https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108500
--- Comment #20 from Vladimir Makarov <vmakarov at gcc dot gnu.org> --- (In reply to Richard Biener from comment #14) > Thanks for the new testcase. With -O0 (and a --enable-checking=release > built compiler) this builds in ~11 minutes (on a Ryzen 9 7900X) with > > integrated RA : 38.96 ( 6%) 1.94 ( 20%) 42.00 ( > 6%) 3392M ( 23%) > LRA non-specific : 18.93 ( 3%) 1.24 ( 13%) 23.78 ( > 4%) 450M ( 3%) > LRA virtuals elimination : 5.67 ( 1%) 0.05 ( 1%) 5.75 ( > 1%) 457M ( 3%) > LRA reload inheritance : 318.25 ( 49%) 0.24 ( 2%) 318.51 ( > 48%) 0 ( 0%) > LRA create live ranges : 199.24 ( 31%) 0.12 ( 1%) 199.38 ( > 30%) 228M ( 2%) > 645.67user 10.29system 11:04.42elapsed 98%CPU (0avgtext+0avgdata > 30577844maxresident)k > 3936200inputs+1091808outputs (122053major+10664929minor)pagefaults 0swaps > I've tried test-1M.i with -O0 for clang-14. It took about 12hours on E5-2697 v3 vs about 30min for GCC. The most time (99%) of clang is spent in "fast register allocator": Total Execution Time: 42103.9395 seconds (42243.9819 wall clock) ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Name --- 41533.7657 ( 99.5%) 269.5347 ( 78.6%) 41803.3005 ( 99.3%) 41942.4177 ( 99.3%) Fast Register Allocator 139.1669 ( 0.3%) 16.4785 ( 4.8%) 155.6454 ( 0.4%) 156.3196 ( 0.4%) X86 DAG->DAG Instruction Selection I've tried the same for -O1. Again gcc took about 30min and I stopped clang (with another used RA algorithm) after 120hours. So the situation with RA is not so bad for GCC. But in any case I'll try to improve the speed for this case. > so register allocation taking all of the time. There's maybe the possibility > to gate some of its features on the # of BBs or insns (or whatever the actual > "bad" thing is - I didn't look closer yet). > > It also seems to use 30GB of peak memory at -O0 ... > I see only 3GB. Improving this is hard task. The IRA for -O0 uses very simple algorithm with usage of very few resources. We could use even simpler method (assigning memory only for all pseudos) but I think it does not worth to do as the generated code will be much bigger and probably will be 1.5-2 times slower.
