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

[Tobias Hartmann]

Hi Vladimir,

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

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