diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index d248a107b6f5e..ce38dbac62898 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2014-09-03  Richard Sandiford  <rdsandiford@googlemail.com>
+
+	* doc/rtl.texi (RTX_AUTOINC): Document that the first operand is
+	the automodified register.
+
 2014-09-03  Richard Sandiford  <rdsandiford@googlemail.com>
 
 	* output.h (get_some_local_dynamic_name): Declare.
diff --git a/gcc/doc/rtl.texi b/gcc/doc/rtl.texi
index 605a5a18734d0..44170d2570dc3 100644
--- a/gcc/doc/rtl.texi
+++ b/gcc/doc/rtl.texi
@@ -193,7 +193,8 @@ An RTX code for something that matches in insns, such as
 
 @item RTX_AUTOINC
 An RTX code for an auto-increment addressing mode, such as
-@code{POST_INC}.
+@code{POST_INC}.  @samp{XEXP (@var{x}, 0)} gives the auto-modified
+register.
 
 @item RTX_EXTRA
 All other RTX codes.  This category includes the remaining codes used