RFR: 8325169: Reduce String::indexOf overheads

[Roger Riggs]

On Fri, 2 Feb 2024 13:54:46 GMT, Claes Redestad <redestad at openjdk.org> wrote:

> This patch streamlines and specializes various `String::indexOf` methods. Mainly avoids the need for clamping and doing checks that are redundant in almost all cases, moving the checks to the API boundary where they are needed. 
> 
> This improves performance both at peak and during startup/warmup. Since indexOf is heavily used in bootstrapping code it makes sense to slightly dial back abstraction and delegation, which in this case also brought some benefit to peak performance.
> 
> Testing: tier1-3

Looks ok as a performance improvement; some comments about assertions might be useful for future readers.

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Marked as reviewed by rriggs (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/17685#pullrequestreview-1860173585