RFR(S): 8215265: C2: range check elimination may allow illegal out of bound access

[Vladimir Kozlov]

On 12/19/18 7:35 AM, Roland Westrelin wrote:
> 
> Hi Vladimir,
> 
> Thanks for looking at this.
> 
>> pre_limit = (low_limit - offset - (scale_con - 1)) / scale_con
> 
> pre_limit = (low_limit - offset + (scale_con - 1)) / scale_con
> 
> to round up?

Yes, my bad.

> 
> But then there's a risk of overlow of low_limit - offset + (scale_con -
> 1).
> 
> So it would need to be:
> 
> l = (low_limit - offset) / scale_con
> pre_limit = l + ((low_limit - offset - l * scale_con) != 0 ? 1 : 0)
> 
> That's why I went with always +1 if scale > 1.

Okay. I was thinking about more complex solution since we can come up with some expressions to check overflow and 
convert it into max_int (which will lead to use loop_limit). But on other hand this code is rarely (never) executed when 
Loop Predicates are used (which is default). I agree for your solution.

Thanks,
Vladimir

> 
> Roland.
>