General Form of the FORALL Construct

Rule R215 of the Fortran 90 standard for executable-construct is extended to include the forall-construct.

XBNF forall-construct -to -rule to to is FORALL forall-header forall-body-stmt [ forall-body-stmt ] ... END FORALL

forall-body-stmt -to -rule to to is forall-assignment -to or where-stmt -to or where-construct -to or forall-stmt -to or forall-construct XBNF

• Any procedure referenced in a forall-body-stmt, including one referenced by a defined operation or assignment, must be pure as defined in Section .

• If a forall-stmt or forall-construct is nested in a forall-construct, then the inner FORALL may not redefine any index-name used in the outer forall-construct.

• []Rationale. These statements are allowed in a FORALL construct because they are defined as forms of assignment in Fortran 90 and HPF. The intent is that forall-construct, like forall-stmt, is a block assignment rather than a general-purpose ``parallel loop.'' (End of rationale.)

To determine the set of permitted values for an index-name, we introduce some simplifying notation. In the forall-triplet-spec, let

• be the first subscript (``lower bound'');

• be the second subscript (``upper bound'');

• be the stride; and

• be .

If stride is missing, it is as if it were present with the value 1. The set of permitted values is determined on entry to the construct and is , . The expression stride must not have the value 0. If for some index-name , no forall-body-stmt is executed.

Each assignment nested within a FORALL construct assigns to memory locations specified by the forall-assignment for permitted values of the index-name variables. A program that causes multiple values to be assigned to the same location by a single statement is not HPF-conforming and therefore has no defined meaning. An HPF-conforming program may, however, assign to the same location in syntactically different assignment statements. This is a semantic constraint rather than a syntactic constraint, however; in general, it cannot be checked during compilation.