RISC-V: allow building scalable RVV support with GCC, LLVM 16 support

[mshabunin]

Related issue #22608

• GCC does not support "overloaded RVV intrinsics", but we can add some of them in our code
• LLVM since version 16 uses __riscv_<name> naming scheme (see related ticket), so we need to add compatibility headers to rename our 0.10 intinsics to the new scheme (also for some "overloaded intrinsics")

TODO:

• check and fix compilation with GCC still does not work due to toolchain issue or limitation
• extract overloaded intsinsics implementation to separate header
• macros for overloaded intrinsics looks too broad, maybe convert them to function macros / inline functions / undef? used headers from RISC-V collab as is
• clean-up the code - reduce modifications

Note: scalable RVV compilation using GCC still does not work (T-Head 2.6.1 and RISC-V Collab Toolchain@rvv_next) due to compiler issues or limitations. More analysis needed.

force_builders=Custom
build_image:Custom=riscv-clang-rvv
Xbuild_image:Custom=riscv-clang-rvv-128
Xbuild_image:Custom=riscv-gcc-rvv-07
test_modules:Custom=core,imgproc,dnn
buildworker:Custom=linux-4
test_timeout:Custom=600
build_contrib:Custom=OFF

[opencv-alalek]

LGTM 👍

[zhongjuzhe]

Can you use upstream GCC (GCC 13.0) test? We don't maintain rvv-next any more. All update upstream GCC directely.
https://github.com/gcc-mirror/gcc

[opencv-alalek]

@zhongjuzhe Thank you for the information!
Is there some example how to build RISC-V GCC toolchain from upstream source code? (similar to https://github.com/riscv-collab/riscv-gnu-toolchain instructions)
CI logs? Or Dockerfile?

[zhongjuzhe]

It seems that RISC-V toolchain doesn't bump to latest upstream GCC. I think you can file an issue to @kito-cheng and ask him to update the toolchain.

Here is an simple example to verify that both GCC and LLVM are consisten each other with the same API doc:
https://godbolt.org/z/dz83ozbeb

compiler explorer has showed that both GCC and LLVM are recognizing same API RVV.

[mshabunin]

I've been able to build riscv-collab toolchain with the latest GCC by updating gcc submodule to master manually. It can build OpenCV with scalable RVV support, but failed to build non-scalable (intrin_rvv.hpp) variant. I'm going to take a closer look. @zhongjuzhe , thank you for guidance!

[zhongjuzhe]

Thank you for trying. Feel free file a bug here: https://gcc.gnu.org/bugzilla/ if you see any compiler bug. Thanks. ***@***.*** From: Maksim Shabunin Date: 2023-04-17 18:21 To: opencv/opencv CC: Ju-Zhe Zhong; Mention Subject: Re: [opencv/opencv] RISC-V: allow building scalable RVV support with GCC, LLVM 16 support (PR #23383) I've been able to build riscv-collab toolchain with the latest GCC by updating gcc submodule to master manually. It can build OpenCV with scalable RVV support, but failed to build non-scalable (intrin_rvv.hpp) variant. I'm going to take a closer look. @zhongjuzhe , thank you for guidance! — Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you were mentioned.Message ID: ***@***.***>