Index: cppopts.texi
===================================================================
--- cppopts.texi	(revision 126262)
+++ cppopts.texi	(working copy)
@@ -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
Index: invoke.texi
===================================================================
--- invoke.texi	(revision 126262)
+++ invoke.texi	(working copy)
@@ -4270,7 +4270,9 @@ Says to make debugging dumps during comp
 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{@
 @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