RFR: 8318457: Use prefix-less prepend methods directly to reduce branches in String concat expressions [v3]

[Claes Redestad]

On Thu, 19 Oct 2023 15:59:54 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> In #16006 using `StringConcatFactory` seem to induce a run-to-run variance. One idea to reduce this is to generate expression trees with fewer branches by looking up and using the prefix-less `prepend` methods directly for cases where constant is null/empty so that the prefixed prepender will always deal with a non-null prefix constant.
>
> Claes Redestad has updated the pull request incrementally with one additional commit since the last revision:
> 
>   drop dropLookupMode

Using dropLookupMode caused a bootstrap cycle in tests where a SecurityManager is installed, causing lots of test failures. Reverting that part.

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PR Comment: https://git.openjdk.org/jdk/pull/16244#issuecomment-1771296318