Even if here there is no need for performance, a conditional mov which is not taken is always faster than an unconditional mov (on well optimized cores, it will take 0 cycles).
On Thu, Nov 7, 2013 at 9:10 AM, <[email protected]> wrote: > Thanks for the code review! Responses inline. > > > On 2013/11/07 08:43:23, vincent.belliard.fr wrote: > >> https://codereview.chromium.org/62293002/diff/1/src/arm/ >> lithium-codegen-arm.cc >> File src/arm/lithium-codegen-arm.cc (right): >> > > > https://codereview.chromium.org/62293002/diff/1/src/arm/ > lithium-codegen-arm.cc#newcode773 > >> src/arm/lithium-codegen-arm.cc:773: Register scratch = scratch0(); >> May be you can leave the case FLAG_deopt_every_n_times == 1. It really >> > generates > >> less code for this special case. >> > > I was considering this, but if you want to deoptimize every time, then a > few > extra instructions should not matter much. Moreover, I am told this is > only used > in fuzzing tests, so performance is not really important here. Or is there > a use > case I am not aware of? > > > > https://codereview.chromium.org/62293002/diff/1/src/arm/ > lithium-codegen-arm.cc#newcode778 > >> src/arm/lithium-codegen-arm.cc:778: __ mov(scratch, Operand::Zero()); >> You can also make this mov conditional (you must negate the condition). >> > > I am wondering if it would make any difference in performance. If yes, > which > way? (Not that it matters, the code is for correctness testing). > > > > https://codereview.chromium.org/62293002/diff/1/src/arm/ > lithium-codegen-arm.cc#newcode799 > >> src/arm/lithium-codegen-arm.cc:799: // to use 'msr' and 'mrs' >> instructions >> > here, > >> but they are not supported by >> mrs and msr are available (assembler-arm.h line 1029). >> > > Yes, they are available in the assembler, but our ARM simulator > (simulator-arm.cc) does not know them, Simulator::DecodeType01() fails at > simulator-arm.cc:2247. > > > https://codereview.chromium.org/62293002/ > -- -- 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.
