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[decycler] Reduce stack use

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Down from 5 pointers to 4.
This commit is contained in:
Behdad Esfahbod 2025-02-17 14:49:06 -07:00
parent 5aea89b5c4
commit 646da80c41
1 changed files with 14 additions and 12 deletions
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26
src/hb-decycler.hh
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@ -58,13 +58,12 @@
* There are three method's:
*
* - hb_decycler_node_t() constructor: Creates a new node in the traversal.
* The constructor takes a reference to the decycler object and takes a
* snapshot of it, and advances the hare pointer, and for every other
* descent, advances the tortoise pointer.
* The constructor takes a reference to the decycler object and inserts
* itself as the latest node in the traversal path, by advancing the hare
* pointer, and for every other descent, advancing the tortoise pointer.
*
* - ~hb_decycler_node_t() destructor: Restores the decycler object to the
* snapshot taken in the constructor, effectively removing the node from
* the traversal path.
* - ~hb_decycler_node_t() destructor: Restores the decycler object to its
* previous state by removing the node from the traversal path.
*
* - bool visit(unsigned value): Called on every node in the graph. Returns
* true if the node is not part of a cycle, and false if it is. The value
@ -92,8 +91,6 @@ struct hb_decycler_node_t
hb_decycler_node_t (hb_decycler_t &decycler)
: decycler (decycler)
{
snapshot = decycler;
if (!decycler.tortoise)
{
// First node.
@ -102,6 +99,7 @@ struct hb_decycler_node_t
}
tortoise_asleep = !decycler.hare->tortoise_asleep;
this->prev = decycler.hare;
decycler.hare->next = this;
decycler.hare = this;
@ -111,9 +109,13 @@ struct hb_decycler_node_t
~hb_decycler_node_t ()
{
decycler = snapshot;
if (decycler.hare)
decycler.hare->next = nullptr;
assert (decycler.hare == this);
decycler.hare = prev;
if (prev)
prev->next = nullptr;
if (!tortoise_asleep)
decycler.tortoise = decycler.tortoise->prev;
}
bool visit (unsigned value_)
@ -131,8 +133,8 @@ struct hb_decycler_node_t
private:
hb_decycler_t &decycler;
hb_decycler_t snapshot;
hb_decycler_node_t *next = nullptr;
hb_decycler_node_t *prev = nullptr;
unsigned value = (unsigned) -1;
bool tortoise_asleep = false;
};