[clang-tools-extra] [clang-tidy] Add check performance-lost-std-move (PR #139525)

[Vasiliy Kulikov via cfe-commits]

================
@@ -0,0 +1,47 @@
+.. title:: clang-tidy - performance-lost-std-move
+
+performance-lost-std-move
+=========================
+
+Warns if copy constructor is used instead of ``std::move()`` and suggests a fix.
+It honours cycles, lambdas, and unspecified call order in compound expressions.
+
+.. code-block:: c++
+
+   void f(X);
+
+   void g(X x) {
+     f(x);  // warning: Could be std::move() [performance-lost-std-move]
+   }
+
+It finds the last local variable usage, and if it is a copy, emits a warning.
+The check is based on pure AST matching and doesn't take into account any
+data flow information. Thus, it doesn't catch assign-after-copy cases.
+
+Also it does notice variable references "behind the scenes":
+
+.. code-block:: c++
+
+   void f(X);
+
+   void g(X x) {
+     auto &y = x;
+     f(x);  // does not emit a warning
+     y.f();  // because is still used
+   }
+
+If you want to ignore assigns to reference variables, set ``StrictMode``
+to ``false``.
+
+
+Options
+-------
+
+.. option:: StrictMode
+
+   A variable X can be referenced by another variable R. In this case the last
+   variable usage might be not from X, but from R. It is quite difficult to
+   find in a large function, so if the plugin sees some R references X, then
+   it will not emit a warning for X not to provoke false positive. If you're
+   sure that such references don't extend X' lifetime and ready to handle possible
+   false positives, then set StrictMode to false.
----------------
segoon wrote:

@vbvictor has another opinion. I have no strong opinion based on documentation yet.

https://github.com/llvm/llvm-project/pull/139525