CPU FLAGS X86

CPU_FLAGS_X86 is an USE_EXPAND variable containing instruction set and other CPU-specific features.

Previously USE flags corresponding to the instruction sets and other features specific to the / architecture are being moved into a separate USE_EXPAND variable called CPU_FLAGS_X86.

Optimization
In order not to lose CPU-specific optimizations, users will be required to update the (and potentially ) file. For example, if the following USE flags were present:

Those flags need to be copied to a newly created CPU_FLAGS_X86 variable:

When in doubt, consult the flag descriptions using one of the commonly available tools, e.g. from :

Most of the flag names match names, with the notable exception of   which is called   in  (please also do not confuse it with distinct  ).

To help users enable the correct USE flags, a Python script is provided that generates the correct value using. It can be found in the package.

Saving deprecated USE flags
In order to ensure safe migration and maintain compatibility with external repositories, it is recommended to preserve the old USE settings for a period of one year or until no package of interest is still using them.

Invocation
Version 1 or 2:

Version 3 or greater:

Example to apply globally:

External resources

 * https://gitweb.gentoo.org/data/gentoo-news.git/plain/2015-01-28-cpu_flags_x86-introduction/2015-01-28-cpu_flags_x86-introduction.en.txt - CPU_FLAGS_X86 enews introduction.
 * https://packages.gentoo.org/useflags/search?q=cpu_flags_x86 - A online package search for all packages that make use of CPU_FLAGS_X86 values.