[PATCH] D102175: [clang-tidy] performance-unnecessary-copy-initialization: Remove the complete statement when the copied variable is unused.

[Felix Berger via Phabricator via cfe-commits]

flx added a comment.

In D102175#2759945 <https://reviews.llvm.org/D102175#2759945>, @ymandel wrote:

> Hi Felix,
> Can you clarify your concern over the warning? Is it the case that the warning is not present before the fix and is only triggered after the fix?  I'm concerned that removing the call may have unintended side effects and I would think it might better to leave the check for usage separate.  However, if the fix is causing the warning then I can understand better why you want to make this change.  That said, have considered replacing the var binding with `(void)`, rather than deleting the statement?

Yes, the fix of converting the copied variable to a const reference introduces a warning when -Wall (or more specifically -Wunused) is specified and the variable is not used at all. The fix converts the local variable to a const reference. Take a const reference of an object and not using it has no observable side effects I think.

Here is an example of an unused, but copied variable before the fix:

https://godbolt.org/z/a5E4fMWKj

The compiler flags are "-Werror -Wall": no warnings or errors are produced.

Now after the fix:

https://godbolt.org/z/a5E4fMWKj

For more context, the assumption the check makes is that the copy is unnecessary. If the type executes specific side-effects in its copy-constructor code the type should be excluded from the check using the `AllowedTypes` setting.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D102175/new/

https://reviews.llvm.org/D102175