expand description of poly_int conversions

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

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

On 02/26/2018 12:45 PM, Richard Sandiford wrote:
> 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}.
>
> ?

Sure.  Attached is an update with your change.

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)
@@ -836,8 +836,23 @@ 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} 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}.  The following example illustrates using
+the function to convert a @code{poly_int64} to @code{HOST_WIDE_INT}
+and to @code{offset_int}.
+@smallexample
+void f (poly_int64 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.

Martin Sebor <msebor@gmail.com> writes:
> On 02/26/2018 12:45 PM, Richard Sandiford wrote:
>> 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}.
>>
>> ?
>
> Sure.  Attached is an update with your change.

LGTM (but I can't approve).

Thanks,
Richard

On 02/26/2018 02:09 PM, Richard Sandiford wrote:
> Martin Sebor <msebor@gmail.com> writes:
>> On 02/26/2018 12:45 PM, Richard Sandiford wrote:
>>> 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}.
>>>
>>> ?
>>
>> Sure.  Attached is an update with your change.
> 
> LGTM (but I can't approve).
That, IMHO, is a technicality :-)  You know these bits better than
anyone.  So if you're OK with them, that's good enough for me :-)

Rubber-stamped for the trunk.


jeff