[Openmp-dev] LLVM microtask fork for parallel

[Alexandre Eichenberger]

Hi guys,

I saw that you changed the "parallel" handling of the microtask to passing
a pointer to an array of shared variables, which I believe will result in
faster performance.

I noticed that the argc in the __kmpc_fork_call is always 2, but it passes
only 1 additional parameter in the elipsis "...". Is that on purpose?

See the example below

int main()
{
  int d, e;
  float f;
  #pragma omp parallel num_threads(4) shared(d, e, f)
  {
    printf("hi from %d\n", omp_get_thread_num());
  }
  return 1;
}

and clang gen this

  call void ({ i32, i32, i32, i32, i8* }*, i32, void (i32*,
i32*, ...)*, ...)* @__kmpc_fork_call(
	{ i32, i32, i32, i32, i8* }* %.__kmpc_ident_t.2.,    // location
	i32 2,           					// argc
	void (i32*, i32*, ...)* bitcast (void (i32*, i32*, i8*)*
@.omp_microtask. to void (i32*, i32*, ...)*), // microtask
	%struct.anon* %agg.captured) // first and only param in the ... list

It is not a problem, as we will pass a garbage value to the microtask,
which will not be used... but nevertheless, though you may want to know of
this


Alexandre