Arm Posts GCC Tuning Patches For Neoverse-N2 & New Neoverse-Demeter

Arm continues working on improving the open-source compiler support for their forthcoming Armv9 processor designs. The latest to report on is the tuning additions for the Neoverse-N2 and Neoverse "Demeter" targets.

Going back to late 2020 Arm engineers began working on Neoverse-N2 support for the GNU toolchain and for the LLVM/Clang compiler too. Now they have posted the actual tuning information for the Neoverse-N2 that has the calculated costs for different operations so the compiler can make more informed choices for these forthcoming processors.

This patch has those cost tables that are accurate for the new Arm CPU design. Up to now GCC was relying upon the generic and Arm Cortex-A57 costs for the N2.

Another patch sent out today adds Arm tuning for the Neoverse-Demeter. This also adds in the -mcpu=demeter and -mtune=demeter options. GCC up to now did not have the Arm Demeter target. Demeter is Armv9-A and enables I8MM, BF16, BITPERM, RNG, MEMTAG (MTE), and PROFILE features on top of the standard AArch64 capabilities.

There hasn't been much (any?) public talk of the Arm Neoverse Demeter besides acknowledging it in some code comments pertaining to Coreboot and other system firmware around the "Demeter" CPU.

Right now these Arm tuning patches are on the mailing list while we'll see soon if they try to squeeze them still into the GCC 12 release that is expected to come out around April.