Re: [Bug] OP_SELF uses an unnecessary extra register

[KHMan <keinhong@...>]

On 9/7/2017 9:00 AM, Soni L. wrote:
> On 2017-09-06 03:21 PM, Egor Skriptunoff wrote:
> > On Wed, Sep 6, 2017 at 4:28 PM, Soni L. wrote:
> >
> >     While playing with the Lua parser I noticed OP_SELF uses an
> >     unnecessary extra register, but this is only visible if you
> > have
> >     more than 256 constants.
> >
> >         771    [258]    LOADK        3 -257    ; "print"
> >         772    [258]    SELF         1 1 3
> >
> >
> > This is not a bug.
> > Instruction "SELF 1 1 -257" is impossible due to limitation of 9
> > bits per constant index (operand C) for opcode SELF.
> > On the contrary, LOADK can address any constant using 18-bit
> > field (field Bx).
> > That's why all constants except first 256 have to be passed
> > through intermediate register.
>
> SELF takes 2 inputs and produces 2 outputs, so why's it 1 1 3 and
> not 1 1 2?

Register based virtual machine, is it.  Yes, hmmm. [1]

[1] Sorry, couldn't resist. :-p
Converted using: http://www.yodaspeak.co.uk/index.php

--
Cheers,
Kein-Hong Man (esq.)
Selangor, Malaysia