[committed 4/5] libstdc++: shrink-to-fit in std::basic_stacktrace::current(skip, max)

[Jonathan Wakely via Gcc-patches]

Tested powerpc64-linux, pushed to trunk.

-- >8 --

If a large stacktrace is reduced to a max depth that is less than half
the capacity it will now be reallocated to remove the unused capacity.

libstdc++-v3/ChangeLog:

        * include/std/stacktrace (basic_stacktrace::current): Reallocate
        a smaller container if the unused capacity is larger than the
        used size.
---
 libstdc++-v3/include/std/stacktrace | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/std/stacktrace 
b/libstdc++-v3/include/std/stacktrace
index 382d900a822..98ce9231150 100644
--- a/libstdc++-v3/include/std/stacktrace
+++ b/libstdc++-v3/include/std/stacktrace
@@ -289,7 +289,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
            if (__err < 0)
              __ret._M_clear();
            else if (__ret.size() > __max_depth)
-             __ret._M_impl._M_resize(__max_depth, __ret._M_alloc);
+             {
+               __ret._M_impl._M_resize(__max_depth, __ret._M_alloc);
+
+               if (__ret._M_impl._M_capacity / 2 >= __max_depth)
+                 {
+                   // shrink to fit
+                   _Impl __tmp = __ret._M_impl._M_clone(__ret._M_alloc);
+                   if (__tmp._M_capacity)
+                     {
+                       __ret._M_clear();
+                       __ret._M_impl = __tmp;
+                     }
+                 }
+             }
          }
        return __ret;
       }
-- 
2.34.1