Re: Excessive use of `eassert`

[Paul Eggert]

On 2024-01-19 11:42, Alan Mackenzie wrote:

> On Fri, Jan 19, 2024 at 17:02:06 +0200, Eli Zaretskii wrote:

> > make_fixnum is a trivial bit-shuffling, whereas make_lisp_symbol is
> > much trickier.  Perhaps especially so now that we have
> > symbols-with-positions as well as bare symbols.
>
> Not really.  Symbols with positions don't belong in the obarray.  If they
> somehow get there, then that's a bug to be fixed.

The problem here isn't calling make_lisp_symbol to make symbols with 
positions. It's that Qnil expands to builtin_lisp_symbol (0) which calls 
make_lisp_symbol (&lispsym[0]) which calls XSYMBOL, and XSYMBOL is 
significantly slower now that we have symbols-with-positions, even when 
it is applied to a bare symbol - and this is particularly true with 
--enable-checking and the eassert Stefan mentioned.

I looked into this a bit and installed the attached patches which should 
speed things slightly even with a default build. The main goal was to 
speed up debugging builds, though.

When I built with --enable-checking this seemed to help significantly on 
Ubuntu 23.10 x86-64 with GCC 13.2 -O2 (at least looking at the machine 
code; I didn't benchmark). This depends on compiler and platform so it'd 
be helpful if Stefan could try it out on his machine and see whether it 
helps his cases' performance.

0001-Simplify-and-tune-XSYMBOL.patch
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0002-Speed-up-make_lisp_symbol-when-debugging.patch
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