RFR: 8232165: Reduce allocations in ValueStack copying constructor

[Nils Eliasson]

Hi Claes,

Looks good.

// Nils

On 2019-10-11 13:42, Claes Redestad wrote:
> Hi,
>
> this patch optimizes C1 ValueStack copying, which reduces unnecessary
> allocations and has a small but measurable impact on compilation speed.
>
> Webrev: http://cr.openjdk.java.net/~redestad/8232165/open.00/
> Bug:    https://bugs.openjdk.java.net/browse/JDK-8232165
>
> Testing: tier1-2 (tier3-4 ongoing)
>
> Thanks!
>
> /Claes