[13] RFR (S): 8161334: C2: Cast nodes hinder memory alias analysis

[Vladimir Ivanov]

Thanks, Tobias.

> the comment in memnode.cpp:1056 references 'B' which is not defined.

Added the following clarification:

-        //  L =  LoadQ(AddP(Check/CastPP(B), #Off))
-        //  S = StoreQ(AddP(             B , #Off), V)
+        //   B = << base >>
+        //   L =  LoadQ(AddP(Check/CastPP(B), #Off))
+        //   S = StoreQ(AddP(             B , #Off), V)

Best regards,
Vladimir Ivanov

> Otherwise, this looks good to me.
> 
> Best regards,
> Tobias
> 
> On 12.02.19 23:32, Vladimir Ivanov wrote:
>> http://cr.openjdk.java.net/~vlivanov/8161334/webrev.00/
>> https://bugs.openjdk.java.net/browse/JDK-8161334
>>
>> The following IR is produced for the slow case reported in the bug:
>>
>>    B = CastPP (DecodeN ...)                   // ...$C:NotNull
>>    S = StoreI M (AddP (            B) #off) V // ...$C:NotNull
>>    L = LoadI  S (AddP (CheckCastPP B) #off)   // ...$C:NotNull:exact
>>
>> MemNode::can_see_stored_value() can't prove S & L access the same location since AddPs are different
>> (since base nodes differ). There's a special case there, but only when Allocate is a base.
>>
>> Proposed patch generalizes existing Allocate case to the case when both base & offset are known to
>> be the same.
>>
>> Testing: hs-precheckin-comp, tier1-5
>>
>> Best regards,
>> Vladimir Ivanov