Absence of Loop-carried Memory Dependency with IVDEP Directive

For Itanium®-based applications, the -ivdep_parallel option indicates there is absolutely no loop-carried memory dependency in the loop where IVDEP directive is specified. This technique is useful for some sparse matrix applications. For example, the following loop requires -ivdep_parallel in addition to the directive IVDEP to indicate there is no loop-carried dependencies.

Example

#pragma ivdep

for(i=1; i<n; i++)

{

e[ix[2][i]]=e[ix[2][i]]+1.0;

e[ix[3][i]]=e[ix[3][i]]+2.0;

}

The following example shows that using this option and the IVDEP directive ensures there is no loop-carried dependency for the store into a().

Example

#pragma ivdep

for(j=0; j<n; j++)

{

a[b[j]]=a[b[j]]+1;

}