https://bugs.erlang.org/browse/ERL-851

There would be a bogus warning when compiling the following
function with the `tuple_calls` option:

    dispatch(X) ->
        (list_to_atom("prefix_" ++ atom_to_list(suffix))):doit(X).

The warning would look like this:

    no_file: this expression will fail with a 'badarg' exception

https://bugs.erlang.org/browse/ERL-838

* bjorn/compiler/beam_type/ERL_829/OTP-15518:
  beam_type: Eliminate compiler crash when arithmetic expression fails

* maint-21:
  Updated OTP version
  Prepare release

The compiler would crash when compiling code such as:

     (A / B) band 16#ff

The type for the expression would be 'none', but beam_type:verified_type/1
did not handle 'none'.

https://bugs.erlang.org/browse/ERL-829

* bjorn/compiler/interim-tuple-bug/OTP-15501/ERL-807:
  Remove unsafe optimization for delaying creation of stackframe

b89044a800c4 introduced an optimization that tries to delay creation
of stack frames. It turns out that this optimization is not always
safe. (See the new test case for an example.)

Since the code generator is completely rewritten in the `master`
branch for the upcoming OTP 22 release, it does not make sense trying
to mend this optimization. It is better to remove it.  Out of a sample
of about 1000 modules in OTP, about 50 of them are changed as a result
of removing this optimization.

The compiler in OTP 22 will do the same optimization in a cleaner,
safer, and more effective way.

https://bugs.erlang.org/browse/ERL-807