offload/test/offloading/strided_update/strided_update_ptr_partial_to.c

// This test checks that #pragma omp target update to(data[0:2:3]) correctly
// updates every third element (stride 3) from the host to the device, partially
// across the array using dynamically allocated memory.

// RUN: %libomptarget-compile-run-and-check-generic
#include <omp.h>
#include <stdio.h>
#include <stdlib.h>

int main() {
  int len = 11;
  double *data = (double *)calloc(len, sizeof(double));

  // Initialize on host
  for (int i = 0; i < len; i++)
    data[i] = i;

  // Initial values
  printf("original host array values:\n");
  for (int i = 0; i < len; i++)
    printf("%f\n", data[i]);
  printf("\n");

#pragma omp target data map(tofrom : data[0 : len])
  {
// Initialize device array to 20
#pragma omp target
    {
      for (int i = 0; i < len; i++)
        data[i] = 20.0;
    }

    // Modify host data for elements that will be updated
    data[0] = 10.0;
    data[3] = 10.0;

// This creates Host→Device transfer for indices 0,3 only
#pragma omp target update to(data[0 : 2 : 3])

// Verify on device by adding 5 to all elements
#pragma omp target
    {
      for (int i = 0; i < len; i++)
        data[i] += 5.0;
    }
  }

  printf("device array values after update to:\n");
  for (int i = 0; i < len; i++)
    printf("%f\n", data[i]);
  printf("\n");

  // CHECK: original host array values:
  // CHECK-NEXT: 0.000000
  // CHECK-NEXT: 1.000000
  // CHECK-NEXT: 2.000000
  // CHECK-NEXT: 3.000000
  // CHECK-NEXT: 4.000000
  // CHECK-NEXT: 5.000000
  // CHECK-NEXT: 6.000000
  // CHECK-NEXT: 7.000000
  // CHECK-NEXT: 8.000000
  // CHECK-NEXT: 9.000000
  // CHECK-NEXT: 10.000000

  // CHECK: device array values after update to:
  // CHECK-NEXT: 15.000000
  // CHECK-NEXT: 25.000000
  // CHECK-NEXT: 25.000000
  // CHECK-NEXT: 15.000000
  // CHECK-NEXT: 25.000000
  // CHECK-NEXT: 25.000000
  // CHECK-NEXT: 25.000000
  // CHECK-NEXT: 25.000000
  // CHECK-NEXT: 25.000000
  // CHECK-NEXT: 25.000000
  // CHECK-NEXT: 25.000000

  free(data);
  return 0;
}