Re: Shrinking the C core

[<tomas@tuxteam.de>]

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On Sun, Aug 20, 2023 at 09:52:17AM +0200, Emanuel Berg wrote:
> Ihor Radchenko wrote:
> 
> > If we talk about type checking, Elisp uses dynamic typing
> > and compilation cannot do much about it. Native compilation
> > also does not touch C subroutines - the place where
> > typechecks are performed.
> 
> So our typechecks are not optimized, as we can native compile
> Elisp but not C.
> 
> Worse, with dynamic typing they have to be used repeatedly and
> during execution /o\
> 
> Point taken - but we are compiling the C subroutines so in
> theory optimization of typechecks could happen there [...]

I humbly suggest you read up a bit on compilation. Those
type checks happen at compile time for a reason: the very
expensive data flow analysis provides the compiler with
information which is quite difficult to obtain later.

If you /know/ that some x will always be a nonnegative
integer (because every path leading to your execution
node either sets it to zero or increments it, for example),
you can do away with that test and else branch:

  (if (> x 0)
    ...
   ...)

but for that you have to take your program painstakingly
apart into basic blocks, take note of what leads to where
and think hard about which variables are munged where.

That's why modern browsers come with more than one compiler:
the price of that painstaking process is so high that you
want to start quick and dirty (and slow) and focus on those
things which really need attention.

See [1] for a discussion in Guile's context.

Cheers

[1] https://wingolog.org/archives/2020/06/03/a-baseline-compiler-for-guile

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t

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