Re: [Sablevm-user] SableVM question

[Etienne M. G. <eg...@j-...>]

Hi Marcel.

I'm sorry for the delay; I had a pretty hectic day.

Marcel Ammerlaan wrote:
> My question is: why use goto instead of switch()?

The concept of using goto's in the interpreter loop is usually referred
to as "threaded" interpretation.  This name originates, if I am right,
from implementations of the FORTH language.

The short answer to your question is: because it's (usually) much
faster.  But, your experiment suggests that this is not the case...  I
would be very interested in looking at your small benchmark program, to
see if there's something wrong with it.  Would it be possible to send a
copy of it on the list?  (This shouldn't be a long program, I guess).

The reason "labels as values" were added in gcc was explicitly for cases
like interpreter loops.  Here's some excerpt from gcc's documentation:

"Another use of label values is in an interpreter for threaded code. 
The labels within the interpreter function can be stored in the threaded
code for super-fast dispatching."

Cheers,

Etienne
-- 
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Etienne M. Gagnon, M.Sc.                     e-mail: eg...@j-...
Author of SableVM:                             http://www.sablevm.org/
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