[8u/9] RFR (S): 8154831: CastII/ConvI2L for a range check is prematurely eliminated

[Vladimir Kozlov]

Can you make subnode.cpp changes in jdk9 and 8u similar?

Why CastIINode::cmp() returns uint?

Thanks,
Vladimir

On 5/19/16 10:45 AM, Vladimir Ivanov wrote:
> http://cr.openjdk.java.net/~vlivanov/8154831/webrev.9.00/
> http://cr.openjdk.java.net/~vlivanov/8154831/webrev.8u.00/
> https://bugs.openjdk.java.net/browse/JDK-8154831
>
> CastII node prematurely goes away and causes a cascade of other
> eliminations which severely corrupts the graph (the actual crash happens
> due to a memory edge coming from a non-dominating region).
>
> CastII is replaced with TOP due to a type conflict (ranges don't
> intersect) between the actual type of the value being range checked and
> the type CastII tries to assign.
>
> It happens on effectively dead path (range check always fails) which C2
> can't eliminate due to a missing transformation for CmpU:
>
>    Bool [lt] (CmpU (ConI #-1) (… #int)) => (ConI #0)
>
> The fix is to add the missing case in CmpUNode::sub(). It enables dead
> path elimination along with CastII.
>
> Also, fixed a couple of missing cases in 8u (not applicable in 9):
>   * CastII nodes shouldn't be eliminated during CCP pass;
>   * CastII comparion should take _range_check_dependency flag into account.
>
> Testing:
>   * JPRT (8u/9);
>   * RBT for 9 (hs-tier0-comp - in progress);
>   * replay of problematic compilation (8u).
>
> Thanks!
>
> Best regards,
> Vladimir Ivanov