RFR: Fix verification of remembered set at mark start [v2]

[William Kemper]

On Wed, 11 Jan 2023 01:39:28 GMT, Kelvin Nilsen <kdnilsen at openjdk.org> wrote:

>> All objects residing between TAMS and top() within each old region are examined independent of the marking context.
>
> Kelvin Nilsen has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Simplify rem-set verification code at init mark
>    
>    The code as originally written was mostly correct.  Use that
>    implementation with just a few refinements to properly handle promotions
>    that occur during concurrent old-gen marking.
>  - Simplify the fix to rem-set verifier
>    
>    Just remove the offending assert().  The code as originally written
>    should work ok.

Marked as reviewed by wkemper (Committer).

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PR: https://git.openjdk.org/shenandoah/pull/197