That is, code using immintrin.h tends to fail to compile when using modules while working fine with headers.
I'll try to produce a minimal example in the next few hours.
For now, I have an example using boost_unordered.
When problems showed up in my own code using intrinsics, I could generally fix it by declaring all arguments as variables, and then passing the lvalues to the intriinsic function.

Hello.cxxm:

#ifndef USE_HEADERS module; #endif #include <boost/unordered/unordered_flat_map.hpp> #include <iostream> #ifndef USE_HEADERS export module Hello; export { #endif void hello() { std::cout << "Hello World!\n"; } template <typename K, typename V> using map = boost::unordered_flat_map<K, V>; #ifndef USE_HEADERS } #endif

user.cpp:

#ifndef USE_HEADERS import Hello; #else #include "hello.cxxm" #endif int main() { hello(); int x = 0; long y = 0; map<int*,long*> m; m[&x] = &y; [[maybe_unused]] auto f = m.find(&x); return 0; }

Compiling with headers:

$ clang++ -std=c++23 use.cpp -DUSE_HEADERS -o Hello.out $ ./Hello.out Hello World!

With modules:

$ clang++ -std=c++23 --precompile hello.cxxm -o M-hello.pcm $ clang++ -std=c++23 use.cpp -fmodule-file=Hello=M-hello.pcm M-hello.pcm -o Hello_mod.out

results in

/usr/include/boost/unordered/detail/foa/core.hpp:293:7: error: no matching function for call to '_mm_cmpeq_epi8' 293 | _mm_cmpeq_epi8(load_metadata(),_mm_setzero_si128()))&0x7FFF; | ^~~~~~~~~~~~~~ /usr/include/boost/unordered/detail/foa/core.hpp:309:14: note: in instantiation of member function 'boost::unordered::detail::foa::group15<boost::unordered::detail::foa::plain_integral>::match_available' requested here 309 | return (~match_available())&0x7FFF; 

I could file this as a boost_unordered issue or make a PR there, as I've generally found I can work around the problem.
But I'll see about creating a minimal reproducer using #include <immintrin.h> directlry that works with headers but fails with modules.