[Bug rtl-optimization/113495] RISC-V: Time and memory awful consumption of SPEC2017 wrf benchmark

["rdapp at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113495

--- Comment #27 from Robin Dapp <rdapp at gcc dot gnu.org> ---
Following up on this:

I'm seeing the same thing Patrick does.  We create a lot of large non-sparse
sbitmaps that amount to around 33G in total.

I did local experiments replacing all sbitmaps that are not needed for LCM by
regular bitmaps.  Apart from output differences vs the original version the
testsuite is unchanged.

As expected, wrf now takes longer to compiler, 8 mins vs 4ish mins before and
we still use 2.7G of RAM for this single file (Likely because of the remaining
sbitmaps) compared to a max of 1.2ish G that the rest of the commpilation uses.

One possibility to get the best of both worlds would be to threshold based on
num_bbs * num_exprs.  Once we exceed it switch to the bitmap pass, otherwise
keep sbitmaps for performance. 

Messaging with Juzhe offline, his best guess for the LICM time is that he
enabled checking for dataflow which slows down this particular compilation by a
lot.  Therefore it doesn't look like a generic problem.