Vax C90-EL SERIES Service Manual download pdf (Page 39)

Compiler Commands [2]

2.10.2 -h [no]ivdep (CC, cc)

Default option: -h noivdep

The -h ivdep option instructs the compiler to ignore vector dependencies

for all loops. This is useful for vectorizing loops that contain pointers. With

-h noivdep, loop dependencies inhibit vectorization. To control loops

individually, use the #pragma ivdep directive, as discussed in Section 3.7.1,

page 58.

This option can also be used with "vectorization-like" optimizations on

UNICOS/mk systems. See Section 3.7, page 57, for more information.

Caution: This option should be used with extreme caution because incorrect

results can occur if there is a vector dependency within a loop. Combining

this option with inlining is dangerous because inlining can introduce vector

dependencies.

2.10.3 -h vectorn (CC, cc)

Default option: -h vector2

The -h vectorn option specifies the level of automatic vectorizing to be

performed. Vectorization results in dramatic performance improvements with

a small increase in object code size. Vectorization directives are unaffected by

this option.

On UNICOS/mk systems, the Cray Standard C/C++ compilers can perform

optimizations that are similar to vectorization on loops that contain calls to

certain functions. These optimizations are enabled or disabled with this option.

See Section 3.7, page 57, for more information on these optimizations.

Argument n can be one of the following:

Description

0 No automatic vectorization.

1 Conservative automatic vectorization. On UNICOS systems,

automatic vectorization is performed. Search loops and reduction

loops are not vectorized.

2 Moderate automatic vectorization. On UNICOS systems,

automatic vectorization is performed as with vector1, and

vectorization of search loops and reduction loops is added.

3 Aggressive automatic vectorization. Automatic vectorization is

performed as with vector2 and restructuring of loops is done to

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Vax C90-EL SERIES Service Manual Page 39