Remove internal use of auto from temp_var_type when creating temporaries
auto
is deprecated as a variable type, but it's used internally whenever
untyped temporaries are created, which leads to suprising DeprecationWarnings.
Switching to None is not ideal, because None is already used in temp_var_type to represent no value.
Hence, this change introduces an "optional" object wrapper to loopy and uses it to represent the absence of a temp_var_type in an assignment instruction.
This change also:
- fixes a deprecated usage in the tutorial
- makes warnings about lp.auto as dtype more informative
Edited by Matt Wala