https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114480
--- Comment #11 from Vladimir Makarov <vmakarov at gcc dot gnu.org> --- My finding is that RA is not a problem for GCC speed with -O1 and up. RA in -O0 does really consume a big portion of GCC compiler time. The biggest part of RA in -O0 is actually spent in life analysis. It is difficult to implement a modest RA w/o life analysis as it will results in huge stack slot generation (not knowing pseudo lives basically means allocating stack slot for each pseudo). The problem with the test is a huge number of pseudos (or IRA objects). This results in a big sparse set (which can be hardly placed in L3 cache) and bad cache behaviour. I tried to use a bitmap instead of sparse set, but GCC crashed after allocating 48GB memory. Sbitmap works better and improves IRA time by 12%. But it works worse for other more frequently use cases. So I don't think that RA behaviour can be improved for this case.
