According to [1] ebuilds should not have use flags for build system options that do not pull in conditional assembly code. The --enable-sse option to configure only adds "-msse -mfpmath=sse" to CFLAGS. Take a look at configure.ac (search for sse) to verify this. Thus $(use_enable cpu_flags_x86_sse sse) should be replaced with --disable-sse. [1] https://wiki.gentoo.org/wiki/CPU_FLAGS_X86_conversion (point 6) Reproducible: Always
well, -mfpmath=sse must not be used at global scope since it breaks standards; however, some packages do not rely on standard-compliant floating point computations and can add this; but this obviously adds sse instructions so they should add this only with sse (or its use-expanded equivalent) useflag enabled this is clearly something that should be fixed in the documentation
