--- old/src/cpu/x86/vm/x86_64.ad	2012-03-12 16:31:27.406982700 +0100
+++ new/src/cpu/x86/vm/x86_64.ad	2012-03-12 16:31:26.762945800 +0100
@@ -1714,6 +1714,14 @@
   if (!has_match_rule(opcode))
     return false;
 
+  switch (opcode) {
+    case Op_PopCountI:
+    case Op_PopCountL:
+      if (!UsePopCountInstruction)
+        return false;
+    break;
+  }
+
   return true;  // Per default match rules are supported.
 }