--- a/doc/makefile-variables.txt	Thu Apr 11 09:31:09 2013 -0700
+++ b/doc/makefile-variables.txt	Thu Apr 11 10:40:20 2013 -0700
@@ -89,3 +89,8 @@
   default is "/usr"; set it if some other value (e.g., "/usr/gnu") is needed.
 * CONFIGURE_SCRIPT should be set if the default "$(SOURCE_DIR)/configure" is
   unsuitable for whatever reason.
+
+* studio_OPT has a default value of "-xO4".  Occasional bugs in the optimizer
+  have been found which have required altering this to "-xO3".  There are also
+  studio_OPT.$(MACH).$(BITS) versions of this available if greater specificity
+  is needed.