flang/docs/OpenACC.md

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# OpenACC in Flang


## Intentional deviation from the specification

See [OpenACC-extensions.md](OpenACC-extensions.md) for the full list of
extensions supported by Flang. Flang also adds the following restrictions:

* The OpenACC specification does not prohibit the same variable from appearing
  in multiple data clauses, but this is disallowed for variables appearing in
  `reduction` clauses.
* The OpenACC specification does not prohibit the same variable from appearing
  multiple times in a `use_device` clause on a `host_data` construct, but this
  is disallowed.

## 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.