[patch] canonicalize unsigned [1,MAX] ranges into ~[0,0]
Richard Biener
richard.guenther@gmail.com
Fri Oct 4 16:29:00 GMT 2019
On October 4, 2019 5:38:09 PM GMT+02:00, Jeff Law <law@redhat.com> wrote:
>On 10/4/19 6:59 AM, Aldy Hernandez wrote:
>> When I did the value_range canonicalization work, I noticed that an
>> unsigned [1,MAX] and an ~[0,0] could be two different representations
>> for the same thing. I didn't address the problem then because
>callers
>> to ranges_from_anti_range() would go into an infinite loop trying to
>> extract ~[0,0] into [1,MAX] and []. We had a lot of callers to
>>
>ranges_from_anti_range, and it smelled like a rat's nest, so I bailed.
>>
>> Now that we have one main caller (from the symbolic PLUS/MINUS
>> handling), it's a lot easier to contain. Well, singleton_p also
>calls
>>
>it, but it's already handling nonzero specially, so it wouldn't be affected.
>>
>>
>> With some upcoming cleanups I'm about to post, the fact that [1,MAX]
>and
>> ~[0,0] are equal_p(), but not nonzero_p(), matters. Plus, it's just
>> good form to have one representation, giving us the ability to pick
>at
>> nonzero_p ranges with ease.
>>
>> The code in extract_range_from_plus_minus_expr() continues to be a
>mess
>> (as it has always been), but at least it's contained, and with this
>> patch, it's slightly smaller.
>>
>> Note, I'm avoiding adding a comment header for functions with highly
>> descriptive obvious names.
>>
>> OK?
>>
>> Aldy
>>
>> canonicalize-nonzero-ranges.patch
>>
>> commit 1c333730deeb4ddadc46ad6d12d5344f92c0352c
>> Author: Aldy Hernandez <aldyh@redhat.com>
>> Date: Fri Oct 4 08:51:25 2019 +0200
>>
>> Canonicalize UNSIGNED [1,MAX] into ~[0,0].
>>
>> Adapt PLUS/MINUS symbolic handling, so it doesn't call
>> ranges_from_anti_range with a VR_ANTI_RANGE containing one
>sub-range.
>>
>> diff --git a/gcc/ChangeLog b/gcc/ChangeLog
>> index 6e4f145af46..3934b41fdf9 100644
>> --- a/gcc/ChangeLog
>> +++ b/gcc/ChangeLog
>> @@ -1,3 +1,18 @@
>> +2019-10-04 Aldy Hernandez <aldyh@redhat.com>
>> +
>> + * tree-vrp.c (value_range_base::singleton_p): Use num_pairs
>> + instead of calling vrp_val_is_*.
>> + (value_range_base::set): Canonicalize unsigned [1,MAX] into
>> + non-zero.
>> + (range_has_numeric_bounds_p): New.
>> + (range_int_cst_p): Use range_has_numeric_bounds_p.
>> + (ranges_from_anti_range): Assert that we won't recurse
>> + indefinitely.
>> + (extract_extremes_from_range): New.
>> + (extract_range_from_plus_minus_expr): Adapt so we don't call
>> + ranges_from_anti_range with an anti-range containing only one
>> + sub-range.
>So no problem with the implementation, but I do have a higher level
>question.
>
>One of the goals of the representation side of the Ranger project is to
>drop anti-ranges. Canonicalizing [1, MAX] to ~[0,0] seems to be going
>in the opposite direction. So do we really want to canonicalize to
>~[0,0]?
No, we don't.
Richard.
>jeff
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