In the latest version of dcache, replace pipe is blocked by main pipe according to set, because replace and store/probe should not try to modify data or meta at the same time, which might result in inconsistency between data and meta. For performance reasons, replace is blocked by store, not the other way around, because replace can be delayed so it can bring dirty data written by store down to L2.

Now this consideration brings another dead-lock. Store buffer keeps sending store request without a break, so main pipe stays occupied handling store. In the meantime, miss queue rejects these store request so store buffer keeps replaying all the time. Replace pipe cannot advance because of set conflict with main pipe, so the corresponding miss entry cannot be released and keeps rejecting new store request.

To break this dead-lock, this pull request tries to set replace pipe higher priority than main pipe, and let write-back queue handle consistency between data and meta if a store interrupts.