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Cray Standard C/C++ Reference Manual

surprising results. In some cases the compiler’s scoping choices do not meet

requirements or expectations.

The defaults clause of the Autotasking parallel or taskloop directive

instructs the compiler to use a simple set of heuristic scoping rules. This

contrasts with cncall, in which the compiler exploits all available dependence

information in its analysis. Given the inherent ambiguities introduced by

calls, neither approach can be guaranteed to produce correct results in all

circumstances.

When the translation of a cncall loop (a loop preceded by a cncall

directive) is in doubt, you should check the tasking information messages. The

-hreport=t option on the CC(1) and cc(1) command lines reports scoping

choices for cncall loops through messages 6421, 6422, and 6423. For more

information on the -hreport=t option, see Section 2.18.3, page 31.

3.8.3 parallel and endparallel Directives (UNICOS Systems)

Scope: Local

The parallel directive marks the start of a parallel region. The endparallel

directive marks the end of a parallel region. Parallel regions are combinations of

redundant code blocks (executed by all processors) and partitioned code blocks

(portions executed by each processor, such as the iterations of a tasked loop). The

parallel directive indicates where multiple processors enter execution, which

may be different from where they demonstrate a direct benefit (partitioned code

block). The format of these directives is as follows:

#pragma _CRI parallel [shared(var...)][private(var...)]

[value(var...)][defaults][if (exp)][maxcpus (exp)]

#pragma _CRI endparallel

Arguments to tasking directives are described in Section 3.8.13, page 79.

3.8.4 taskloop Directive (UNICOS Systems)

Scope: Local

The taskloop directive indicates that the following for loop can be executed

in parallel by multiple processors. Although no directive is needed to end a

taskloop loop, the endloop directive (see Section 3.8.5, page 71) can be used to

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Vax C90-EL SERIES Service Manual Page 90