On Tue, Aug 6, 2013 at 3:05 PM, <[email protected]> wrote: > On 2013/08/06 12:56:17, Jakob wrote: > >> Unifying lithium codegen and the stub sounds reasonable. Maybe you can do >> a >> microbenchmark to figure out whether the branchless stub code or the >> > conditional > >> "neg" in lithium is faster in practice. >> > If I understand things correctly, we are talking about bit twiddling hacks like http://graphics.stanford.edu/~seander/bithacks.html#IntegerAbs here. A microbenchmark is totally useless, because it doesn't show the higher register pressure due to the additional register needed.
> Actually I did an experiment before. The branchless stub code was faster > than > the conditional "neg". One of my previous idea is to port branchless code > to > lithium. The issue is that LMathAbs only has one available register. To > use the > branchless code, you need to change the LMathAbs instruction to assign a > temporary register. I am not really convinced that trading a branch for an additional register is the right thing to do, my gut feeling is quite the opposite: Better use a branch than wasting a register. -- -- v8-dev mailing list [email protected] http://groups.google.com/group/v8-dev --- You received this message because you are subscribed to the Google Groups "v8-dev" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/groups/opt_out.
