Request for Reviews (S): JDK-8003585 strength reduce or eliminate range checks for power-of-two sized arrays

[Roland Westrelin]

Thanks for taking another look at this, Vladimir.

> I know it is duplication but CmpU creation should be under conditions otherwise you are creating and transforming dead node.
> 
> +     Node* ncmp = phase->transform(new CmpUNode(cmp1, cmp2));
> +     if (_test._test == BoolTest::le || _test._test == BoolTest::eq) {
> 
> The test does not cover next conversions:
> 
> +   // Change (arraylength <= 0) or (arraylength == 0)
> +   //   into (arraylength u<= 0)
> +   // Also change (arraylength != 0) into (arraylength u> 0)

Here is a new webrev:

http://cr.openjdk.java.net/~roland/8003585/webrev.02/

Roland.

> 
> Thanks,
> Vladimir
> 
> On 1/7/16 1:29 AM, Roland Westrelin wrote:
>> Can I get a review for this?
>> 
>> Roland.
>> 
>>> On Oct 5, 2015, at 12:51 PM, Roland Westrelin <roland.westrelin at oracle.com> wrote:
>>> 
>>> Here is a new webrev:
>>> 
>>> http://cr.openjdk.java.net/~roland/8003585/webrev.01/
>>> 
>>> Roland.
>>> 
>>>> On Oct 2, 2015, at 3:30 PM, Roland Westrelin <roland.westrelin at oracle.com> wrote:
>>>> 
>>>> Hi Chris,
>>>> 
>>>>> Thanks for picking it up! It mostly looks good to me. (Not a Reviewer)
>>>> 
>>>> Thanks for looking at this again.
>>>> 
>>>>> What I really needed with my earlier webrev was some instructions as to what test to write -- since the Java corelibs can come across this optimization a lot (e.g. HashMap), I didn't have a good idea of what kind of test really needs to be written.
>>>>> 
>>>>> A couple of issues with this webrev:
>>>>> 
>>>>> 1. In subnode.cpp, line 1346:
>>>>> 
>>>>> 1344     } else if (_test._test == BoolTest::lt &&
>>>>> 1345                cmp2->Opcode() == Op_AddI &&
>>>>> 1346                cmp2->in(2)->find_int_con(1)) {
>>>>> 1347       bound = cmp2->in(1);
>>>>> 1348     }
>>>>> 
>>>>> I think it should be
>>>>> cmp2->in(2)->find_int_con(0) == 1
>>>>> instead, because the value passed into this function is actually for a "fallback when no int constant is found". Passing the expected value (1) to it defeats the purpose.
>>>> 
>>>> You’re right. Thanks for spotting that.
>>>> 
>>>>> jint find_int_con(jint value_if_unknown) const {
>>>>>   const TypeInt* t = find_int_type();
>>>>>   return (t != NULL && t->is_con()) ? t->get_con() : value_if_unknown;
>>>>> }
>>>>> 
>>>>> 2. Formattign nitpick: could you please trim the spaces before the new's on lines 1368, 1369 and 1387
>>>> 
>>>> Sure.
>>>> 
>>>> I’ll send an updated webrev.
>>>> 
>>>> Roland.
>>>> 
>>>>> 
>>>>> Thanks,
>>>>> Kris (OpenJDK username: krismo)
>>>>> 
>>>>> On Wed, Sep 30, 2015 at 1:34 AM, Roland Westrelin <roland.westrelin at oracle.com> wrote:
>>>>> I’m picking that one up. Here is a new webrev:
>>>>> 
>>>>> http://cr.openjdk.java.net/~roland/8003585/webrev.00/
>>>>> 
>>>>> The only change to c2 compared to the previous webrev is that ((x & m) u< m+1) is optimized the same way ((x & m) u<= m) is. Actually, I don’t think that C2 currently produces the ((x & m) u<= m) shape. The IfNode::fold_compares() logic produces the ((x & m) u< m+1) variant. I also added a test case to check the validity of the transformations and ran usual testing on the change.
>>>>> 
>>>>> Roland.
>>> 
>>