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<!--===- docs/Extensions.md
Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
See https://llvm.org/LICENSE.txt for license information.
SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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# OpenACC in Flang
```{contents}
---
local:
---
```
## 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.
* The OpenACC specification disallows a variable appearing multiple times in
clauses of `!$acc declare` directives for a function, subroutine, program,
or module, but it is allowed with a warning when same clause is used.
## 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.
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