Unsafe for array access

[Andrew Haley]

On 05/07/2014 05:15 PM, Vladimir Kozlov wrote:
> Note, we do convert some user's bound check to array's range check. The example is Integer::valueOf():
> 
>      public static Integer valueOf(int i) {
>          if (i >= IntegerCache.low && i <= IntegerCache.high)
>              return IntegerCache.cache[i + (-IntegerCache.low)];
>          return new Integer(i);
>      }
> 
> The check is converted to ((i-IntegerCache.low) u< IntegerCache.length)

Did you mean

((i-IntegerCache.low) u< IntegerCache.high)

?


 and removed as duplicate of the generated range
> check for the following load.
> 
> length = (high - low) + 1
> 
> Vladimir
> 
> On 5/7/14 8:56 AM, John Rose wrote:
>>> On May 7, 2014, at 4:30 AM, Doug Lea <dl at cs.oswego.edu> wrote:
>>
>>>
>>> Relatedly, it might be be nice to have an intrinsic boundsCheck(array, index)
>>> that could be used in such cases that implemented using the more efficient
>>> (using C): (unsigned)index >= (unsigned)array.length, plus relied on more
>>> efficient VM throw mechanics on failure.
>>
>> We need an intrinsic like this for Arrays 2.0. Might as well do it now, since we have an immediate application.
>>
>> Counterpoint:  optimizer can and should generate similar code for plain user written range tests.
>>
>> Advice:  Do both, and the intrinsic will give everybody a clearer target to aim for. Unit test the intrinsic optimization, and several similar formulations.
>>
>> – John
>>