diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index d9f08ed2af88..bd91133b4c74 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,4 +1,10 @@
-2005-03-20  Richard Sandiford  <rsandifo@redhat.com>
+2005-03-30  Richard Sandiford  <rsandifo@redhat.com>
+
+	* doc/options.texi: Document the new MaskExists flag.
+	* opth-gen.awk: Don't output MASK and TARGET macros for Mask(...)
+	if the option has the MaskExists flag.
+
+2005-03-30  Richard Sandiford  <rsandifo@redhat.com>
 
 	* opt-functions.awk (flag_set_p, test_flag): New functions.
 	(switch_flags): Use them.
diff --git a/gcc/doc/options.texi b/gcc/doc/options.texi
index 138ebdb838d9..959f952fc945 100644
--- a/gcc/doc/options.texi
+++ b/gcc/doc/options.texi
@@ -144,6 +144,7 @@ The options-processing script will automatically allocate a unique
 bit for the option and set the macro @code{MASK_@var{name}} to the
 appropriate bitmask.  It will also declare a @code{TARGET_@var{name}}
 macro that has the value 1 when the option is active and 0 otherwise.
+You can disable this behavior using @code{MaskExists}.
 
 @item InverseMask(@var{othername})
 @itemx InverseMask(@var{othername}, @var{thisname})
@@ -152,6 +153,15 @@ The option is the inverse of another option that has the
 the options-processing script will declare a @code{TARGET_@var{thisname}}
 macro that is 1 when the option is active and 0 otherwise.
 
+@item MaskExists
+The mask specified by the @code{Mask} property already exists.
+No @code{MASK} or @code{TARGET} definitions should be added to
+@file{options.h} in response to this option record.
+
+The main purpose of this property is to support synonymous options.
+The first option should use @samp{Mask(@var{name})} and the others
+should use @samp{Mask(@var{name}) MaskExists}.
+
 @item Report
 The state of the option should be printed by @option{-fverbose-asm}.
 
diff --git a/gcc/opth-gen.awk b/gcc/opth-gen.awk
index 3839af9a31c5..d980b12c2837 100644
--- a/gcc/opth-gen.awk
+++ b/gcc/opth-gen.awk
@@ -70,7 +70,7 @@ for (i = 0; i < n_opts; i++) {
 masknum = 0
 for (i = 0; i < n_opts; i++) {
 	name = opt_args("Mask", flags[i])
-	if (name != "")
+	if (name != "" && !flag_set_p("MaskExists", flags[i]))
 		print "#define MASK_" name " (1 << " masknum++ ")"
 }
 if (masknum > 31)
@@ -79,7 +79,7 @@ print ""
 
 for (i = 0; i < n_opts; i++) {
 	name = opt_args("Mask", flags[i])
-	if (name != "")
+	if (name != "" && !flag_set_p("MaskExists", flags[i]))
 		print "#define TARGET_" name \
 		      " ((target_flags & MASK_" name ") != 0)"
 }