3 ms·
I seem to remember the original Intel MMX aliased its integer SIMD registers with the x87 FPU registers (for compatibility with non-MMX OSes when saving/restori
by flopsamjetsam 4y ago
I seem to remember the original Intel MMX aliased its integer SIMD registers with the x87 FPU registers (for compatibility with non-MMX OSes when saving/restoring state when switching between processes). I never wrote code for it, but I remember it was slow to switch between the two modes.
- astrange 4y agoIt does, which meant the ISA has the strange requirement that you have to emit an 'emms' instruction once you're done using MMX or else x87 operations won't work. This makes MMX very unpopular outside controlled situations, so compiler autovectorization doesn't support it.