# Extra Clang Tools 21.1.8 documentation

## clang-tidy - altera-single-work-item-barrier

# altera-single-work-item-barrier

Finds OpenCL kernel functions that call a barrier function but do not call an ID function (`get_local_id`, `get_local_id`, `get_group_id`, or `get_local_linear_id`).

These kernels may be viable single work-item kernels, but will be forced to execute as NDRange kernels if using a newer version of the Altera Offline Compiler (>= v17.01).

If using an older version of the Altera Offline Compiler, these kernel functions will be treated as single work-item kernels, which could be inefficient or lead to errors if NDRange semantics were intended.

Based on the Altera SDK for OpenCL: Best Practices Guide.

Examples:

    // error: function calls barrier but does not call an ID function.
    void __kernel barrier_no_id(__global int * foo, int size) {
      for (int i = 0; i < 100; i++) {
        foo[i] += 5;
      }
      barrier(CLK_GLOBAL_MEM_FENCE);
    }

    // ok: function calls barrier and an ID function.
    void __kernel barrier_with_id(__global int * foo, int size) {
      for (int i = 0; i < 100; i++) {
        int tid = get_global_id(0);
        foo[tid] += 5;
      }
      barrier(CLK_GLOBAL_MEM_FENCE);
    }

    // ok with AOC Version 17.01: the reqd_work_group_size turns this into
    // an NDRange.
    __attribute__((reqd_work_group_size(2,2,2)))
    void __kernel barrier_with_id(__global int * foo, int size) {
      for (int i = 0; i < 100; i++) {
        foo[tid] += 5;
      }
      barrier(CLK_GLOBAL_MEM_FENCE);
    }

## Options

AOCVersion

  Defines the version of the Altera Offline Compiler. Defaults to `1600` (corresponding to version 16.00).