Commits on Nov 9, 2021

1. Re-enable copy[_nonoverlapping]() runtime checks …

   This commit re-enables the debug checks for valid usages of the two
   functions `copy()` and `copy_nonoverlapping()`. Those checks were com-
   mented out in rust-lang#79684 in order to make the functions const. All that's
   been left was a FIXME, that could not be resolved until there is was way
   to only do the checks at runtime.
   Since rust-lang#89247 there is such a way: `const_eval_select()`. This commit
   uses that new intrinsic in order to either do nothing (at compile time)
   or to do the old checks (at runtime).
   
   The change itself is rather small: in order to make the checks usable
   with `const_eval_select`, they are moved into a local function (one for
   `copy` and one for `copy_nonoverlapping` to keep symmetry).
   
   The change does not break referential transparency, as there is nothing
   you can do at compile time, which you cannot do on runtime without get-
   ting undefined behavior. The CTFE-engine won't allow missuses. The other
   way round is also fine.

   

   jfrimmel committed Nov 9, 2021
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