openmp-use-default-none

Finds OpenMP directives that are allowed to contain a default clause, but either don't specify it or the clause is specified but with the kind other than none, and suggests to use the default(none) clause.

Using default(none) clause forces developers to explicitly specify data sharing attributes for the variables referenced in the construct, thus making it obvious which variables are referenced, and what is their data sharing attribute, thus increasing readability and possibly making errors easier to spot.

Example

// ``for`` directive can not have ``default`` clause, no diagnostics.
void n0(const int a) {
#pragma omp for
  for (int b = 0; b < a; b++)
    ;
}

// ``parallel`` directive.

// ``parallel`` directive can have ``default`` clause, but said clause is not
// specified, diagnosed.
void p0_0() {
#pragma omp parallel
  ;
  // WARNING: OpenMP directive ``parallel`` does not specify ``default``
  //          clause. Consider specifying ``default(none)`` clause.
}

// ``parallel`` directive can have ``default`` clause, and said clause is
// specified, with ``none`` kind, all good.
void p0_1() {
#pragma omp parallel default(none)
  ;
}

// ``parallel`` directive can have ``default`` clause, and said clause is
// specified, but with ``shared`` kind, which is not ``none``, diagnose.
void p0_2() {
#pragma omp parallel default(shared)
  ;
  // WARNING: OpenMP directive ``parallel`` specifies ``default(shared)``
  //          clause. Consider using ``default(none)`` clause instead.
}