Amittai Aviram <amittai.aviram@xxxxxxxx> writes:
> Hi! The array omp_clause_num_ops, in gcc/gcc/tree.c, defines the number of "operands" for an AST node representing an OpenMP reduction clause to be 4:
>
> /* Number of operands for each OpenMP clause. */
> unsigned const char omp_clause_num_ops[] =
> {
> 0, /* OMP_CLAUSE_ERROR */
> 1, /* OMP_CLAUSE_PRIVATE */
> 1, /* OMP_CLAUSE_SHARED */
> 1, /* OMP_CLAUSE_FIRSTPRIVATE */
> 2, /* OMP_CLAUSE_LASTPRIVATE */
> 4, /* OMP_CLAUSE_REDUCTION */
> 1, /* OMP_CLAUSE_COPYIN */
> 1, /* OMP_CLAUSE_COPYPRIVATE */
> 1, /* OMP_CLAUSE_IF */
> 1, /* OMP_CLAUSE_NUM_THREADS */
> 1, /* OMP_CLAUSE_SCHEDULE */
> 0, /* OMP_CLAUSE_NOWAIT */
> 0, /* OMP_CLAUSE_ORDERED */
> 0, /* OMP_CLAUSE_DEFAULT */
> 3, /* OMP_CLAUSE_COLLAPSE */
> 0 /* OMP_CLAUSE_UNTIED */
> };
>
> What does "operand" mean in this context, and why is it 4? A typical reduction clause would look like this:
>
> reduction(+:x)
>
> I would guess either one operand (x) or two for the binary operation +. So this code must imply some different interpretation of the word "operand." Thanks.
If you search for OMP_CLAUSE_REDUCTION in tree.h you will see this
comment:
/* OpenMP clause: reduction (operator:variable_list).
OMP_CLAUSE_REDUCTION_CODE: The tree_code of the operator.
Operand 1: OMP_CLAUSE_REDUCTION_INIT: Stmt-list to initialize the var.
Operand 2: OMP_CLAUSE_REDUCTION_MERGE: Stmt-list to merge private var
into the shared one.
Operand 3: OMP_CLAUSE_REDUCTION_PLACEHOLDER: A dummy VAR_DECL
placeholder used in OMP_CLAUSE_REDUCTION_{INIT,MERGE}. */
Ian
