DEPEND Clause

Intel® Fortran Compiler Classic and Intel® Fortran Compiler Developer Guide and Reference

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ID 767251

Date 3/22/2024

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DEPEND Clause

Parallel Directive Clause: Enforces additional constraints on the scheduling of a task or loop iterations by enabling dependences between sibling tasks in the task region.

Syntax

It takes one of the following forms:

In Synchronization Directive !$OMP ORDERED

DEPEND (SOURCE) -or-

DEPEND (SINK:vec)

The above forms of the DEPEND clause have been deprecated and replaced by the DOACROSS clause in the ORDERED construct.

In all other directives:

DEPEND ([depend-modifier,] dependence-type : locator-list)

depend-modifier	ITERATOR clause modifier
dependence-type	Can be any one of the following clauses: IN, OUT, or INOUT, MUTEXINOUTSET, INOUTSET, or DEPOBJ. Clauses MUTEXINOUTSET, INOUTSET, and DEPOBJ are only supported for ifx.
locator	If `dependence-type` is DEPOBJ, `locator` must be a depend object in the initialized state. Otherwise, it is a variable or a non-zero length array section. Zero-sized arrays and common block names are not permitted as `locator`-list items. Any `locator`-list item used in a DEPEND clause of the same task or sibling tasks must indicate identical storage or disjoint storage; partial overlap is not permitted. Two locators match if their storage locations are the same, or if the OpenMP reserved locator symbol OMP_ALL_MEMORY appears in the list; in that case, all list items match. If `dependence-type` is OUT or INOUT, `locator` must not be the OpenMP reserved locator OMP_ALL_MEMORY. The behavior is undefined in these cases: If `locator` has the POINTER attribute and its association status is disassociated or undefined If `locator` has the ALLOCATABLE attribute and its allocation status is unallocated Note that this enforced task dependence establishes a synchronization of accesses to each `locator`-list item performed by a dependent task, with respect to accesses to the same `locator`-list item performed by any previous tasks. You must properly synchronize access with respect to other concurrent accesses to each `locator`-list item.
SOURCE	Specifies the satisfaction of cross-iteration dependences that arise from the current iteration.
SINK	Specifies a cross-iteration dependence, where the iteration vector `vec` indicates the iteration that satisfies the dependence.
vec	Is the iteration vector. It has the form: where n is the value specified by the ORDERED clause in the DO loop directive, x_i denotes the loop iteration variable of the i-th nested loop associated with the loop directive, and d_i is a non-negative integer scalar constant. If `vec` does not occur in the iteration space, the DEPEND clause is ignored. Note that if `vec` does not indicate a lexicographically earlier iteration, it can cause a deadlock. For a `vec` element form of x_i + d_i or x_i - d_i, the expression x_i + d_i or x_i - d_i for any value of the integer loop iteration variable x_i that can encounter the ordered construct must be computable in the loop iteration variable's type without overflow.

Rules related to sibling task dependency:

The generated task is a dependent task of the sibling task if any of the following are true:
- If one or more locator-list items specified in dependence-type IN matches a locator-list item appearing in any of the following DEPEND clause dependence-types on a construct that previously generated a sibling task: OUT, INOUT, MUTEXINOUTSET, or INOUTSET.
- If one or more locator-list items specified in dependence-type OUT or INOUT matches a locator-list item appearing in any of the following DEPEND clause dependence-types on a construct that previously generated a sibling task: IN, OUT, INOUT, MUTEXINOUTSET, or INOUTSET.
- If one or more locator-list items specified in dependence-type INOUTSET matches a locator-list item appearing in any of the following DEPEND clause dependence-types on a construct that previously generated a sibling task: IN, OUT, INOUT, or MUTEXINOUTSET.
- If one or more locator-list items specified in dependence-type MUTEXINOUTSET matches a locator-list item appearing in any of the following DEPEND clause dependence-types on a construct that previously generated a sibling task: IN, OUT, INOUT, or INOUTSET.
The sibling tasks are mutually exclusive if the following is true:
- If one or more locator-list items specified in dependence-type MUTEXINOUTSET matches a locator-list item appearing in a DEPEND clause with MUTEXINOUTSET dependence-type on a different task generating construct and both constructs generate sibling tasks.

When dependence-type is DEPOBJ, the locators must all be depend objects. The dependence-types are derived from the depend objects. For each depend object, the behavior is as if the current construct contained the DEPEND clause of the most recently executed DEPOBJ construct that initialized or updated the depend object.

If a DEPEND clause appears in a TARGET or TARGET UPDATE directive, it is treated as if it had appeared on the implicit task construct that encloses the TARGET construct.

Parent topic: C to D

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Intel® Fortran Compiler Classic and Intel® Fortran Compiler Developer Guide and Reference

DEPEND Clause

Syntax

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