RFR: 8305895: Implement JEP 450: Compact Object Headers (Experimental) [v26]

[Roberto Castañeda Lozano]

On Wed, 9 Oct 2024 16:21:53 GMT, Sandhya Viswanathan <sviswanathan at openjdk.org> wrote:

>> That seems to work, thanks @rkennke!
>> 
>> Since the [indexOf changes](https://github.com/openjdk/jdk/pull/20677/files#diff-ae1139bb5342494f9761e04389b090c543391bfdd7817af1625e854357c96e63) are complex and affect the default JVM configuration, they should be subject to the same level of scrutiny as if they were a standalone RFE, i.e. approved by at least a second reviewer. @sviswa7 could someone else at Intel have a second look and explicitly approve them?
>
> Yes, @vpaprotsk could review the changes that we made in src/hotspot/cpu/x86/c2_stubGenerator_x86_64_string.cpp.

Yes, that would be great. In the meantime, I ran a few thousand times the randomized test `java/lang/StringBuffer/ECoreIndexOf.java` with and without compact object headers, on product and debug builds, on different x64 implementations, and found no failures.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20677#discussion_r1793917912