[PATCH] D137205: [clang-tidy] Add performance-unnecessary-copy-on-last-use check

[Fabian Keßler via Phabricator via cfe-commits]

Febbe added a comment.

In D137205#3920016 <https://reviews.llvm.org/D137205#3920016>, @firewave wrote:

> Getting this false positive:
>
>   #include <string>
>   
>   extern std::string str()
>   {
>   	std::string ret;
>   	return ret.empty() ? ret : ret.substr(1);
>   }
>
>
>
>   input.cpp:6:23: warning: Parameter 'ret' is copied on last use, consider moving it instead. [performance-unnecessary-copy-on-last-use]
>           return ret.empty() ? ret : ret.substr(1);
>                                ^
>                                std::move( )
>
> Appears to be caused by the ternary since I also have it inline with a function parameter in another case.

As I know, the compilers can't copy elide always on ternary operators. Therefore, I have also a test, suggesting it on return.



================
Comment at: clang-tools-extra/docs/clang-tidy/checks/performance/unnecessary-copy-on-last-use.rst:50
+
+   A string specifying which include-style is used, `llvm` or `google`. Default
+   is `llvm`.
----------------
Eugene.Zelenko wrote:
> Could such option be shared between different checks? Or even rely on `.clang-format`?
I just oriented myself at other similar checks, which introduced this. It uses both there:

```
UnnecessaryCopyOnLastUseCheck::UnnecessaryCopyOnLastUseCheck(
    StringRef Name, ClangTidyContext *Context)
    : ClangTidyCheck(Name, Context),
      Inserter(Options.getLocalOrGlobal("IncludeStyle",
                                        utils::IncludeSorter::IS_LLVM),
```

Do you mean, that I can just remove the description of the option, because it is taken from global options?


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D137205/new/

https://reviews.llvm.org/D137205