Re: copymemory basic question

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Tony Proctor wrote:
> Although I haven't checked what the VB compiler generates, 'static'
> variables are generally slower in other languages, and for the same
> basic reason: it's the way they're addressed rather than the way
> they're stored or created.

I'd agree with that assessment and your description of the process except that in the particular case that started this subthread, there were no stack variables at all, which means that the function prolog can be skipped. When this is the case, a single static variable ought to be measurably more efficient in a tiny function like this one. The difference between "mov eax, [staticvar]" and "mov eax, [epb-8]" is insignificant.

(I believe TLS is addressed off FS, which would make that "mov eax, FS:[staticvar]", still a minor hit compared to the call to set up a frame.)

What we don't know is whether VB does indeed skip the prolog/epilog when it can. If it doesn't, then there's no advantage (and a slight disadvantage) to using static locals. From the timings, it sure looks as if it doesn't.

--
Jim
.

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