From 8dbb60b8dfc642a81f1c41fde11767150e8f91a5 Mon Sep 17 00:00:00 2001
From: Jonathan Wakely <jwakely@redhat.com>
Date: Tue, 8 Feb 2022 13:41:33 +0000
Subject: [PATCH] libstdc++: Add comment to acinclude.m4

libstdc++-v3/ChangeLog:

	* acinclude.m4 (GLIBCXX_ENABLE_LOCK_POLICY): Add comment about
	checking for CAS on correct word size.
---
 libstdc++-v3/acinclude.m4 | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
index 7cc52f4db96..f53461c85a5 100644
--- a/libstdc++-v3/acinclude.m4
+++ b/libstdc++-v3/acinclude.m4
@@ -3609,6 +3609,8 @@ AC_DEFUN([GLIBCXX_ENABLE_LOCK_POLICY], [
     ac_save_CXXFLAGS="$CXXFLAGS"
 
     dnl Why do we care about 2-byte CAS on targets with 4-byte _Atomic_word?!
+    dnl Why don't we check 8-byte CAS for sparc64, where _Atomic_word is long?!
+    dnl New targets should only check for CAS for the _Atomic_word type.
     AC_TRY_COMPILE([
     #if ! defined __GCC_HAVE_SYNC_COMPARE_AND_SWAP_2
     # error "No 2-byte compare-and-swap"