google
Failure to compile with clang++ 20 on riscv64
$ clang++ -c -stdlib=libc++ -I. hwy/per_target.cc In file included from hwy/per_target.cc:28: In file included from ./hwy/highway.h:629: ./hwy/ops/rvv-inl.h:644:17: error: use of undeclared identifier '__riscv_vsetvlmax_e8mf8' 644 | HWY_RVV_FOREACH(HWY_RVV_LANES, Lanes, setvlmax_e, _ALL) | ^ ./hwy/ops/rvv-inl.h:644:17: error: use of undeclared identifier '__riscv_vsetvl_e8mf8' ./hwy/ops/rvv-inl.h:644:17: error: use of undeclared identifier '__riscv_vsetvl_e8mf8' ./hwy/ops/rvv-inl.h:644:17: error: use of undeclared identifier '__riscv_vsetvlmax_e16mf4' ./hwy/ops/rvv-inl.h:644:17: error: use of undeclared identifier '__riscv_vsetvl_e16mf4' ./hwy/ops/rvv-inl.h:644:17: error: use of undeclared identifier '__riscv_vsetvl_e16mf4' ./hwy/ops/rvv-inl.h:644:17: error: use of undeclared identifier '__riscv_vsetvlmax_e32mf2' ./hwy/ops/rvv-inl.h:644:17: error: use of undeclared identifier '__riscv_vsetvl_e32mf2' ./hwy/ops/rvv-inl.h:644:17: error: use of undeclared identifier '__riscv_vsetvl_e32mf2' ./hwy/ops/rvv-inl.h:644:17: error: use of undeclared identifier '__riscv_vsetvlmax_e64m1' ./hwy/ops/rvv-inl.h:644:17: error: use of undeclared identifier '__riscv_vsetvl_e64m1' ./hwy/ops/rvv-inl.h:644:17: error: use of undeclared identifier '__riscv_vsetvl_e64m1' ./hwy/ops/rvv-inl.h:644:17: error: use of undeclared identifier '__riscv_vsetvlmax_e64m2' ./hwy/ops/rvv-inl.h:644:17: error: use of undeclared identifier '__riscv_vsetvl_e64m2' ./hwy/ops/rvv-inl.h:644:17: error: use of undeclared identifier '__riscv_vsetvl_e64m2' ./hwy/ops/rvv-inl.h:644:17: error: use of undeclared identifier '__riscv_vsetvlmax_e64m4' ./hwy/ops/rvv-inl.h:644:17: error: use of undeclared identifier '__riscv_vsetvl_e64m4' ./hwy/ops/rvv-inl.h:644:17: error: use of undeclared identifier '__riscv_vsetvl_e64m4' ./hwy/ops/rvv-inl.h:644:17: error: use of undeclared identifier '__riscv_vsetvlmax_e64m8' fatal error: too many errors emitted, stopping now [-ferror-limit=] 20 errors generated.
Hi, due to https://github.com/llvm/llvm-project/issues/56592 clang currently still requires a flag like -march=rv64gcv1p0. HTH?
The difference is that clang 20 started advertising support for __riscv_v_intrinsic, without which we do not attempt to use RVV.
For reference, commit 6bd4bdded4fe666dc90872fd4472b967b6e5cd55 implies that Clang 20.1.x is now required when compiling for RISC-V, see: https://github.com/llvm/llvm-project/commit/05b3d26181ade32f5988d2be4939f605a5225782
Right. Unfortunately Clang had a breaking change with VXRM for which there was no feature test. Requiring 1.0 'fails safe' in that regard. You can override this by defining HWY_BASELINE_TARGETS directly.
@andreas-schwab and @jan-wassenberg, the issue was that Clang 20 and later on RISC-V define __riscv_v_intrinsic, even when the "V" extension is not enabled. I have implemented a fix in pull request #2586 that fixes this issue that checks that __riscv_v is also defined.
That's how it is supposed to be, see the RISC-V Vector C Intrinsic Specification:
Chapter 2. Test macro The __riscv_v_intrinsic macro is the C macro to test the compiler’s support for the RISC-V "V" extension intrinsics. This macro should be defined even if the vector extension is not enabled.
That's how it is supposed to be, see the RISC-V Vector C Intrinsic Specification:
Chapter 2. Test macro The __riscv_v_intrinsic macro is the C macro to test the compiler’s support for the RISC-V "V" extension intrinsics. This macro should be defined even if the vector extension is not enabled.
@andreas-schwab Thanks for pointing this out.
I have also made some additional changes to rvv_ops-inl.h and set_macros-inl.h in pull request #2587 that along with the changes in pull request #2586 allow Google Highway to be compiled for RISC-V with dynamic dispatch enabled with Clang 20 or later.
I have also made some additional changes to rvv_ops-inl.h and set_macros-inl.h in pull request #2587 that along with the changes in pull request #2586 allow Google Highway to be compiled for RISC-V with dynamic dispatch enabled with Clang 20 or later.
Could the RVV runtime dispatch check be fixed then? It is currently still disabled by && 0: https://github.com/google/highway/blob/master/hwy/detect_targets.h#L752
hm, if it's just a matter of removing the && 0 sure, but when I also remove gcv from the build flags, there are build failures with float16 sseg2 when building interleaved_test.