diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 6768b17ed09c..d991115892ad 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -3,6 +3,9 @@
 	* tree-ssa-dom.c (record_equivalences_from_phis): Speed up by
 	doing a pointer comparison.
 
+	* tree-ssa-dom.c (record_equivalences_from_phis): Add a
+	comment.
+
 2004-12-13  Kazuhiro Inaoka <inaoka.kazuhiro@renesas.com>
 
 	* config/m32r/t-linux (SHLIB_MAPFILES): Add libgcc-glibc.ver to
diff --git a/gcc/tree-ssa-dom.c b/gcc/tree-ssa-dom.c
index def20d6539d7..5c6097939e50 100644
--- a/gcc/tree-ssa-dom.c
+++ b/gcc/tree-ssa-dom.c
@@ -1177,7 +1177,9 @@ record_equivalences_from_phis (basic_block bb)
 	{
 	  tree t = PHI_ARG_DEF (phi, i);
 
-	  /* Ignore alternatives which are the same as our LHS.  */
+	  /* Ignore alternatives which are the same as our LHS.  Since
+	     LHS is a PHI_RESULT, it is known to be a SSA_NAME, so we
+	     can simply compare pointers.  */
 	  if (lhs == t)
 	    continue;