https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106662
Bug ID: 106662
Summary: [OpenMP] 'for simd firstprivate(j) lastprivate(j)'
with 'parallel shared(j)' gives unexpected result
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Keywords: openmp, wrong-code
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: burnus at gcc dot gnu.org
CC: jakub at gcc dot gnu.org, sandra at gcc dot gnu.org
Target Milestone: ---
[Lightly related to PR106504 - but that one uses 'parallel private' not
shared.]
The following program, converted to C++ from libgomp.fortran/pr27416-1.f90
and with 'simd' added to the workshare-loop construct,
yields:
* 22 with 'for' - i.e. the existing Fortran testcase, but C++-ified.
and independent of 'num_threads(1)'
* 22 with clang++-12
* 22 with icc 19
while
* 16 is obtained with GCC
(as if 0 and not 6 is firstprivatized)
int
main()
{
int j = 6;
#pragma omp parallel num_threads (4) shared(j)
{
int i;
#pragma omp for simd firstprivate (j) lastprivate (j) // private(i)
for (i = 1; i <= 16; ++i)
if (i == 16)
j = j + i;
}
__builtin_printf("j = %i =?= %i\n", j, 6+16);
if (j != 6+16)
__builtin_abort();
return 0;
}
Likewise with a combined construct:
...
#pragma omp parallel for simd num_threads (4) firstprivate (j) lastprivate
(j)
for (int i = 1; i <= 16; ++i)
...
And likewise with the equivalent Fortran code.
