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Toolchain

README.md

Toolchain

In order to build muRISCV-NN you can either use the RISC-V GCC or upstream LLVM. However, if you want to use the supported RISC-V extensions (V or P) in order to accelerate your code you will need to pay special attention to which version of each toolchain you are using.

  • If you just want to compile the scalar code without any hardware acceleration you will need a rv32gc compiler.
  • If you want to use the V vector accelerated kernels by activating USE_VEXT you will need a rv32gcv compiler.
  • If you want to use the P packed accelerated kernels by activating USE_PEXT you will need a rv32gcp compiler.

GCC

GCC has support for both the V vector and the P packed extensions. The easiest way to acquire a GCC toolchain is through the download.sh script in the /Toolchain directory. This will download precompiled GCC toolchains we provide for you. The downdload_lite.sh will download a bare minimum version intended for use with LLVM and can thus not be used as a standalone GCC toolchain.

Once you have your GCC toolchain setup, don't forget to supply the -march=rv32gcv/-march=rv32gcp and -mabi=ilp32d flags when compiling with special instructions. However, no need to worry about this if you don't change anything. CMake takes care of that for you.

LLVM

Upstream LLVM 14 now has full support for RISC-V and even the RISC-V vector extension. However, it does not yet support the P packed extension.

You can install LLVM 14 from here and follow the instructions under "Automatic installation script". LLVM still requires you to have a RISC-V GCC toolchain, as LLVM does not provide its own headers and libraries.

Currently, we have to force Clang to use the lld linker, as it otherwise wants to use the x86 native linker (which obviously won't work). I tried using the GCC linker, but LLVM hands it a weird march argument that it doesn't understand -march=rv32i2p0_m2p0_a2p0_f2p0_d2p0_c2p0_v0p10_zvlsseg0p10: unsupported ISA subset z.

Once you have everything setup you will need to invoke Clang with the following arguments:
--target=riscv32 -march=rv32gcv0p10 -mabi=ilp32d -menable-experimental-extensions --sysroot=<path-to-gcc-toolchain>/rv32gcv/riscv32-unknown-elf --gcc-toolchain=<path-to-gcc-toolchain>/rv32gcv -fuse-ld=lld-14

LLVM 13 also has RISC-V and RISC-V vector support. However, it is only experimental in that version (use LLVM 14 instead if you can!). You need to add -menable-experimental-extensions and -mno-relax when compiling with LLVM 13. For more info, look here and here.

Compile your own GCC

Scalar rv32gc

Simply follow the instructions listed in the README.md in the GCC GitHub repo and build your toolchain from the main branch. You can also find GCC binaries through companies like SiFive or Imperas, or even through some package managers.

Vector rv32gcv or rv32imv

GCC's RISC-V vector support used to be quite bad. However, thanks to efforts from RISC-V collaborators GCC now supports the latest RISC-V vector 1.0 spec, as well as intrinsics (and autovectorization, but this feature seems to not perform very well yet).

Steps

  • git clone [email protected]:riscv-collab/riscv-gnu-toolchain.git and git checkout rvv-next
  • export PATH=$PATH:/opt/riscv/bin (ensure that your have rwx to /opt)
  • ./configure --prefix=/opt/riscv --with-arch=rv32gcv --with-abi=ilp32d
  • make

This will take a while and build a rv32gcv into /opt/riscv.

In order to build rv32imv simply replace the configure command with

  • ./configure --prefix=/opt/riscv --with-arch=rv32imv --with-abi=ilp32

Packed rv32gcp

GCC's itself does not yet offer P packed support. However, there are two PRs open for that. See here GCC and here binutils.

Steps

[submodule "riscv-binutils"]
  path = riscv-binutils
  url = https://github.com/linsinan1995/riscv-binutils-gdb.git
  branch = riscv-binutils-experiment-p-ext
[submodule "riscv-gcc"]
  path = riscv-gcc
  url = https://github.com/linsinan1995/riscv-gcc.git
  branch = riscv-gcc-experiment-p-ext

Make sure the two directories now contain the latest commit of the respective PRs.

  • export PATH=$PATH:/opt/riscv/bin (ensure that you have rwx rights to /opt)
  • ./configure --prefix=/opt/riscv --with-arch=rv32gcp --with-abi=ilp32d
  • make

This will take a while and build a rv32gcp into /opt/riscv.