libstdc++: Do not allocate a zero-size vector<bool> [PR 100153]

The vector<bool>::shrink_to_fit() implementation will allocate new
storage even if the vector is empty. That then leads to the
end-of-storage pointer being non-null and equal to the _M_start._M_p
pointer, which means that _M_end_addr() has undefined behaviour.

The fix is to stop doing a useless zero-sized allocation in
shrink_to_fit(), so that _M_start._M_p and _M_end_of_storage are both
null after an empty vector shrinks.

Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
libstdc++-v3/ChangeLog:

	PR libstdc++/100153
	* include/bits/vector.tcc (vector<bool>::_M_shrink_to_fit()):
	When size() is zero just deallocate and reset.

(cherry picked from commit 681707ec28d56494fa61a80c62500724d55f8586)

diff --git a/libstdc++-v3/include/bits/vector.tcc b/libstdc++-v3/include/bits/vector.tcc
index 27e63388feb1f950187a756b52ae753b29715f86..c49884ade1298b19e4b809e5bbecc5a2f50be5f2 100644 (file)
--- a/libstdc++-v3/include/bits/vector.tcc
+++ b/libstdc++-v3/include/bits/vector.tcc
@@ -944,7 +944,13 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        return false;
       __try
        {
-         _M_reallocate(size());
+         if (size_type __n = size())
+           _M_reallocate(__n);
+         else
+           {
+             this->_M_deallocate();
+             this->_M_impl._M_reset();
+           }
          return true;
        }
       __catch(...)