[PATCH 3/5] libstdc++: keep subtree sizes in pb_ds binary search trees (PR 81806)

[Xi Ruoyao <xry111@mengyan1223.wang>]

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> The second and third patch together resolve PR 81806.

The attached patch modifies split_finish to use the subtree size we maintained
in the previous patch, resolving libstdc++/81806.

libstdc++-v3/ChangeLog:

	PR libstdc++/81806
	* include/ext/pb_ds/detail/bin_search_tree_/split_join_fn_imps.hpp
	  (split_finish): Use maintained size, instead of calling
	  std::distance.
-- 
Xi Ruoyao <xry111@mengyan1223.wang>
School of Aerospace Science and Technology, Xidian University

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From 4434da1b2b45797204f4fd978dcc4fbba4b17c6e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?X=E2=84=B9=20Ruoyao?= <xry111@mengyan1223.wang>
Date: Fri, 10 Jul 2020 21:38:09 +0800
Subject: [PATCH 3/5] libstdc++: use maintained size when split pb_ds binary
 search trees

libstdc++-v3/ChangeLog:

	PR libstdc++/81806
	* include/ext/pb_ds/detail/bin_search_tree_/split_join_fn_imps.hpp
	  (split_finish): Use maintained size, instead of calling
	  std::distance.
---
 .../ext/pb_ds/detail/bin_search_tree_/split_join_fn_imps.hpp  | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/ext/pb_ds/detail/bin_search_tree_/split_join_fn_imps.hpp b/libstdc++-v3/include/ext/pb_ds/detail/bin_search_tree_/split_join_fn_imps.hpp
index d08288f186d..fb924b4434b 100644
--- a/libstdc++-v3/include/ext/pb_ds/detail/bin_search_tree_/split_join_fn_imps.hpp
+++ b/libstdc++-v3/include/ext/pb_ds/detail/bin_search_tree_/split_join_fn_imps.hpp
@@ -133,7 +133,9 @@ PB_DS_CLASS_C_DEC::
 split_finish(PB_DS_CLASS_C_DEC& other)
 {
   other.initialize_min_max();
-  other.m_size = std::distance(other.begin(), other.end());
+  other.m_size = 0;
+  if (other.m_p_head->m_p_parent != 0)
+    other.m_size = other.m_p_head->m_p_parent->m_subtree_size;
   m_size -= other.m_size;
   initialize_min_max();
   PB_DS_ASSERT_VALID((*this))
-- 
2.27.0