RFR(XS): 8216549: Mismatched unsafe access to non escaping object fails

[Vladimir Ivanov]

Looks good.

Best regards,
Vladimir Ivanov

On 11/01/2019 01:16, Roland Westrelin wrote:
> 
> http://cr.openjdk.java.net/~roland/8216549/webrev.00/
> 
> test1(), test2() and test3() perform an unsafe access with a mismatched
> access.
> 
> test1() compiles to an unschedulable graph and causes the compiler to
> crash. The memory input of the load from a non escaping allocation
> initially points to a membar but is set to bypass the membar while
> control stays set to the membar. The load is not eliminated because it's
> a mismatched memory access, an anti dependence is added between the
> membar and the load and the graph is unschedulable.
> 
> test2() and test3() return wrong results: the access is mismatched and
> misaligned, it's given its own alias by c2 but the MergeMem right after
> the allocation only points to the allocation for actual fields of the
> newly allocated object. So the load memory input is set to the memory
> state on method entry and the load is optimized as zero.
> 
> I simply propose to make non escaping allocations with mismatched
> accesses to be non scalar replaceable.
> 
> Roland.
>