RFR: 8325169: Reduce String::indexOf overheads

[ExE Boss]

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

src/java.base/share/classes/java/lang/String.java line 2506:

> 2504:         fromIndex = Math.max(0, fromIndex);
> 2505:         return isLatin1() ? StringLatin1.indexOf(value, ch, fromIndex, value.length)
> 2506:                 : StringUTF16.indexOf(value, ch, fromIndex, value.length >> 1);

This needs to include the check for `fromIndex >= this.length()`:
Suggestion:

        fromIndex = Math.max(0, fromIndex);
        int toIndex = length();
        if (fromIndex >= toIndex) {
            return -1;
        }
        return isLatin1()
                ? StringLatin1.indexOf(value, ch, fromIndex, toIndex)
                : StringUTF16.indexOf(value, ch, fromIndex, toIndex);

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PR Review Comment: https://git.openjdk.org/jdk/pull/17685#discussion_r1476268336