Re: [PATCH] expand description of poly_int conversions

[Richard Sandiford <richard dot sandiford at linaro dot org>]

Martin Sebor <msebor@gmail.com> writes:
> 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?

Not in one go, because you have to specify the intended precision
of the wide_int when constructing it from something like HOST_WIDE_INT.
(That's deliberate.)

>
> 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

Not sure about "a scalar or a wide int", since that implies that wide ints
aren't scalar.  Even more pedantic, sorry, but c1 is an object rather than
a type.

At a higher level, I'm a bit nervous about singling this out as a special
case, since all the poly_int stuff allows HOST_WIDE_INT, offset_int and
wide_int to be combined in the (hopefully) natural way.  E.g. you can
add offset_ints to poly_int64s, assign HOST_WIDE_INTs to poly_offset_ints,
and so on.

But if we do keep it like this, how about:

  @var{c1} must be some form of integer object that can hold all constant
  values of @var{value} without loss of precision; it can be either a normal
  C++ integer or a wide-int class like @code{offset_int}.

?

> +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)

poly_int64

> +@{
> +  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

No need for the extra blank line.

Thanks,
Richard