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Re: Tcl - compiling

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Will Coleda
October 3, 2005 18:52
Re: Tcl - compiling
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On Oct 3, 2005, at 6:34 PM, Leopold Toetsch wrote:

> On Oct 3, 2005, at 22:57, Will Coleda wrote:
>> 3) Keep a global counter that is incremented whenever a procedure  
>> is created or rename'd. When generating the compiled code, key  
>> against this counter - if it's changed, we must fall back to the  
>> interpreted version. (which, although it starts out with a a call  
>> to the compiled builtin, might have been replaced at that point.).
> I don't see the point. Your compiler can emit, e.g.:
>   "while"(test, body)
> You provide an appropriate implementation of a default "while"  
> function, in your default namespace.
> Whenever user code overrides the "while" word ("set while $foo" -  
> or some such - I dunno Tcl syntax details), you store_global the  
> new implementation as a compiled function into the same namespace  
> (or as a lexical).

That's actually how things work right now (very similar to the  
interpreter from previous versions).

I'm suggesting switching to inlining the code when possible... and  
then watching out for cases where the inlined version is stale (using  
a fairly simple method, but one that'll still give us a boost.). The  
degenerate case using this caching/inlining will be the current  
implementation (plus an integer compare before each invocation)

Is the argument that inlining will not (even theoretically) provide a  
speed boost? I imagine on single pass code it'd be a wash, but for  
something like while, we're potentially avoiding one find_global per  
statement per iteration of the body, as well as the associated call/ 
return for each element in the body. Even for something like examples/ 
bench.tcl, that'd be tens of thousands of parrot sub calls/returns  
that we could potentially eliminate. as low as that overhead is, I  
imagine it's got to add up.

The nice thing about doing the inlining _as it's available_ means  
that (presuming this *is* a good thing), we can inline the builtins  
that give us the best boost first, and I don't have to reimplement  
everything all at once.


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