This is a complete duplicate of issue #56480 but for riscv-64.

Clang's intrinsics headers on Riscv-64 contain code like:

% head -20 /usr/lib/llvm-14/lib/clang/14.0.6/include/riscv_vector.h | tail -5

#ifndef __riscv_vector
#error "Vector intrinsics require the vector extension."
#endif

This means that one can only use Riscv-64 intrinsics in TUs that mark the feature as available for the entire intrinsic, e.g. via -march flags. In contrast, the x86 intrinsics are consistently defined, but tagged with __attribute__((__target__("whatever"))):

• https://github.com/llvm/llvm-project/blob/main/clang/lib/Headers/avx2intrin.h#L18

See also:

• https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=ae5e29239e28818f807cf11775c95c4243d9a256;hp=b8c7c62b2dbbdf355adb56d8250e68222ae0febb