[clang-tools-extra] [clang-tidy] Add performance-move-smart-pointer-contents check. (PR #66139)

[Piotr Zegar via cfe-commits]

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+.. title:: clang-tidy - performance-move-smart-pointer-contents
+
+performance-move-smart-pointer-contents
+=======================================
+
+Given a smart pointer containing a movable type, such as a
+`std::unique_ptr<SomeProtocolBuffer>`, it's possible to move the contents of the
+pointer rather than the pointer itself (ie `std::move(*p)` rather than
+`*std::move(p)`). Doing so is a pessimization, as if the type could be efficiently
+moved we wouldn't need to put it in a `unique_ptr` to begin with.
----------------
PiotrZSL wrote:

"Doing so is a pessimization, as if the type could be efficiently
moved we wouldn't need to put it in a `unique_ptr` to begin with."

You do not know a reasons why someone used unique_ptr, maybe they use custom deleter, maybe they follow some guidelines, maybe they want object to be on heap, not on stack.

https://github.com/llvm/llvm-project/pull/66139