https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103385
Bug ID: 103385
Summary: [OpenMP] reduction(+: temp[0], temp[1]) rejected with
'appears more than once'
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Keywords: openmp, rejects-valid
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: burnus at gcc dot gnu.org
Target Milestone: ---
Found via
https://github.com/SOLLVE/sollve_vv/blob/ae54ca3b15a7820125175a1ac478235d20a286b5/tests/5.0/parallel_reduction/test_parallel_reduction_multiple_array_elements.c
(of Pull Request 362)
Ignoring the odd expectation in the linked testcase that there is only a single
thread (and thus expecting temps[0] == 1), it seems as if
static double temps[2];
...
#pragma omp parallel reduction(+:temps[0], temps[1])
{
temps[0] += 1;
temps[1] += 1;
}
is valid. Still, GCC rejects it with
error: ‘temps’ appears more than once in data clauses
At least, the OpenMP specification has the restriction (in OpenMP 5.2, "5.5.5
Properties Common to All Reduction Clauses", [132:11-16]):
Restrictions common to reduction clauses are as follows:
• Any array element must be specified at most once in all list items on a
directive.
[...]
• If a list item is an array section, it must specify contiguous storage, it
cannot be
a zero-length array section and its base expression must be a base language
identifier.
The first bullet implies that 'temp' can appear multiple times – only the
element 0 and 1 may only appear once.
