+define_commit_slab(saved_parents, struct commit_list *);
+
+#define EMPTY_PARENT_LIST ((struct commit_list *)-1)
+
+/*
+ * You may only call save_parents() once per commit (this is checked
+ * for non-root commits).
+ */
+static void save_parents(struct rev_info *revs, struct commit *commit)
+{
+ struct commit_list **pp;
+
+ if (!revs->saved_parents_slab) {
+ revs->saved_parents_slab = xmalloc(sizeof(struct saved_parents));
+ init_saved_parents(revs->saved_parents_slab);
+ }
+
+ pp = saved_parents_at(revs->saved_parents_slab, commit);
+
+ /*
+ * When walking with reflogs, we may visit the same commit
+ * several times: once for each appearance in the reflog.
+ *
+ * In this case, save_parents() will be called multiple times.
+ * We want to keep only the first set of parents. We need to
+ * store a sentinel value for an empty (i.e., NULL) parent
+ * list to distinguish it from a not-yet-saved list, however.
+ */
+ if (*pp)
+ return;
+ if (commit->parents)
+ *pp = copy_commit_list(commit->parents);
+ else
+ *pp = EMPTY_PARENT_LIST;
+}
+
+static void free_saved_parents(struct rev_info *revs)
+{
+ if (revs->saved_parents_slab)
+ clear_saved_parents(revs->saved_parents_slab);
+}
+
+struct commit_list *get_saved_parents(struct rev_info *revs, const struct commit *commit)
+{
+ struct commit_list *parents;
+
+ if (!revs->saved_parents_slab)
+ return commit->parents;
+
+ parents = *saved_parents_at(revs->saved_parents_slab, commit);
+ if (parents == EMPTY_PARENT_LIST)
+ return NULL;
+ return parents;
+}
+