assoc_array: replace the labels in gc's tree walk with a loop

assoc_array_gc() walks the old tree depth first, without recursion,
building the copy as it goes.  Its position is a handful of locals, and
its moves are labels: descend copies a node and the shortcut in front
of it, continue_node goes on through the node's slots, the code after
the fold removes a node holding nothing but a shortcut or a shortcut in
front of a small node, and ascend_old_tree climbs back up.

Keep the walk and its order, but give the position a structure,
struct assoc_array_gc_walk, and each move a function:
assoc_array_gc_copy(), assoc_array_gc_next(), assoc_array_gc_pack() and
assoc_array_gc_ascend().  assoc_array_gc() becomes a loop that copies a
subtree, then finds the next one, packing and climbing past the nodes
that are done.

Finishing is one test now: after packing, a copy has no parent exactly
when it is the whole tree.  That covers all four ways the old code
finished: the three gotos to gc_complete, and the climb out of a node
below a root shortcut that is kept, which now stops at the packing.

The copy is made in one place, so gcc inlines all of it into
assoc_array_gc(), which has no recursion: its stack frame is 152 bytes,
against 128 before, on an x86-64 defconfig.

No functional change.

Assisted-by: LLM
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Tested-by: David Howells <dhowells@redhat.com>
Reviewed-by: David Howells <dhowells@redhat.com>

0 files changed, 0 insertions, 0 deletions