LLVM Clang 12 Merges Support For x86_64 Microarchitecture Levels
Written by Michael Larabel in LLVM on 22 October 2020 at 09:02 AM EDT. 10 Comments
LLVM --
In an effort to better cater towards newer and common x86_64 instruction set extensions, open-source toolchain developers are moving ahead with the work on x86_64 micro-architecture feature levels for being able to target a handful of different "levels" beyond the base x86_64 instruction set.

The x86_64 feature levels are for easily segregating different classes of x86_64 Intel/AMD CPUs in hopes of making it easier for Linux distributions to increase their base requirements beyond just x86_64/AMD64 and improving compiler toolchains with a common set of possible levels / hardware capabilities in generating optimized libraries. This goes along with work pursued by Red Hat in raising the x86_64 CPU requirements for new RHEL/Fedora releases and for optimization initiatives like the glibc HWCAPS in supporting a few different optimization levels rather than having to target every possible Intel/AMD CPU microarchitecture family as is currently done for code optimization/tuning.

This past week LLVM Clang 12 added support for feeding the x86_64 feature levels into the Clang C/C++ compiler.

The defined x86_64 feature levels include:
x86-64: CMOV, CMPXCHG8B, FPU, FXSR, MMX, FXSR, SCE, SSE, SSE2
x86-64-v2: (close to Nehalem) CMPXCHG16B, LAHF-SAHF, POPCNT, SSE3, SSE4.1, SSE4.2, SSSE3
x86-64-v3: (close to Haswell) AVX, AVX2, BMI1, BMI2, F16C, FMA, LZCNT, MOVBE, XSAVE
x86-64-v4: AVX512F, AVX512BW, AVX512CD, AVX512DQ, AVX512VL

The different levels/versions can be fed now into -march= for Clang 12 and GCC 11 if wanting to optimize for one of those targets rather than specifying specific instruction set extensions manually or a CPU family.

These baselines are laid out via the
Related News
About The Author
Author picture

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.

Popular News This Week