On Sat, Dec 9, 2017 at 1:29 AM, David Laight <david.lai...@aculab.com> wrote: > From: Xin Long ... >> Hi, David, Sorry, I'm not sure we're worrying about the cpu cost or >> codes style now ? >> >> For cpu cost, I think 0x848(%r13) operation must be better than the >> generated code of if-else. > > Nope - the call xxx(%ryyy) is likely to be a data cache miss and a complete > cpu pipeline stall. > > The conditional will be a data cache hit and the code (for one branch) > will be prefetched and speculatively executed. > > Some very modern cpu might manage to predict indirect jumps, but for > most it is a full pipeline stall. Thanks for the CPU information.
The thing is with if-else can't avoid xxx(%ryyy) in this case, as Marcelo said above. It seems if-else will just be a extra cost compare to this one.
