DECLARE MAPPER

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

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ID 767251

Date 9/08/2022

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DECLARE MAPPER

OpenMP* Fortran Compiler Directive: Declares a user-defined mapper for a specified type. It also lets you optionally declare a map-identifier that can be used in a MAP clause in other directives or in a motion-clause of a TARGET UPDATE directive. This feature is only available for ifx.

Syntax

!$OMP DECLARE MAPPER ([mapper-identifier:] type::var) [clause [[,] clause]...]

mapper-identifier	Is a Fortran identifier, or the literal string DEFAULT. If no `mapper-identifier` is specified, it is as if DEFAULT was specified. A DECLARE MAPPER directive specifying a `mapper-identifier` for a given type is not permitted in a scope where another DECLARE MAPPER directive specifying the same `mapper-identifier` for the same type is accessible.
type	Is an accessible type name within the scope where the directive appears. It cannot be an intrinsic or an abstract type. `type` cannot be directly or indirectly mapped as part of the mapper through another type, except through the appearance of `var` as a list item in a MAP clause. If `type` identifies a derived type, it can be any accessible derived type name. In the Description below, DT refers to a derived type identifier.
var	Is a Fortran identifier. It can be used in all MAP clauses of the DECLARE MAPPER directive. No subobject of `var` is default mapped; all parts of `var` must be explicitly mapped. `var`, or at least one element or component of `var`, must appear in a MAP clause.
clause	Is MAP ([[`map-type-modifier` [ , ] [`map-type-modifier` [ , ] . . .]] `map-type`: ] `list`). `map-type-modifier` is either ALWAYS or CLOSE. `map-type` is ALLOC, TO, FROM or TOFROM. Each `map-type` can appear only once in a MAP clause. If `map-type` is not specified, it is as if TOFROM appeared as the `map-type`. `list` items are limited to references of `var`, or other objects that are accessible in the scope or are previously declared in the scope where the DECLARE MAPPER directive appears. A list item can be an array section.

The DECLARE MAPPER directive is a declarative directive that appears in the specification part of a program. type and mapper-identifier, if present, uniquely identify the mapper.

If a DECLARE MAPPER directive is not specified for a type DT, a predefined mapper exists for type DT as if the type DT had appeared in the directive as follows:

!$OMP DECLARE MAPPER (DT :: var) MAP (TOFROM: var)

A DECLARE MAPPER directive that uses the mapper-identifier DEFAULT for any type DT overrides this predefined mapper for the type DT, and the user-declared mapper becomes the default mapper for all variables of type DT.

If a MAP clause in another directive maps a list item of a type specified in an accessible DECLARE MAPPER directive, or if a motion clause of a TARGET UPDATE invokes a user-defined mapper and updates a list item of type specified by that mapper, the effect is as if the MAP or motion clause is replaced by a set of MAP or motion clauses derived from the MAP clauses specified on the DECLARE MAPPER directive.

A derived type list-item can have more than one map type: one from DECLARE MAPPER, and one from a MAP clause in a TARGET construct.

The following table shows the final map type a mapper applies for a MAP clause that maps a list item of the given type:

The rows are the map-type specified by the mapper.
The columns are the specified map-type of the MAP clause invoking the mapper.
The parenthesized values in the table represent the final map type for a TARGET EXIT DATA construct that invokes a mapper.

In this case, if the mapper specifies map-type ALLOC or TO, and the TARGET EXIT DATA MAP clause that invokes the mapper has map-type FROM, the resulting map-type is RELEASE.

Map result type of map type combinations
	ALLOC	TO	FROM	TOFROM	RELEASE	DELETE
ALLOC	ALLOC	ALLOC	ALLOC (RELEASE)	ALLOC	RELEASE	DELETE
TO	ALLOC	TO	ALLOC (RELEASE)	TO	RELEASE	DELETE
FROM	ALLOC	ALLOC	FROM	FROM	RELEASE	DELETE
TOFROM	ALLOC	TO	FROM	TOFROM	RELEASE	DELETE

If a set of DECLARE MAPPER directives result in a cyclic definition of mappers, it causes unspecified behavior.

Example

The following example contains a DECLARE MAPPER directive that maps derived types of type my_type. The variable var has the type my_type and is used in the MAP clause to reference the derived type and its components.

The MAP clause in the DECLARE MAPPER directive specifies that all components of my_type are mapped, as well as the dynamic storage in the array section var%values(1:NUM_ELEMENTS). No map-type is specified, so the map type TOFROM is assumed.

Variables used in TARGET regions that are of type my_type will be implicitly mapped as prescribed in the DECLARE MAPPER directive’s MAP clause.

  program main 
  integer,parameter      :: nvals = 250
  type my_type
    integer              :: num_vals
    integer, allocatable :: values(:)
  end type 
  type (my_type)          :: t
  !$omp declare mapper (my_type :: var) map (var, var%values (1:var%num_vals))

  t%num_vals = nvals
  allocate (t%values(t%num_vals))
  !$omp target
  call initial_vals (t)
  !$omp end target
  ... 
  contains
    subroutine initial_vals (v)
    type (my_type) :: v
    v%values = 0
    end subroutine initial_vals
   end program

The following example maps the type my_type as seen in the previous example.

Type my_type is nested within another derived type, my_type2. my_type2 is mapped by a second DECLARE MAPPER directive.

The array component unmapped is not mapped and is available on the host only. The component temp is allocated on the target and used as temporary storage on the target device. The component arr is mapped with the default map type TOFROM. The two mappers are combined when mapping variables of type my_type2.

The second DECLARE MAPPER directive uses a mapper-identifier, and maps the variable x and the array y as well as the type my_type2.

program main 
 integer,parameter      :: nvals = 250
 type my_type
   integer              :: num_vals
   integer, allocatable :: values(:)
 end type 
 !$omp declare mapper (my_type :: var) map (var, var%values (1:var%num_vals))

 type my_type2
   type (my_type)        :: my_type_var
   type (my_type)        :: temp
   real,dimension(nvals) :: unmapped
   real,dimension(nvals) :: arr
  end type
  type (my_type2)        :: t
  real                   :: x, y(num_vals)
  !$omp declare mapper (my_mapper : my_type2 :: v) map (v%arr, x, y(:)) &
  !$omp&                map (alloc : v%temp)
    
  !$omp target map (mapper(my_mapper), tofrom : t)
    call calculate(t, x, y)
  !$omp end target
  ... 
   end program

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DECLARE MAPPER

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