On 8/25/22 01:01, Richard Henderson wrote:
One notable
difference is that the new decoder always sign-extends 8-bit immediates,
so for example a "cmpb $e9, %dl" instruction will subtract $0xfff...fffe9
from the temporary value. This is the way Intel intended "Ib" immediates
to work, and there's no difference between the two.
That is in fact an improvement.
Yes, it is and it is a direct effect of encoding the operand types and
sizes in a table, instead of writing ad hoc code everywhere.
Anyay, porting these opcodes is really more of a validation for the
whole concept and a test for the common decoder code; it's probably more
efficient to focus on the SSE and VEX 2-byte and 3-byte opcodes as a path
towards enabling AVX in QEMU, and keep the existing decoder for non-VEX,
non-SSE opcodes.
Eh... I disagree. I would really hate to retain the existing decoder.
This is already so much better...
Absolutely, it's just a matter of programmer efficiency, and then
SSE/AVX is where I would start.
I would hate to not get there just because I didn't have time to
complete the last sixty-ish one-byte opcodes (which are also the ones
that benefit the least from table-driven decoding; that's already
visible in 90-9F).
This was just a heads up that if I complete this patchset I would
probably ask to have it committed with "just" SSE/AVX (plus the BMI VEX
instructions), in a similar spirit to how the Meson conversion only
covered Makefiles.
Paolo
