[llvm-dev] Spurious cast warning for C++?

[Brennan Vincent via llvm-dev]

How difficult would it be to add a warning to Clang when the programmer
performs a cast that provably has no effect?

A particular case I have in mind is someone getting confused and calling
std::move on an argument to a copy-constructor for a class that doesn't
implement move semantics.

I would be grateful if someone either (1) told me why this is
difficult/impossible, or (2) gave me some pointers to where I could
start trying to implement it...