RFR: 8320448: Accelerate IndexOf using AVX2 [v43]

[Scott Gibbons]

On Tue, 28 May 2024 20:29:38 GMT, Sandhya Viswanathan <sviswanathan at openjdk.org> wrote:

>> No.  This is checking for a zero length haystack.  The following compare checks for needle length longer than haystack, regardless of the value in each.  The comparison is signed, so a haystack length of 0 with a needle length of -1 will pass the following test and assume validity.
>
> But we have already checked for needle length to be greater than 0 in the following lines:
> __ cmpq(needle_len_p, 0);
>  __ jg_b(L_nextCheck);

OK

>> Again, I think we ought to leave this in.  Although it executes ~3 instructions that may not be necessary in some cases I think it's best to perform the check.  Once we have a good enough test to check reading past the end of the haystack we can change it.
>
> In this particular case, we are returning -1 (NoMatch), so no need to do L_checkRangeAndReturn here, we could directly jump to L_returnError.

OK.

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PR Review Comment: https://git.openjdk.org/jdk/pull/16753#discussion_r1617876757
PR Review Comment: https://git.openjdk.org/jdk/pull/16753#discussion_r1617874637