In the case where the prioritised round-robin source does not have a
request, this was always picking the earliest source that had one, which
means if some sources are making more requests than others (e.g. there
is lots of D$ churn but the I$ has a high hit rate) then, whilst the
cycles where srcRR[dst] prioritises a source that is making requests are
fair, the cycles where it prioritises a source that is not making
requests is not fair, since then the earlier sources will be
prioritised. Instead, make the fallback priority similarly dynamic so we
cycle through the order we look at the sources in.
This currently just loads in the data on cache miss, so won't help to reduce DRAM overhead, but will be forwards compatible and save on instructions in the revoker loop.
Also, assume that a target that is not taken should be removed from the
Btb. (The read that checked isn't possible with BRAM timing unless we
latched and had an extra port, but removing the check actually improved
performance a bit in CoreMark, and the pipeline should actually only be
reporting a non-taken branch if we did something wrong.)
This includes renaming Fifo.bsv to Fifos.bsv to account for a case insensitive file system which confuses this library with FIFO.bsv.
Also this includes an update of the verilator flags that are needed for modern verilator.
Finally, some verilator flag changes for building with LLVM.
