the relevant target hw (e.g. apple m1) supports this, so let's track with it on.
Secondary_REP and VEX_map1 are duplicated to have frintts and !frintts versions
so we can track the non-frintts path instead, since armv8.5 is still kinda new.
the rest just enable on to minimize combinatorics.
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
to see the impact of Billy's stuff in a real world context since we don't have
hot blocks for it yet. random blocks I pulled from Control_DX11.exe which I had
handy, with rip relative addressing replaced.
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>
Some simple tests to showcase instructions that we can optimize.
- Back to back pushes could be optimized
- Back to back scalar vector operations can be optimized
- Show with AFP that back to back scalar is already optimal
- Also ensures we don't break this stage.
Alyssa Rosenzweig