bug#39361: continuation and gc performance

[Stefan Israelsson Tampe <stefan.itampe@gmail.com>]

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I think I found a gc leak in guile 3.0

Isn't it so that so the continuation keep a copy of the stack. The issue is
that in the stack a raw integer or float may be present and so the gc
properties is less then ideal as those may be interpreted as pointers by
the GC and lead to parts of the heap being kept from garnage collecting.

The information about a slot being a raw value or a scm value is
available as we do the correct gc updating of the stack inside guile 3.0.
May I propose that we add a bitvector to the continuation that indicate
that if a lslot is raw or not. Then add a pass that collect the rawness
information in the creation of the closure. Finally a custom made mark
procedure for closures can be made that uses all this information to make
sure to mark only scm slots in the stored continuation therby improving gc
perfromance.

With this information it would also be possible to serialize continuations
even if they have slots that are raw values.

Happy Hacking

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