Just as the title says, it's OpenJDK with microarch specified and -O3. Linux only. These are not tested for conformance to any Java specification, but they do work with Minecraft 1.12.2. Compiler optimisations may or may not result in broken Java functions; if this does happen, please let me know at amoore@ashleighhost.net! These are built from the official OpenJDK source code.
I made this because I got bored and after a straight week of hell getting GCC 12 and Java 8's code to play nice (thanks Gentoo for having a bug report for the exact same issue on their backend), discovered that I had at least a four times performance increase in a particularly heavily modded Minecraft instance, going from an min of 15 and a max of 35 FPS to a min of 25 and a max of 60 FPS with headroom to spare. Memory bandwidth bottlenecks were also helped by this by an unknown amount. I surmise any Java application with heavy memory or I/O operations will see a performance uplift by using these binaries. Right now, it's only Java 8; 17 and 21 may come in the future.
They can be acquired here. Make sure you pick the right one for your CPU, or else it will crash with an "Illegal Instruction" error.