RFR(S): fix System.arraycopy() C2 intrinsics with arrays of value types

[Tobias Hartmann]

Hi Roland,

On 27.11.2017 14:08, Roland Westrelin wrote:
> copy_type is set to dest_elem and is returned from the method so it's
> not that simple, right?

Right, my bad.

> I hit that problem when running the new tests with -Xcomp. In the
> address computation of:
> 
> src[i-1]
> 
> the constant part is negative (header size + (-1) * field offset).

Okay, makes sense.

> I think the problem was: 
> 
> when converting an arraycopy to a series of loads/stores, the memory
> state is a MergeMem mm,
> 
> first load a value, without the change, memory edge is mm
> 
> store the value, memory state is one of the input of mm, mm is updated
> to point to the store
> 
> and we have a cycle:
> 
> ST->LD->MM-\
> ^----------/

Thanks for the explanation! Maybe rename "m" to "load_mem" or something more informative.

No need to send another webrev assuming that you've executed the relevant hotspot tests.

Best regards,
Tobias