Re: VRP: abstract out wide int CONVERT_EXPR_P code

[Aldy Hernandez <aldyh@redhat.com>]

On 08/28/2018 05:27 AM, Richard Biener wrote:
> On Mon, Aug 27, 2018 at 2:24 PM Aldy Hernandez <aldyh@redhat.com> wrote:
>>
>> Howdy!
>>
>> Phew, I think this is the last abstraction.  This handles the unary
>> CONVERT_EXPR_P code.
>>
>> It's the usual story-- normalize the symbolics to [-MIN,+MAX] and handle
>> everything generically.
>>
>> Normalizing the symbolics brought about some nice surprises.  We now
>> handle a few things we were punting on before, which I've documented in
>> the patch, but can remove if so desired.  I wrote them mainly for myself:
>>
>> /* NOTES: Previously we were returning VARYING for all symbolics, but
>>      we can do better by treating them as [-MIN, +MAX].  For
>>      example, converting [SYM, SYM] from INT to LONG UNSIGNED,
>>      we can return: ~[0x8000000, 0xffffffff7fffffff].
>>
>>      We were also failing to convert ~[0,0] from char* to unsigned,
>>      instead choosing to return VR_VARYING.  Now we return ~[0,0].  */
>>
>> Tested on x86-64 by the usual bootstrap and regtest gymnastics,
>> including --enable-languages=all, because my past sins are still
>> haunting me.
>>
>> OK?
> 
> The new wide_int_range_convert_tree looks odd given it returns
> tree's.  I'd have expected an API that does the conversion resulting
> in a wide_int range and the VRP code adapting to that by converting
> the result to trees.

Hmmm, yeah.  I agree.  I'll think about this some more and see what I 
can come up with.

Thanks.
Aldy