[flang][doc] Added remark about array element references in data clauses.

[vzakhari]

…ses.

[llvmbot]

@llvm/pr-subscribers-openacc

Author: Slava Zakharin (vzakhari)

Changes

…ses.

---

Full diff: https://github.com/llvm/llvm-project/pull/72332.diff

1 Files Affected:

• (modified) flang/docs/OpenACC.md (+7)

diff --git a/flang/docs/OpenACC.md b/flang/docs/OpenACC.md
index 4c36a38f8bf5731..9be6ee2ff4e7832 100644
--- a/flang/docs/OpenACC.md
+++ b/flang/docs/OpenACC.md
@@ -25,3 +25,10 @@ local:
   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.

[razvanlupusoru]

Thank you for adding this remark!

[clementval]

Shouldn't we use the parenthesis notation instead of brackets for Fortran?

[vzakhari]

Thanks for the catch!