On 3/11/26 16:51, Andres Freund wrote: > Hi, > > On 2025-11-28 10:00:21 +0100, Daniel Gustafsson wrote: >>> On 28 Nov 2025, at 09:44, Jakub Wartak <[email protected]> >>> wrote: >>> >>> That's a typo in src/include/port/atomics/arch-x86.h, isn't it ?: >>> if defined(__i568__) || defined(__i668__) || /* gcc i586+ */ >>> If yes, then a patch is attached. Not that it harms something or >>> somebody has such old hardware, but I've just spotted it while looking >>> for something else. >> >> That indeed looks like a clear typo, but if noone has complained since 2017 >> then maybe removing the checks is the right course of action? > > Tomas also just found these typos, which made me find this thread. > > These typos are obviously mine. Ugh. > > > I do think we should drop the 32bit support, rather than fixing the typos. > > > While architecturally correct, the 586 indeed can do tear free 8 byte reads / > writes, some quick experiments show that it's actually not entirely trivial to > get the compiler to generate the right code, at least with gcc. > > A volatile 8 byte read / store with gcc only generates correct code when > building with a newer -march= (it's using movq when correct, but it doesn't > start using it with just -mmmx, which added the instruction). For 586 one > needs to get the compiler to use fildq/fistpq, which I could only make happen > when using the atomic builtins / C11 atomics. > > I also just can't get excited about expending any work on performance for > 32bit builds. >
True. Are you suggesting we "drop" the support even in backbranches? AFAIK those never actually supported this due to the typos, so it's not really a change in behavior. regards -- Tomas Vondra
