From 57867881e31273f91c398b55f75417484f11ddc0 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Sat, 9 Nov 2019 10:16:15 -0800
Subject: gc: bugfix: maintain tail pointer in new sweep code.

* gc.c (sweep): The new logic for removing a deleted
heap's blocks from the free list must correctly maintain
free_tail. Whenever a node is deleted which is the tail node,
the tail pointer must move to the parent's tail field, or to
the free_list pointer. We don't need to do anything afterward
for the free_list == 0 case; that is taken care of.
---
 gc.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/gc.c b/gc.c
index b136143a..3460fb27 100644
--- a/gc.c
+++ b/gc.c
@@ -665,13 +665,12 @@ static int_ptr_t sweep(void)
       for (ppf = &free_list; *ppf != nil; ) {
         val block = *ppf;
         if (block >= heap->block && block < end) {
-          *ppf = block->t.next;
+          if ((*ppf = block->t.next) == 0)
+            free_tail = ppf;
         } else {
           ppf = &block->t.next;
         }
       }
-      if (free_list == 0)
-        free_tail = &free_list;
       *pph = heap->next;
       free(heap);
 #if HAVE_VALGRIND
-- 
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