cpu-minor: Disentangle the PC and fetch address.

The minor CPU was using a PCState object both to track redirects when
taking a branch, etc, and to track where to fetch a line of memory from.
It would need to create a new PCState object, or at least update the
existing one, whenever it needed to advance to the next line.

This is problematic since it means the minor CPU needs to know how to
create or set a PCState object, and since it by necessity only
understands the most basic aspect of a PCState, what the address is, it
can only set that, with all the other potential attributes staying at
their old values or getting set to some default.

Instead, this change separates the two. There is now a PC which is used
for redirects which the later stages will only pick up if there is a
change in "sequence", the same behavior as before. This PC will only
ever be set when changing sequence, and will otherwise not be

There is also now a separate fetch address which is what the fetch stage
uses to get new lines. This was all the PC value that was artificially
updated was used for anyway.

Change-Id: Ia64bbe21e980566ae77786999689c9c8a94e9378
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/52048
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: ZHENGRONG WANG <seanyukigeek@gmail.com>
Maintainer: ZHENGRONG WANG <seanyukigeek@gmail.com>
3 files changed