3.2.1. About LLVM Toolchain

The current llvm toolchain is developed based on the upstream V19.1.7, for extensions we supported, check below:

You can find our llvm source code in https://github.com/riscv-mcu/llvm-project/tree/nuclei/19.x

Note

The LLVM toolchain is implemented based on the upstream version. Many features can be referenced in the official LLVM documentation: https://llvm.org/docs/. Please refer to the corresponding LLVM release version in the documentation for accurate details. Local documentation is also available under gcc/share/doc/llvm/docs/html within the toolchain directory.

3.2.2. Extensions Support

Ratified Extensions

  • Basic Extensions

    i, m, a, f, d, c, h(Assembly only), zaamo, zalrsc, zicsr, zifencei, zihintpause(Assembly only), zicond, zawrs(Assembly only), zfh, zfhmin, zmmul, svinval(Assembly only), svnapot(Assembly only), svpbmt.

  • Z*inx Extensions

    zfinx, zdinx, zhinx, zhinxmin.

  • CMO Extensions(Assembly only)

    zicboz, zicbom, zicbop.

  • Bitmanip Extensions

    zba, zbb, zbc, zbs

  • Crypto Extensions

    zbkb, zbkc, zbkx, zknd, zkne, zknh, zkr, zks, zksed, zksh, zkt.

  • Vector Extensions

    zve32x, zve32f, zve64x, zve64f, zve64d, zvfh, zvfhmin, v.

  • Zc Extensions

    zca, zcb, zce, zcf, zcd, zcmp(Assembly only), zcmt(Assembly only).

  • Zvb Extensions

    zvbb, zvbc

  • Zvk Extensions

    zvkg, zvkned, zvknha, zvknhb, zvksed, zvksh, zvkn, zvknc, zvkng, zvks, zvksc, zvksg, zvkt.

  • Zilsd Extensions

    Zilsd, Zclsd

  • Xxlcz Extensions(Assembly only)

    xxlczpstinc, xxlczbmrk, xxlczbitop, xxlczslet, xxlczabs, xxlczmac, xxlczbri, xxlczbitrev, xxlczgp.

  • Packed SIMD Extension 0.5.4(Assembly only)

    xxldsp, xxldspn1x, xxldspn2x, xxldspn3x.

    • xxldsp: P-spec-v0.54 + Nuclei Custom EXPD* instructions

    • xxldspn1x: xxldsp + Nuclei Custom N1

    • xxldspn2x: xxldsp + Nuclei Custom N1 & N2

    • xxldspn3x: xxldsp + Nuclei Custom N1 & N2 & N3

  • Nuclei custom VPU Extensions

    xxlvqmacc

Experimental Extensions

LLVM supports (to various degrees) a number of experimental extensions. All experimental extensions have experimental- as a prefix. Listed below:

smaia, ssaia, zacas, zfa, zfbfmin, zvfbfmin, zvfbfwma, zicond, zihintntl, ztso, zvbb, zvbc, zvkg, zvkn, zvknc, zvkned, zvkng, zvknha, zvknhb, zvks, zvksc, zvksed, zvksg, zvksh, zvkt, zilsd, zclsd.

Note

To use an experimental extension from clang, you must add -menable-experimental-extensions to the command line, and specify the exact version of the experimental extension you are using. To use an experimental extension with LLVM’s internal developer tools (e.g. llc, llvm-objdump, llvm-mc), you must prefix the extension name with experimental-.

3.2.3. General Options

-march=<cpu>

Specify that Clang should generate code for a specific processor family member and later. For example, if you specify -march=i486, the compiler is allowed to generate instructions that are valid on i486 and later processors, but which may not exist on earlier ones.

-mcmodel=<arg>

-mcmodel=medany (equivalent to -mcmodel=medium), -mcmodel=medlow (equivalent to -mcmodel=small)

-mcpu=help, -mtune=help

Print out a list of supported processors for the given target (specified through --target=<architecture> or -arch <architecture>). If no target is specified, the system default target will be used.

-fno-vectorize

Use -fno-vectorize and -fno-slp-vectorize to disable LLVM19 automatic vectorization for RVV; by default, automatic vectorization is enabled.

Optimization Option

-O0

Means “no optimization”: this level compiles the fastest and generates the most debuggable code.

-O/-O1

Somewhere between -O0 and -O2.

-O2

Moderate level of optimization which enables most optimizations.

-O3

Like -O2, except that it enables optimizations that take longer to perform or that may generate larger code (in an attempt to make the program run faster).

-Ofast

Enables all the optimizations from -O3 along with other aggressive optimizations that may violate strict compliance with language standards.

-Os

Like -O2 with extra optimizations to reduce code size.

For more about RISC-V options used by LLVM toolchain, please check https://releases.llvm.org/19.1.0/docs/RISCVUsage.html

3.2.4. Install and Setup

More information on building and running LLVM, see https://llvm.org/docs/GettingStarted.html#getting-the-source-code-and-building-llvm

3.2.5. Changelog

Please check Changelog here.

3.2.6. Checking LLVM Version

To check the basic version information of LLVM, you can use the command riscv64-unknown-elf-clang -v.

If you need to report an issue to the developers, please provide:

  1. The gcc/build.txt file (located in the GCC directory) for GCC compilation details.

  2. The gcc/gitrepo.txt file to confirm commit IDs of each tool, which helps determine more detailed build information.