mem-cache: Factor ReplaceableEntry out

ReplaceableEntry is referenced by many classes that do
not necessarily need access to the replacement policies.
Therefore, in order to allow better compilation units,
we factor it out to a new file.

Change-Id: I0823567bf1ca336ffcdf783682ef473e8878d7fd
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/13418
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>

mem-cache: Use set and way for ReplaceableEntry

Replaceable entries belong to table-like structures, and therefore
they should be indexable by combining a row and a column. These,
using conventional cache nomenclature translate to sets and ways.

Make these entries aware of their sets and ways. The idea is to
make indexing policies usable by other table-like structures. In
order to do so we move sets and ways to ReplaceableEntry, which
will be the common base among table entries.

Change-Id: If0e3dacf9ea2f523af9cface067469ccecf82648
Reviewed-on: https://gem5-review.googlesource.com/c/12764
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>

mem-cache: ReplacementPolicy specific replacement data

Replacement data is specific for each replacement policy, and thus
should be instantiated differently by each policy.

Touch() and reset() do not need to be aware of CacheBlk, as they
only update its ReplacementData.

Invalidate() makes replacement policies independent of cache blocks,
by removing the awareness of the valid state.

An inheritable base ReplaceableEntry class was created to allow usage
of replacement policies with any table-like structure.

Change-Id: I998917d800fa48504ed95abffa2f1b7bfd68522b
Reviewed-on: https://gem5-review.googlesource.com/9421
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>

mem-cache: Split array indexing and replacement policies.

Replacement policies (LRU, Random) are currently considered as array
indexing methods, but have completely different functionalities:

- Array indexers determine the possible locations for block allocation.
This information is used to generate replacement candidates when
conflicts happen.
- Replacement policies determine which of the replacement candidates
should be evicted to make room for new allocations.

For this reason, they were split into different classes. Advantages:

- Easier and more straightforward to implement other replacement
policies (RRIP, LFU, ARC, ...)
- Allow easier future implementation of cache organization schemes

As now we can't assure the use of sets, the previous way to create a
true LRU is not viable. Now a timestamp_bits parameter controls how
many bits are dedicated for the timestamp, and a true LRU can be
achieved through an infinite number of bits (although a few bits suffice
in practice).

Change-Id: I23750db121f1474d17831137e6ff618beb2b3eda
Reviewed-on: https://gem5-review.googlesource.com/8501
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>