[gcc r12-8124] libstdc++: shrink-to-fit in std::basic_stacktrace::current(skip, max)

[Jonathan Wakely <redi@gcc.gnu.org>]

https://gcc.gnu.org/g:b2c007b87dcd5db5d59447de2081777aea66f35f

commit r12-8124-gb2c007b87dcd5db5d59447de2081777aea66f35f
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Apr 12 17:17:20 2022 +0100

    libstdc++: shrink-to-fit in std::basic_stacktrace::current(skip, max)
    
    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.

Diff:
---
 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;
       }