Re: Shrinking the C core

[Ihor Radchenko <yantar92@posteo.net>]

Po Lu <luangruo@yahoo.com> writes:

>> `car' implementation is very unlikely to change in future.
>
> Why not?

Mostly because such basic functions are rarely changed.
Of course, it is not impossible that `car' is changed in future.

>> But `floor' and other functions (we should not be limited to `floor')
>> may change their implementations. The extra "native comp" copy of the
>> implementation will need to be always synchronized with the original
>> implementation. I doubt that it is practical maintenance-wise.
>
> How and why so?  How are Fcar and Ffloor divergent in this department?

`floor' might also be rather stable. I was mostly referring to "we
should not be limited to `floor'" - it may be a problem for other
functions.

But let me rephrase it in other terms: what you propose will require
maintaining two separate implementations of subroutines - one in C, and
one specially tailored to GCC JIT psudocode. This may be doable for a
small set of core primitives, but not scalable if we want to make more
subroutines benefit from GGC JIT optimizations.

Another idea, if rewriting in Elisp is not feasible, could be somehow
structuring the internal C code in such a way that we can derive GCC
JIT pseudocode right from the C function bodies.

For example, Ffloor could be (1) split into smaller functions dedicated
to certain argument type combinations; (2) record a metadata readable by
native comp code about which small function correspond to different
argument types. Then, native comp can emit direct calls to these smaller
(and faster) functions when the type is known.

-- 
Ihor Radchenko // yantar92,
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