OpenACC in Flang

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Intentional deviation from the specification

The end directive for combined construct can omit the loop keyword.
An !$acc routine with no parallelism clause is treated as if the seq clause was present.
!$acc end loop does not trigger a parsing error and is just ignored.
The restriction on !$acc data required clauses is emitted as a portability warning instead of an error as other compiler accepts it.
The if clause accepts scalar integer expression in addition to scalar logical expression.
!$acc routine directive can be placed at the top level.
!$acc cache directive accepts scalar variable.
The !$acc declare directive accepts assumed size array arguments for deviceptr and present clauses.

Array element references in the data clauses are equivalent to array sections consisting of this single element, i.e. copyin(a(n)) is equivalent to copyin(a(n:n)). Some other implementations have treated it as copyin(a(:n)), which does not correspond to OpenACC spec – Flang does not support this interpretation of an array element reference.