https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68960
Bug ID: 68960
Summary: __attribute__ ((aligned ())) is ignored for OpenMP
private variables
Product: gcc
Version: 4.8.4
Status: UNCONFIRMED
Severity: major
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: dxin at usc dot edu
Target Milestone: ---
Test code:
#include <stdio.h>
int main(void)
{
int temp[4][4] __attribute__ ((aligned (256)))={{0}};
//#pragma omp for private(temp)
for(size_t i=0; i<4;i++){
printf("chunk %zu: &temp[0][0]=%p\n", i, &temp[0][0]);
}
return 0;
}
Without OpenMP, alignment is correctly set to 256 bytes:
gcc main.c -fopenmp -std=gnu11
./a.out
chunk 0: &temp[0][0]=0x7ffffbe0ef00
chunk 1: &temp[0][0]=0x7ffffbe0ef00
chunk 2: &temp[0][0]=0x7ffffbe0ef00
chunk 3: &temp[0][0]=0x7ffffbe0ef00
With OpenMP, alignment is default 16 bytes:
gcc main.c -fopenmp -std=gnu11
./a.out
chunk 0: &temp[0][0]=0x7fff16c56ac0
chunk 1: &temp[0][0]=0x7fff16c56ac0
chunk 2: &temp[0][0]=0x7fff16c56ac0
chunk 3: &temp[0][0]=0x7fff16c56ac0
Tested with:
gcc (Ubuntu 4.8.4-2ubuntu1~14.04) 4.8.4, on x86-64
gcc (Ubuntu/Linaro 4.8.4-2ubuntu1~14.04) 4.8.4, on arm v7
