RFR: 8221723: Avoid storing zero to String.hash

[Aleksey Shipilev]

On 4/1/19 1:57 PM, Claes Redestad wrote:
> when a String has a calculated hash code value of 0, we recalculate and
> store a 0 to the String.hash field every time (except for the empty
> String, which is special cased). To make String objects more amenable to
> storage in shared read-only memory, e.g., CDS archives, we should avoid
> this redundant store.
> 
> Bug:    https://bugs.openjdk.java.net/browse/JDK-8221723
> Webrev: http://cr.openjdk.java.net/~redestad/8221723/

Looks fine. I recall we were fixing something like this, but I might be confusing it with the other
RFE [0]. The comment might emphasize we are doing it for RO memory:

   // Avoid issuing a store if the calculated value is also zero:
   // in addition to minor optimization benefit, this also allows storing
   // Strings with zero hash code in read-only memory.

-Aleksey

[0] https://bugs.openjdk.java.net/browse/JDK-6921374