The present test will be looking if "a" is on the device. Hence, when the second data region is encountered, "a" is already on the device but only partially. Instead, a better method would be to add a pointer to point into "a" and reference this pointer on the device. Something like:
#include <stdio.h>
int main () {
int a[200];
int *b;
int i;
for(i=0; i<200; i++) a[i] = 0;
b=a+100;
#pragma acc data pcopy(a[0:20])
{
#pragma acc data pcopy(b[0:20])
{
#pragma acc parallel loop
for(i=0; i<20; i++) {
a[i] = i;
b[i] = i;
}
}
}
for(i=0; i<22; i++) printf("%d = %d \n", i, a[i]);
for(i=100; i<122; i++) printf("%d = %d \n", i, a[i]);
return 0;
}
If you had just copied "a[100:20]", then accessing outside this range would be considered a programmer error.
Hope this helps, Mat