[gcc r11-11098] libstdc++: Fix std::deque::size() Xmethod [PR112491]

[gcc r11-11098] libstdc++: Fix std::deque::size() Xmethod [PR112491]

[Jonathan Wakely]

https://gcc.gnu.org/g:57727d36e0a3d69dbd6b2221cde0624dbb9dfc95

commit r11-11098-g57727d36e0a3d69dbd6b2221cde0624dbb9dfc95
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Nov 14 15:08:13 2023 +0000

    libstdc++: Fix std::deque::size() Xmethod [PR112491]
    
    The Xmethod for std::deque::size() assumed that the first element would
    be at the start of the first node. That's only true if elements are only
    added at the back. If an element is inserted at the front, or removed
    from the front (or anywhere before the middle) then the first node will
    not be completely populated, and the Xmethod will give the wrong result.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/112491
            * python/libstdcxx/v6/xmethods.py (DequeWorkerBase.size): Fix
            calculation to use _M_start._M_cur.
            * testsuite/libstdc++-xmethods/deque.cc: Check failing cases.
    
    (cherry picked from commit 4db820928065eccbeb725406450d826186582b9f)

Diff:
---
 libstdc++-v3/python/libstdcxx/v6/xmethods.py       | 13 ++++++++-----
 libstdc++-v3/testsuite/libstdc++-xmethods/deque.cc | 20 ++++++++++++++++++++
 2 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/libstdc++-v3/python/libstdcxx/v6/xmethods.py b/libstdc++-v3/python/libstdcxx/v6/xmethods.py
index d6cbcf139c5..5223cce76ca 100644
--- a/libstdc++-v3/python/libstdcxx/v6/xmethods.py
+++ b/libstdc++-v3/python/libstdcxx/v6/xmethods.py
@@ -168,11 +168,14 @@ class DequeWorkerBase(gdb.xmethod.XMethodWorker):
         self._bufsize = 512 // val_type.sizeof or 1
 
     def size(self, obj):
-        first_node = obj['_M_impl']['_M_start']['_M_node']
-        last_node = obj['_M_impl']['_M_finish']['_M_node']
-        cur = obj['_M_impl']['_M_finish']['_M_cur']
-        first = obj['_M_impl']['_M_finish']['_M_first']
-        return (last_node - first_node) * self._bufsize + (cur - first)
+        start = obj['_M_impl']['_M_start']
+        finish = obj['_M_impl']['_M_finish']
+        if not start['_M_node']:
+            return 0
+        return (self._bufsize
+                * (finish['_M_node'] - start['_M_node'] - 1)
+                + (finish['_M_cur'] - finish['_M_first'])
+                + (start['_M_last'] - start['_M_cur']))
 
     def index(self, obj, idx):
         first_node = obj['_M_impl']['_M_start']['_M_node']
diff --git a/libstdc++-v3/testsuite/libstdc++-xmethods/deque.cc b/libstdc++-v3/testsuite/libstdc++-xmethods/deque.cc
index b29e1a0abca..1dd0bd8d875 100644
--- a/libstdc++-v3/testsuite/libstdc++-xmethods/deque.cc
+++ b/libstdc++-v3/testsuite/libstdc++-xmethods/deque.cc
@@ -67,6 +67,26 @@ main ()
 // { dg-final { whatis-test q1.back() int } }
 // { dg-final { whatis-test q3\[0\] int } }
 
+  // PR libstdc++/112491
+  std::deque<int> q5;
+  q5.push_front(0);
+// { dg-final { note-test q5.size() 1 } }
+  std::deque<int> q6 = q1;
+  q6.pop_front();
+// { dg-final { note-test {q6.size() == (q1_size-1)} true } }
+  std::deque<int> q7 = q2;
+  q7.pop_front();
+  q7.pop_front();
+// { dg-final { note-test {q7.size() == (q2_size-2)} true } }
+  std::deque<int> q8 = q3;
+  q8.pop_front();
+  q8.pop_front();
+  q8.pop_front();
+// { dg-final { note-test {q8.size() == (q3_size-3)} true } }
+  std::deque<int> q9 = q8;
+  q9.clear();
+// { dg-final { note-test q9.size() 0 } }
+
   return 0;  // Mark SPOT
 }