Missing builtins MSVC

[Harry Gillanders]

On Saturday, 5 September 2026 at 14:20:08 UTC, Danny Arends wrote:
> Hey All,
>
> Was trying to use importC with the latest MSVC runtime (Visual 
> Studio/Build tools 2026), and got the following linker issues 
> (all related to ucrt\wchar.h and ucrt\string.h). Missing from 
> `Windows Kits\10\Include\10.0.26100.0`:
>
> Error: undefined reference to `_mm_cvtsi32_si128` referenced 
> from `wmemchr`
> Error: undefined reference to `_mm256_broadcastw_epi16` 
> referenced from `wmemchr`
> Error: undefined reference to `_mm256_loadu_si256` referenced 
> from `wmemchr`
> Error: undefined reference to `_mm256_cmpeq_epi16` referenced 
> from `wmemchr`
> Error: undefined reference to `_mm256_movemask_epi8` referenced 
> from `wmemchr`
> Error: undefined reference to `_BitScanForward` referenced from 
> `wmemchr`
> Error: undefined reference to `_mm_set1_epi16` referenced from 
> `wmemchr`
> Error: undefined reference to `_mm_loadu_si128` referenced from 
> `wmemchr`
> Error: undefined reference to `_mm_cmpeq_epi16` referenced from 
> `wmemchr`
> Error: undefined reference to `_mm_movemask_epi8` referenced 
> from `wmemchr`
> Error: undefined reference to `_mm_loadl_epi64` referenced from 
> `wmemchr`
> Error: undefined reference to `_BitScanForward64` referenced 
> from `wmemcmp`
>
> I can see from DRuntime that `_BitScanForward` and 
> `_BitScanForward64` forward were already added since DMD 
> v2.113.0 was released.
>
> Also, MSVC toolset 2026 defines `__check_arch_support`, whose 
> body references the compiler-emitted constants 
> `__arch_avx10ver` and `__arch_inverted`. MSVC codegen stamps 
> these per object from its flags, but ImportC does not emit 
> them, so they are unresolved even on an older SDK.
>
>
> Will the _mm* functions be added to __builtins_msvc.d at some 
> point ?

As you noted, the `_BitScan` intrinsics are implemented in DMD 
nightly, and will be released alongside D v2.114.

The \_mm intrinsics are x86/Intel SIMD intrinsics, and given the 
state of `core.simd` I consider it unlikely that D proper will 
ever support those intrinsics—never mind ImportC!

I haven't tried this myself, but it may be possible to use 
Guillaume Piolat's (excellent) 
[intel-intrinsics](https://code.dlang.org/packages/intel-intrinsics) library to make those intrinsics available to ImportC by `__import`ing the `inteli` module.

Ideally, something like this:
```
#include <importc_msvc_builtins.h>
__import inteli;
#include <ucrt/wchar.h>
```
would work, but I don't know how D/intel-intrinsics' vector types 
interact with C's vector types.


I haven't looked into the arch detection/querying symbols too 
deeply: but it shouldn't be terribly difficult to define those ad 
hoc before including any headers that use them, as an interim 
solution.