2e353a635b
OpenACC declare statements are restricted from having having clauses
that reference assumed size arrays. It should be the case that we can
implement `deviceptr` and `present` clauses for assumed-size arrays.
This is a first step towards relaxing this restriction.
Note running flang on the following example results in an error in
lowering.
```
$ cat t.f90
subroutine vadd (a, b, c, n)
real(8) :: a(*), b(*), c(*)
!$acc declare deviceptr(a, b, c)
!$acc parallel loop
do i = 1,n
c(i) = a(i) + b(i)
enddo
end subroutine
$ flang -fopenacc -c t.f90
error: loc("/home/akuhlenschmi/work/p4/ta/tests/openacc/src/t.f90":3:7): expect declare attribute on variable in declare operation
error: Lowering to LLVM IR failed
error: loc("/home/akuhlenschmi/work/p4/ta/tests/openacc/src/t.f90":4:7): unsupported OpenACC operation: acc.private.recipe
error: loc("/home/akuhlenschmi/work/p4/ta/tests/openacc/src/t.f90":4:7): LLVM Translation failed for operation: acc.private.recipe
error: failed to create the LLVM module
```
I would like to to share this code, because others are currently working
on the implementation of `deviceptr`, but it is obviously not running
end-to-end. I think the cleanest approach to this would be to put this
exception to the rule behind some feature flag, but I am not certain
what the precedence for that is.
1.4 KiB
1.4 KiB
OpenACC in Flang
---
local:
---
Intentional deviation from the specification
- The end directive for combined construct can omit the
loopkeyword. - An
!$acc routinewith no parallelism clause is treated as if theseqclause was present. !$acc end loopdoes not trigger a parsing error and is just ignored.- The restriction on
!$acc datarequired clauses is emitted as a portability warning instead of an error as other compiler accepts it. - The
ifclause accepts scalar integer expression in addition to scalar logical expression. !$acc routinedirective can be placed at the top level.!$acc cachedirective accepts scalar variable.- The
!$acc declaredirective accepts assumed size array arguments fordeviceptrandpresentclauses.
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 tocopyin(a(n:n)). Some other implementations have treated it ascopyin(a(:n)), which does not correspond to OpenACC spec – Flang does not support this interpretation of an array element reference.