copy_assumed_shape

Date:

05-29-2011

NAME

copy_assumed_shape - copy assumed-shape dummy array arguments into contiguous local temporary storage

SYNOPSIS

!DIR$ COPY_ASSUMED_SHAPE [ array [, array ]...]

IMPLEMENTATION

Cray Linux Environment (CLE)

DESCRIPTION

The COPY_ASSUMED_SHAPE directive copies assumed-shape dummy array arguments into contiguous local temporary storage upon entry into the procedure in which the directive appears. During execution, it is the temporary storage that is used when the assumed-shape dummy array argument is referenced or defined.

The COPY_ASSUMED_SHAPE directive supports this option:

array

The array is the name of the array to be copied to temporary storage. If no array names are specified, all assumed-shape dummy arrays are copied to temporary contiguous storage upon entry to the procedure. When the procedure is exited, the arrays in temporary storage are copied back to the dummy argument arrays. If one or more arrays are specified, only those arrays specified are copied. The arrays specified must not have the TARGET attribute.

• All arrays, or all assumed-shape dummy arrays if no array argument is provided, specified on a single COPY_ASSUMED_SHAPE directive must be shape-conformant with each other. Incorrect code may be generated if the arrays are not shape-conformant. You can use the -R c command line option to verify that the arrays are shape-conformant.

The COPY_ASSUMED_SHAPE directive applies only to the program unit in which it appears.

Assumed-shape dummy array arguments cannot be assumed to be stored in contiguous storage. In the case of multidimensional arrays, the elements cannot be assumed to be stored with uniform stride between each element of the array. These conditions can arise, for example, when an actual array argument associated with an assumed-shape dummy array is a non-unit strided array slice or section.

If the compiler cannot determine whether an assumed-shape dummy array is stored contiguously or with a uniform stride between each element, some optimizations are inhibited in order to ensure that correct code is generated. If an assumed-shape dummy array is passed to a procedure and becomes associated with an explicit-shape dummy array argument, additional copy-in and copy-out operations may occur at the call site. For multidimensional assumed-shape arrays, some classes of loop optimizations cannot be performed when an assumed-shape dummy array is referenced or defined in a loop or an array assignment statement. The lost optimizations and the additional copy operations performed can significantly reduce the performance of a procedure that uses assumed-shape dummy arrays when compared to an equivalent procedure that uses explicit-shape array dummy arguments.

The COPY_ASSUMED_SHAPE directive causes a single copy to occur upon entry and again on exit. The compiler generates a test at run time to determine whether the array is contiguous. If the array is contiguous, the array is not copied. This directive allows the compiler to perform all the optimizations it would otherwise perform if explicit-shape dummy arrays were used. If there is sufficient work in the procedure using assumed-shape dummy arrays, the performance improvements gained by the compiler outweigh the cost of the copy operations upon entry and exit of the procedure.

SEE ALSO

intro_directives(7)

Cray Fortran Reference Manual