[release/9.0] Fix optimization of Vector512 AndMask + NotMask to AndNotMask #108803
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Backport of #108775 to release/9.0
/cc @BruceForstall
Customer Impact
Found by fuzz testing. The bug causes either bad code generation or JIT crash in a specific case of optimizing Vector512 "and" and "not" on masks to the combined "AndNotMask" on AVX-512 machines.
For example:
(user code:) Vector512.AndNot(Vector512.Equals(v1, v2), Vector512.Equals(v3, v4))
=> (internally) AndMask(m1, NotMask(m2))
=> (internally) AndNotMask(m2, m1)
This internal transformation fails with this bug.
Regression
I believe this is not a regression, but represents a test hole.
Testing
Reduced fuzzing test used to verify. Created a small test based on this to verify, and add to the regression tests as part of this change.
Risk
Low. Very simple, isolated fix.