CPU FLAGS X86

The USE flags corresponding to the instruction sets and other features specific to the x86 (amd64) architecture are being moved into a separate USE flag group called CPU_FLAGS_X86.

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

USE="mmx mmxext sse sse2 sse3"

Those flags need to be copied into:

CPU_FLAGS_X86="mmx mmxext sse sse2 sse3"

Please note that the same CPU_FLAGS_X86 variable is used both on x86 and amd64 systems.

When in doubt, you can consult the flag descriptions using one of the commonly available tools, e.g. `equery uses` from gentoolkit:

$ equery uses media-video/ffmpeg

Most of the flag names match /proc/cpuinfo names, with the notable exception of SSE3 which is called 'pni' in /proc/cpuinfo (please also do not confuse it with distinct SSSE3).

To help users enable the correct USE flags, we are providing a Python script that generates the correct value using /proc/cpuinfo. It can be found in the app-portage/cpuinfo2cpuflags package:

$ emerge -1v app-portage/cpuinfo2cpuflags $ cpuinfo2cpuflags-x86

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.