via the 0 reg. We really need a more generalized approach to taking advantage of
wzr, but this optimizes the special case I care about for seta (saving a move to
make the impl optimal).
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
This will replace Select soon, as it lets us take advantage of
NZCV-generating instructions and it doesn't clobber NZCV.
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Do it explicitly for sve-256 and punt on optimizing, so we avoid regressing code
gen otherwise.
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Rather than the context. Effectively a static register allocation scheme for
flags. This will let us optimize out a LOT of flag handling code, keeping things
in NZCV rather than needing to copy between NZCV and memory all the time.
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Some opcodes only clobber NZCV under certain circumstances, we don't yet have
a good way of encoding that. In the mean time this hot fixes some would-be
instcountci regressions.
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Again we need to handle this one specially because the dispatcher can't insert
restore code after the branch. It should be optimized in the near future, don't
worry.
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Semantics differ markedly from the non-NZCV flags, splitting this out makes it a
lot easier to do things correctly imho. Gets the dest/src size correct
(important for spilling), as well as makes our existing opt passes skip this
which is needed for correctness at the moment anyway.
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
This fixes an issue where CPU tunables were ending up in the thunk
generator which means if your CPU doesn't support all the features on
the *Builder* then it would crash with SIGILL. This was happening with
Canonical's runners because they typically only support ARMv8.2 but we
are compiling packages to run on ARMv8.4 devices.
cc: FEX-2311.1
SHA instructions are very large right now and cause register spilling
due to their codegen. Ender Lilies has a really large block in a
function called `sha1_block_data_order` that was causing FEX to spill
NZCV flags incorrectly. The assumption which held true before NZCV
optimizations were a thing was that all flags were either 1-bit in an
8-bit container, or just 8-bit (x87 TOP flag).
NZCV host flags broke this assumption by making its flags 32-bit which
ended up breaking when encounting spilling situations.
Replace every instance of the Op overwrite pattern, and ban that anti-pattern
from the codebase in the future. This will prevent piles of NZCV related
regressions.
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
The "create op with wrong opcode, then change the opcode" pattern is REALLY
dangerous. This does not address that. But when we start doing NZCV trickery, it
will get /more/ dangerous, and so it's time to add a helper and make the
convenient thing the safe(r) thing. This helper correctly saves NZCV /before/
the instruction like the real builders would. It also provides a spot for future
safety asserts if someone is motivated.
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
It looks like currently FEX has a bug around implicit flag clobbering
with this pull request where an IR operation that implicitly clobbers
flags isn't correctly saving the NZCV flags before doing the operation.
Adds a unit test that specifically captures this issue. RAX will be 1 or
0 depending on if the flags are clobbered incorrectly or not.
Alyssa Rosenzweig