[gcc r14-8890] libstdc++: Add comment to gslice::operator=(const gslice&) [PR100147]

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

https://gcc.gnu.org/g:4e5dc6d9686a34d446147b923fe838389758a512

commit r14-8890-g4e5dc6d9686a34d446147b923fe838389758a512
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Sun Feb 4 21:39:11 2024 +0000

    libstdc++: Add comment to gslice::operator=(const gslice&) [PR100147]
    
    There's no need to check for self-assignment here, it would just add
    extra code for an unlikely case. Add a comment saying so.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/100147
            * include/bits/gslice.h (operator=): Add comment about lack of
            self-assignment check.

Diff:
---
 libstdc++-v3/include/bits/gslice.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/libstdc++-v3/include/bits/gslice.h b/libstdc++-v3/include/bits/gslice.h
index 3d78da2bd754..d9a8b929a571 100644
--- a/libstdc++-v3/include/bits/gslice.h
+++ b/libstdc++-v3/include/bits/gslice.h
@@ -169,6 +169,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   inline gslice&
   gslice::operator=(const gslice& __g)
   {
+    // Safe for self-assignment. Checking for it would add overhead just to
+    // optimize a case that should never happen anyway.
     if (__g._M_index)
       __g._M_index->_M_increment_use();
     if (_M_index && _M_index->_M_decrement_use() == 0)