypes;
+};
+
+} // namespace clang::tidy::performance
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_PERFORMANCE_UNNECESSARYCOPYINITIALIZATIONCHECK_H