Re: Pure nil and t?

[Andreas Schwab]

David Kastrup <address@hidden> writes:

> Dmitry Antipov <address@hidden> writes:
>
>> For a long byte-compile runs, ~15-17% of objects seen by GC are nil and t
>> (especially nil, which is ~10x more "popular" than t).  What about making
>> them pure?  Thus way they will be quickly filtered out by PURE_POINTER_P
>> check in mark_object, thus offloading GC from an in-depth examination of
>> them each time when they're found.
>
> In my Emacs I see
> M-: (symbol-plist nil) RET
> (event-symbol-element-mask (nil 0) event-symbol-elements (nil) modifier-cache 
> ((0)))
> M-: (symbol-plist t) RET
> (event-symbol-element-mask (t 0) event-symbol-elements (t) modifier-cache ((0 
> . t)))
>
> While I consider it likely that those are the result of glitches and/or
> bugs, it would be nice if those glitches did not lead to crashes by
> letting these plists get collected in spite of being accessible.

They probably would have to be made pure as well, and checks would have
to be added to not try to modify any of the fields of a pure symbol.

Andreas.

-- 
Andreas Schwab, SUSE Labs, address@hidden
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."