Not supposed to touch flags at all, so don't! instead of making a terrible mess
of csels. a lot less instructions, and probably faster because the branch should
be predicted correctly in practice in hot loops.
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Instruction count CI has transformed the way we work on FEX… I love the system
and want to make it better. there’s one part of instruction count CI that isn’t
so lovable: the problematic “optimal” flag on instructions.
There are several issues with this flag, both philosophical and practical.
– it is tedious to update the optimal flag when making an implementation
optimal. The effect of that is discouraging people from making instructions,
optimal, or encouraging people to fail to update the flag, and dilute the value
of it. Either way, since we care far more about optimal implementations, then we
do about updating the flag, clearly we should prioritize the implementation and
not the flag. This issue was not obvious at the outset, when instruction count,
CI was introduced, and still quite small. The problem magnified when we started
duplicating instructions in bulk for different combinations of CPU features
(flagm, AFP, etc.) that intern multiplies the manual work required to update the
flags by the corresponding constant factor. if it comes down to a choice between
removing this extra coverage and removing the flag, I think we all agree that
removing the flag is the lesser evil.
– The definition of “optimal” is fundamentally problematic. I have often
improved the instruction count of an instruction that was already “optimal”.
This is all kinds of silly, and calls into question whether there’s any value
whatsoever in the existing classifications of the flag. Furthermore, it is often
unknowable, whether an implementation really is optimal. Is it possible to
implement BZHI (with flag calculations) in fewer than eight instructions? We
don’t know, and it’s silly to pretend that we do.
– as a consequence of the problematic definitions , there are so many errors in
both directions that I don’t think there’s much value in preserving the existing
classification at the expense of +progress. Being able to say “32% of
instructions are translated optimally” is neat, but it really doesn’t tell us
anything whatsoever when you dig a little deeper.
So, as the flag is misleading at best and perhaps harmful at worst, let’s remove
it and make the instruction count CI, more useful overall. let’s let the
expected count and the assembly speak for themselves, and cut away the chaff. if
we want a meaningless number to report to management, we can instead calculate
the average blowup factor ;-)
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
If a bind fails then this is usually because PID reuse happened and the
unix domain socket path still existed on the filesystem. Alternatively
the process did an execve which left a dangling unix domain file.
Unlink the file and try again in these cases. It will almost certainly
work the second time.
Instead of relying on sleeping in accept, use poll. This allows us to
early shutdown instead of leaving a thread hanging stuck in accept.
Doesn't change behaviour with FEX gdbserver waiting for attach, but in
the future when we all full process trees to have gdbserver running this
will be more important.
Using the server mount folder works most of the time, but when running
under pressure-vessel this stacks directories in a weird way because the
mount folder has some tricks applied to it.
Expose the temp folder being used directly instead.
These are setup to be nullptr by default. Instead of providing no-op
lock instructions just have them be nullptr.
It's already part of the API that they need to be nullptr checked before
calling and this matches behaviour of the real libX11 library. Removes
some spam that is unnecessary.
Unused since TestNZ+NZCVSelect accomplishes the same and good riddance. Might
bring them back later for tbz/tbnz, but certainly not in this Selectful form.
(I added them when I thought we were going to RA the flags. With the more
effective static approach, we don't need this for that.)
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Now unused. If we bring it back, it should be brought back as CSSC only. On
non-CSSC platforms, an explicit cmp + predicated neg can be better.
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Separate out the NZCV bits from the more complex stuff so we can specially
optimize the branches.
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
In this mode, rather than the branch comparing its arguments and then jumping
based on the result, the branch simply jumps by the native comparison based on
the NZCV value. This allows us to map x86 branches to arm64 branches 1:1.
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Resolving the issue that we can only ever have one gdbserver process
running consuming port 8086 (even if the port number is cute).
Doesn't give us anything yet but in the future will allow us to have
whole process trees running gdbservers that we can attach to.
Usually better in practice... some rotates are slightly regressed by this but
they were already terrible.
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Ryan Houdek