We currently have a bug when calling Arm64GPRCache::Flush with
FlushMode::MaintainState, zero free host registers, and at least
one guest register containing an immediate. We end up grabbing
a temporary register from the register cache in order to be
able to write the immediate to memory, but grabbing a temporary
register when there are zero free registers causes the least
recently used register to be flushed in a way which does not
maintain the state of the register cache.
To get around this, require callers to pass in a temporary
register in the GPR MaintainState case. In other cases,
passing in a temporary register is not required but can help
avoid spilling a register (if the caller already had a
temporary register at hand anyway, which in particular will
be the case in my upcoming memcheck pull request).
302b47f5e6