RFR: 8259020: null-check of g1 write_ref_field_pre_entry is not necessary

[Albert Mingkun Yang]

On Thu, 31 Dec 2020 08:12:46 GMT, Xin Liu <xliu at openjdk.org> wrote:

> orig is not null because G1BarrierSetC2 won't invoke write_ref_field_pre_entry 
> if pre_val is NULL.

Marked as reviewed by ayang (Author).

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PR: https://git.openjdk.java.net/jdk/pull/1913