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.

diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
index 7cc52f4..f53461c 100644 (file)
--- 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"