On 3/8/19 2:58 PM, Jan Hubicka wrote: >> On 3/8/19 1:44 PM, Jan Hubicka wrote: >>>> Hi. >>>> >>>> Thanks to Intel guys, we've done some re-measurement in PR86952 >>>> about usage of jump tables when retpolines are used. >>>> Numbers prove that disabling of JT should be the best for now. >>>> >>>> Patch can bootstrap on x86_64-linux-gnu and survives regression tests. >>>> >>>> Ready to be installed? >>> >>> OK, thanks! >>> I wonder if there is some threshold for extremely large jumptables where >>> branchy sequence will loose, but I think it is better to disable them >>> than what we have right now. >> >> I tested switch statements up to 4096 and it was still slower ;) > > Well, we have switch statements with this many cases in > insn-attrtab/latencytab tables. I suppose what kind of code you compile > with retpolines, but I would expect even bigger switch statements to > appear in real code (large DFA automatons and such)
Question is whether you'll meet such huge switch statements in Linux kernel? Martin > > Honza >> >> Martin >> >>> >>> Honza >>> >>
