# qopt-zmm-usage, Qopt-zmm-usage

Defines a level of zmm registers usage.

## Syntax

Linux: | -qopt-zmm-usage=keyword

macOS: | -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 pragma omp simd simdlen(n) or on functions that are generated by vector specifications specific to CORE-AVX512.

## IDE Equivalent

None

## Alternate Options

None

Parent topic: Advanced Optimization Options

## See Also

x, Qx compiler option

For more information about simd loops specification and vector function specification, see pragmas omp simd and omp declare simd in the OpenMP* TR4: Version 5.0 specification.