https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118909
Bug ID: 118909
Summary: OpenMP reduction array is always allocated on stack,
cause stack overflow with large array reduction.
Product: gcc
Version: 14.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libgomp
Assignee: unassigned at gcc dot gnu.org
Reporter: z00823823 at outlook dot com
CC: jakub at gcc dot gnu.org
Target Milestone: ---
Dear maintainer:
The openmp always alloc the recution array on stack, cause stack overflow with
large array. Here is an example:
```c
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main() {
double *test = NULL;
for (size_t size = 1;; size += 1024) {
test = malloc(size * sizeof(double));
if (test == NULL) {
printf("Failed to allocate %zu doubles\n", size);
break;
}
printf("test: %p\n", test);
#pragma omp parallel reduction(+ : test[0 : size]) num_threads(2)
{
test[0] = 0;
#pragma omp critical
{
printf("frame address: %p\n", __builtin_frame_address(0));
printf("test: %p\n", test);
}
}
free(test);
printf("Allocated %zu doubles\n\n", size);
}
}
```
Run it for a while until it crashs. On my laptop it crashs with size > 1046529
(approximately 8MB).
An online version can be found here: https://godbolt.org/z/v1o6K9a1b
