On Tue, 11 Feb 2020, Segher Boessenkool wrote: > Hi! > > On Tue, Feb 11, 2020 at 03:46:05PM +0300, Roman Zhuykov wrote: > > Hmm, even when trying to move it just few passes earlier many years ago, > > got another opinion: > > https://gcc.gnu.org/ml/gcc-patches/2011-10/msg01526.html > > Although without such a move we still have annoying issues which RTL > > folks can't solve, see e.q. > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93264#c2 > > Basic block partitioning has wildly disproportionate fallout in all > later passes, both in terms of what those *do* (or don't, if partitioning > is enabled), and of impact on the code (not to mention developer time). > > Maybe the implementation can be improved, but probably we should do this > in a different way altogether. The current situation is not good.
I think the expectation that you can go back to CFG layout mode and then work with CFG layout tools after we've lowered to CFG RTL is simply bogus. Yeah, you can probably do analysis things but I wouldn't be surprised if a CFG RTL -> CFG layout -> CFG RTL cycle can wreck things. Undoubtedly doing CFG manipulations is not going to work since CFG layout does not respect CFG RTL restrictions. Partitioning simply uncovered latent bugs, there's nothing wrong with it IMHO. Richard.
