OpenMP-Examples/program_control/assumption.tex

%\pagebreak
\section{Assumption Directives}
\label{sec:assumption}
%\index{assumption!assume directive@\kcode{assume} directive}
%\index{assumption!assumes directive@\kcode{assumes} directive}
\index{directives!assume@\kcode{assume}}
\index{directives!assumes@\kcode{assumes}}
\index{assume directive@\kcode{assume} directive}
\index{assumes directive@\kcode{assumes} directive}

\index{directives!begin assumes@\kcode{begin assumes}}
\index{begin assumes directive@\kcode{begin assumes} directive}

\index{no_parallelism clause@\kcode{no_parallelism} clause}
\index{clauses!no_parallelism@\kcode{no_parallelism}}
\index{holds clause@\kcode{holds} clause}
\index{clauses!holds@\kcode{holds}}

Assumption directives provide additional information about the expected properties of 
the program that may be used by an implementation for optimization. 
Ignoring this information should not alter the behavior of the program. The C/C++ example 
shows the use of delimited scope (Case 1) and block-associated (Case 2) assumption directives.
A similar effect is shown for Fortran where the \kcode{assumes} directive is used in the module (Case 1)
and the block-associated directive uses an \kcode{end assume} termination (Case 2). 
The function \ucode{fun} is annotated with the \kcode{no_parallelism} clause, using the \kcode{begin assumes} 
(C) or \kcode{assumes} (Fortran) directive, to indicate that no implicit/explicit tasks are generated and no 
SIMD constructs are encountered during execution of the function. If the function \ucode{fun} contains 
task-generating or SIMD constructs then the behavior would be undefined. The block-associated 
\kcode{assume} directive is used to indicate that \ucode{N} is a multiple of 8 and 
will always be equal to or greater than 1. This information, if used for optimization,
could eliminate additional checks.

\cexample[5.1]{assumption}{1}
\ffreeexample[5.1]{assumption}{1}