LLVM Plumbs Support For Intel Golden Cove's New SERIALIZE Instruction
Written by Michael Larabel in LLVM on 2 April 2020 at 07:07 AM EDT. 1 Comment
Yesterday we noted Intel's programming reference manual being updated with new Golden Cove instructions for Sapphire Rapids and Alder Lake and with that Intel's open-source developers have begun pushing their changes to the compilers. The latest updates add TSXLDTRK, a new HYBRID bit for Core+Atom hybrid CPUs, and a new SERIALIZE instruction. After GCC was receiving the patch attention yesterday, LLVM is getting its attention today.

Being merged today to LLVM 11 is support for Intel's new SERIALIZE instruction for those 2021 processors.

As outlined yesterday, the SERIALIZE instruction for Alder Lake and Sapphire Rapids will serialize the instruction execution. SERIALIZE will make sure that all modifications to flags / registers / memory by previous instructions are complete and all buffered writes are pushed to memory.

LLVM now has support for SERIALIZE and for now is just enabled with the -mserialize flag but not enabled for any CPU target yet. The performance impact of SERIALIZE is likely to be quite significant while we await to see Intel's future guidance about their recommended usage of SERIALIZE over existing serializing instructions.

Also ready to land for LLVM is TSXLDTRK instructions as another one of the newly-published additions for Golden Cove. TSXLDTRK is Intel TSX Suspend Load Address Tracking.

LLVM/Clang 11.0 should be out in September~October and will likely have good Sapphire Rapids / Alder Lake CPU support in place well ahead of their anticipated launches in 2021.
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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 20,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.

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