Handling declare target

[yanyh15]

The declare directive, e.g. declare target, impacts the lowering of the code in the later stage, thus needs to handled at the very beginning before the lowering.

Declare target indicates to put device for a symbol (variable or function) to make it as a device-side-only symbol. Thus the symbol should not be applied default mapping when the compiler analyze symbols to apply default mapping. To do this, all the symbols of the declare target need to be inserted in the symbol table as global first for the file that will be produced by lowering for the kernel.

[ouankou]

declare target creates two copies of declared symbols.
Given the following code:

#include <stdio.h>

#pragma omp declare target
int x = 100;
#pragma omp end declare target

int main(int argc, char **argv) {

  printf("On host: x = %d\n", x); // output: x = 100

#pragma omp target
  {
    x = 200;
    printf("On device: x = %d\n", x); // output: x = 200
  }

  printf("On host: x = %d\n", x); // output: x = 100
  x = 300;

#pragma omp target
  { printf("On device: x = %d\n", x); } // output: x = 200

  return 0;
}