Potential performance issue

[Dibyendu Majumdar]

On 15 July 2015 at 20:30, Dibyendu Majumdar <mobile@majumdar.org.uk> wrote:
> Hi Dave,
>
> I have not yet had the time to try out replacing union with struct to
> check performance. Hope to do this soon. But I did try another change
> and was somewhat surprised by the result.
>
> As you know currently I take the address of a Lua stack value and then
> use the pointer to manipulate the value. This is hangover from the
> LLVM port as there it has to be a pointer. But in the libgccjit world,
> we actually do not need the pointer unless the pointer needs to be
> passed to a function. So most of the time we can just work off the
> value array directly.
>
> That is instead of:
>
> (&base[1])->value.tt_
>
> I can just use
> base[1]->value.tt_

I meant base[1].value.tt_ above (sorry for the typo!)

>
> I was hoping that this might help performance somewhat as presumably a
> pointer (going by your change to get_address) may not be optimisable.
> To my surprise however the performance dropped by half after the
> change. So of course I have not committed this change.
>
> This is just an FYI as I don't intend to investigate this right now (I
> have saved the changes so that I can look at this at some time in the
> future).