RFR: 8315066: Add unsigned bounds and known bits to TypeInt/Long [v17]

[Jatin Bhateja]

On Tue, 10 Sep 2024 12:23:28 GMT, Quan Anh Mai <qamai at openjdk.org> wrote:

>> Hi,
>> 
>> This patch adds unsigned bounds and known bits constraints to TypeInt and TypeLong. This opens more transformation opportunities in an elegant manner as well as helps avoid some ad-hoc rules in Hotspot.
>> 
>> In general, a `TypeInt/Long` represents a set of values `x` that satisfies: `x s>= lo && x s<= hi && x u>= ulo && x u<= uhi && (x & zeros) == 0 && (x & ones) == ones`. These constraints are not independent, e.g. an int that lies in [0, 3] in signed domain must also lie in [0, 3] in unsigned domain and have all bits but the last 2 being unset. As a result, we must canonicalize the constraints (tighten the constraints so that they are optimal) before constructing a `TypeInt/Long` instance.
>> 
>> This is extracted from #15440 , node value transformations are left for later PRs. I have also added unit tests to verify the soundness of constraint normalization.
>> 
>> Please kindly review, thanks a lot.
>> 
>> Testing
>> 
>> - [x] GHA
>> - [x] Linux x64, tier 1-4
>
> Quan Anh Mai has updated the pull request incrementally with one additional commit since the last revision:
> 
>   add doc to TypeInt, rename parameters, remove unused methods

src/hotspot/share/opto/rangeinference.cpp line 75:

> 73:   //      ones  = 1001
> 74:   // zero_violation = 0100, i.e the second bit should be zero, but it is 1 in
> 75:   // lo. Similarly, one_violation = 0001, i.e the forth bit should be one, but

Use LSB (right most) / MSB (left most) terminology. In this case LSB should be one

src/hotspot/share/opto/rangeinference.cpp line 86:

> 84:   }
> 85: 
> 86:   // The principal here is that, consider the first bit in result that is

Suggestion:

  // The principle here is that, consider the first bit in result that is

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PR Review Comment: https://git.openjdk.org/jdk/pull/17508#discussion_r1752284383
PR Review Comment: https://git.openjdk.org/jdk/pull/17508#discussion_r1752285190