As a compiler guy, the complaint about "opaque templates and function calls" to me raises serious doubts that the author has any idea what they're talking about

As a compiler guy, the complaint about "opaque templates and function calls" to me raises serious doubts that the author has any idea what they're talking about. std::simd is designed to be akin to taking vector operations as intrinsics on <4 x f32> and similar types and wrapping them in a more C++ dialect than bare compiler intrinsics (and then a second layer on top of that to make things somewhat more portable). So the implementation of all of the std::simd at the bottom should be tiny functions that map to essentially a single instruction, specified via a header file in a mechanism that guarantees you always have the body. This makes the functions trivially obvious candidates for inlining. Since it's a C++26 addition, the dispatching logic through the layers can largely be done via if constexpr, which means most of the code is discarded by the frontend. Given that the complaint seems to be about not vectorizing a call to a sin function, it's possible that it's implemented in libstdc++ in such a way that the library doesn't know about the compiler's -fveclib implementation. But then again, the complaint is based on the libstdc++ v14 implementation of C++ Parallelism std::simd, not the v16.1 implementation of C++26 std::simd, which is completely different (and landed circa 2 months ago).