'reduction' has a few restrictions over normal 'var-list' clauses:
1- On parallel, a num_gangs can only have 1 argument when combined with
reduction. These two aren't able to be combined on any other of the
compute constructs however.
2- The vars all must be 'numerical data types' types of some sort, or a
'composite of numerical data types'. A list of types is given in the
standard as a minimum, so we choose 'isScalar', which covers all of
these types and keeps types that are actually numeric. Other compilers
don't seem to implement the 'composite of numerical data types', though
we do.
3- Because of the above restrictions, member-of-composite is not
allowed, so any access via a memberexpr is disallowed. Array-element and
sub-arrays (aka array sections) are both permitted, so long as they meet
the requirements of #2.
This patch implements all of these for compute constructs.
This implementation takes quite a bit from the OMP implementation of
array sections, but only has to enforce the rules as applicable to
OpenACC. Additionally, it does its best to create an AST node (with the
assistance of RecoveryExprs) with as much checking done as soon as
possible in the case of instantiations.
The private clause is the first that takes a 'var-list', thus this has a
lot of additional work to enable the var-list type. A 'var' is a
traditional variable reference, subscript, member-expression, or
array-section, so checking of these is pretty minor.
Note: This ran into some issues with array-sections (aka sub-arrays)
that will be fixed in a follow-up patch.
