They're now stored in ConstantPropagation instead.
I've also removed the LocationType enum. The location of each guest
register is now tracked using three booleans: Whether it is in ppcState,
whether it is in a host register, and whether it is a known immediate.
The first two of these booleans are stored in the register cache, and
the last one is stored in ConstantPropagation. This new model allows us
to handle the combination of a value simultaneously being in a host
register and being a known immediate. It also keeps track of which
registers are dirty, which was previously kept track of in X64CachedReg.
The old model maps to the new model as follows:
default host_reg immediate
Default true false false
Discarded false false false
Bound (!dirty) true false
Immediate false false true
SpeculativeImmediate true false true
[previously unrepresentable] (!dirty) true true
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