On 03/20/2018 05:20 PM, Ivan Gerasimov wrote: > I tried to run it, but the numbers are non-distinguishable for non-zero > arguments. > And my variant performs slightly better with zero argument. > So, I think it's reasonable to keep the variant with the ternary operator.
I am suspicious of this argument. Did you look at the generated code? I get cbnz w10, 0x000003ffa8202384 mov w0, wzr for the zero test and cbz w10, 0x000003ffa81d228c clz w11, w10 orr w10, wzr, #0x80000000 lsr w0, w10, w11 ;*iushr for 42. The branch at the start of both versions goes to a deoptimize trap. We don't want deoptimize traps if we can avoid them, so the branchless version is better IMO. I think your benchmark is of questionable validity because it always uses the same value. This is unlikely in real code. I think the versions should be benchmarked with a *varying* argument. -- Andrew Haley Java Platform Lead Engineer Red Hat UK Ltd. <https://www.redhat.com> EAC8 43EB D3EF DB98 CC77 2FAD A5CD 6035 332F A671
