Intel® Fortran Compiler Classic and Intel® Fortran Compiler Developer Guide and Reference

ID 767251
Date 3/22/2024
Public

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Document Table of Contents

qopt-zmm-usage, Qopt-zmm-usage

Defines a level of zmm registers usage.

Syntax

Linux:

-qopt-zmm-usage=keyword

Windows:

/Qopt-zmm-usage:keyword

Arguments

keyword

Specifies the level of zmm registers usage. Possible values are:

low

Tells the compiler that the compiled program is unlikely to benefit from zmm registers usage. It specifies that the compiler should avoid using zmm registers unless it can prove the gain from their usage.

high

Tells the compiler to generate zmm code without restrictions.

Default

varies

The default is low when you specify [Q]xCORE-AVX512.

The default is high when you specify [Q]xCOMMON-AVX512.

Description

This option may provide better code optimization for Intel® processors that are on the Intel® microarchitecture formerly code-named Skylake.

This option defines a level of zmm registers usage. The low setting causes the compiler to generate code with zmm registers very carefully, only when the gain from their usage is proven. The high setting causes the compiler to use much less restrictive heuristics for zmm code generation.

It is not always easy to predict whether the high or the low setting will yield better performance. Programs that enjoy high performance gains from the use of xmm or ymm registers may expect performance improvement by moving to use zmm registers. However, some programs that use zmm registers may not gain as much or may even lose performance. We recommend that you try both option values to measure the performance of your programs.

This option is ignored if you do not specify an option that enables Intel® AVX-512, such as [Q]xCORE-AVX512 or option [Q]xCOMMON-AVX512.

This option has no effect on loops that use directive SIMD SIMDLEN(n) or on functions that are generated by vector specifications specific to CORE-AVX512.

IDE Equivalent

None

Alternate Options

None

See Also