RFR: JDK-8277382 make c1 BlockMerger use IR::verify only when necessary [v2]

[Nils Eliasson]

On Wed, 24 Nov 2021 12:52:32 GMT, Ludvig Janiuk <duke at openjdk.java.net> wrote:

>> This PR removes two calls to `IR::verify` which were unnecessary. The reason they are unnecessary is that `try_merge` does not always take any action. There is not need to verify if nothing has changed. In the cases that `try_merge` does do anything, it already calls `IR::verify` afterwards.
>> 
>> This PR also switches some deeply nested if statements in `try_merge` to early returns.
>
> Ludvig Janiuk has updated the pull request incrementally with one additional commit since the last revision:
> 
>   indentation error fixed

Looks good!

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Marked as reviewed by neliasso (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/6456