RFR: 8272377: assert preconditions that are ensured when created in add_final_edges [v2]

[Vladimir Kozlov]

On Thu, 19 Aug 2021 07:03:50 GMT, Yi Yang <yyang at openjdk.org> wrote:

>> I think we can assert preconditions, which are ensured by add_node_to_connection_graph when they were first added to CG, in add_final_edges when they are delay handled, then we can skip checking these preconditions in runtime(assertions instead). This PR also does some code refactor.
>
> Yi Yang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   use Unexpected node type message

I am fine with refactoring: using `switch()` and passing `mergemem_worklist` as argument.

Using `ELSE_FAIL()` macro was very helpful during development and I kept it.
But we did not see such failure for long time so I am fine with replacing it with just assert.

Testing ran by Tobias was clean.

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Marked as reviewed by kvn (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/5101