diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 89cfc69240a..0267508f20d 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2007-07-03  Eric Christopher  <echristo@apple.com>
+
+	* doc/cppopts.texi: Add conflicting option note to -dM.
+	* doc/invoke.texi: Add note about possible conflicts with
+	-E for -dCHARS and note that -dM will not produce
+	any results if there is no machine dependent reorg.
+	
 2007-07-03  Geoffrey Keating  <geoffk@apple.com>
 
 	* tree.h (DECL_ALIGN): Back out previous change.
diff --git a/gcc/doc/cppopts.texi b/gcc/doc/cppopts.texi
index 17235bdae58..73db8323e61 100644
--- a/gcc/doc/cppopts.texi
+++ b/gcc/doc/cppopts.texi
@@ -641,6 +641,10 @@ touch foo.h; cpp -dM foo.h
 @noindent
 will show all the predefined macros.
 
+If you use @option{-dM} without the @option{-E} option, @option{-dM} is
+interpreted as a synonym for @option{-fdump-rtl-mach}.
+@xref{Debugging Options, , ,gcc}.
+
 @item D
 @opindex dD
 Like @samp{M} except in two respects: it does @emph{not} include the
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 2b5fff22014..57dbb025d08 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -4270,7 +4270,9 @@ Says to make debugging dumps during compilation at times specified by
 compiler.  The file names for most of the dumps are made by appending a
 pass number and a word to the @var{dumpname}.  @var{dumpname} is generated
 from the name of the output file, if explicitly specified and it is not
-an executable, otherwise it is the basename of the source file.
+an executable, otherwise it is the basename of the source file. These
+switches may have different effects when @option{-E} is used for
+preprocessing.
 
 Most debug dumps can be enabled either passing a letter to the @option{-d}
 option, or with a long @option{-fdump-rtl} switch; here are the possible
@@ -4407,7 +4409,7 @@ Dump after modulo scheduling, to @file{@var{file}.136r.sms}.
 @opindex dM
 @opindex fdump-rtl-mach
 Dump after performing the machine dependent reorganization pass, to
-@file{@var{file}.155r.mach}.
+@file{@var{file}.155r.mach} if that pass exists.
 
 @item -dn
 @itemx -fdump-rtl-rnreg