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

Vladimir Ivanov vladimir.x.ivanov at oracle.com
Thu May 19 20:29:59 UTC 2016

Thanks for the feedback, Vladimir.

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

Fixed. Updated webrev.9.00 in place.

> Why CastIINode::cmp() returns uint?

That's how Node::cmp() is declared:

   virtual uint cmp( const Node &n ) const;

Best regards,
Vladimir Ivanov

> 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

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