OpenACC in Flang
Intentional deviation from the specification
- The end directive for combined construct can omit the
!$acc routine with no parallelism clause is treated as if the
seq clause was present.
!$acc end loop does not trigger a parsing error and is just ignored.
- The restriction on
!$acc data required clauses is emitted as a portability warning instead of an error as other compiler accepts it.
if clause accepts scalar integer expression in addition to scalar logical expression.
!$acc routine directive can be placed at the top level.
!$acc cache directive accepts scalar variable.
Remarks about incompatibilities with other implementations
- 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.