mirror of
https://git.ffmpeg.org/ffmpeg.git
synced 2026-10-28 15:19:38 +03:00
44e1b60c6a
Rather than having two uops for the C reference code and a separate
uop for the x86 backend, we can just implement the C reference
using the same register-register assignment logic.
This results in only slightly worse codegen, since the compiler is
smart enough to eliminate the unnecessary copies.
The main downside is the fact that we need to allocate extra stack space
to back-fill the remaining (unused) pointers. In theory, we could do this
more efficiently by re-using unused *input* registers directly, but that
would require a lot of reliance on compile-time constant folding teasing
apart the entire register index tracking loop and duplicate check, so this
is a useful middle ground.
On platforms like x86, we still don't care about the PERMUTE vs
COPY distinction, but it's also harmless (2-3 extra lines to
instantiate the underlying MOVE macro on both uop variants).
Finally, we need to add a mask to the move uops to keep track of which
outputs are actually needed (especially for checkasm). Though it does result
in the rather unfortunate downside that it bloats the names of the uop
names.
The op lists change to reflect the new representation, e.g.:
rgb24 16x16 -> bgr24 16x16:
[ u8 +++X] SWS_OP_READ : 3 elem(s) packed >> 0
min: {0 0 0 _}, max: {255 255 255 _}
[ u8 +++X] SWS_OP_SWIZZLE : 2103
min: {0 0 0 _}, max: {255 255 255 _}
[ u8 XXXX] SWS_OP_WRITE : 3 elem(s) packed >> 0
('X' unused, 'z' byteswapped, '=' copied, '$' const, '+' integer, '0' zero)
translated micro-ops:
u8_read_packed_xyz
- u8_permute_zyxw
+ u8_permute_xyzw_txz_xzt
u8_write_packed_xyz
Signed-off-by: Niklas Haas <git@haasn.dev>