[PATCH] expand description of poly_int conversions

[Martin Sebor <msebor at gmail dot com>]

Richard,

If you agree, I'd like to update the conversion section of
the poly_int manual to make the conversion to make it clearer
that the to_constant() function can be used even with class
types like offset_int besides scalars.

Also, when testing this I also tried converting poly64_int
into wide_int but that doesn't work.  Is there a way to do
that?

Thanks
Martin

gcc/ChangeLog:

	* doc/poly-int.texi (is_constant): Expand.

Index: gcc/doc/poly-int.texi
===================================================================
--- gcc/doc/poly-int.texi	(revision 258004)
+++ gcc/doc/poly-int.texi	(working copy)
@@ -836,9 +836,24 @@ Return true if @code{poly_int} @var{value} is a co
 
 @item @var{value}.is_constant (&@var{c1})
 Return true if @code{poly_int} @var{value} is a compile-time constant,
-storing it in @var{c1} if so.  @var{c1} must be able to hold all
-constant values of @var{value} without loss of precision.
+storing it in @var{c1} if so.  @var{c1} may be a scalar or a wide int
+class type capable of holding all constant values of @var{value} without
+loss of precision.  The following example illustrates using the function
+to convert a @code{poly64_int} to @code{HOST_WIDE_INT} and to
+@code{offset_int}.
+@smallexample
+void f (poly64_int pi)
+@{
+  HOST_WIDE_INT hwi;
+  if (pi.is_constant (&hwi))
+    ; // Use hwi...
+  offset_int off;
+  if (pi.is_constant (&off))
+    ; // Use off...
+@}
+@end smallexample
 
+
 @item @var{value}.to_constant ()
 Assert that @var{value} is a compile-time constant and return its value.
 When using this function, please add a comment explaining why the