Fix sm100 gemm wrong static constexpr that breaks compilation on Windows

[SystemPanic]

constexpr was incorrectly added to the function definition only for this architecture, breaking the compilation of Cutlass on Windows.

[hwu36]

@d-k-b

[github-actions]

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[d-k-b]

This looks like a symptom of another issue. What error did you see here?

[SystemPanic]

@d-k-b If defined(_MSC_VER) is not included, is_unsigned_v is missing.

For example, with the latest MSVC 2022 with CL 19.43.34810, it raises the following error:

include/cutlass/exmy_base.h(404): error: namespace "cutlass::platform" has no member "is_unsigned_v"
    static_assert(cutlass::platform::is_unsigned_v<Storage>, "Use an unsigned integer for StorageType");

Related: https://learn.microsoft.com/es-es/cpp/build/reference/zc-cplusplus?view=msvc-170

If -Xcompiler=/Zc:__cplusplus is added to NVCC, version is detected correctly without including defined(_MSC_VER)

I don't have the time to fully check if including defined(_MSC_VER) in this place is problematic when compiling Cutlass with a standard lower than C++17, in my limited tests, it's not.

If it's the case, tell me and I remove it from the PR.

[d-k-b]

The CUTLASS CMake code applies the __cplusplus flag to MSVC compilation automatically. Is the error being seen with a build outside of CMake? I'd prefer we revert this change for this PR and then if it's needed for some scenario we handle it in a separate request.

cutlass/CMakeLists.txt

Line 561 in 9d165a3

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /Zc:__cplusplus")

Suggested change

	#if defined(_MSC_VER) || (201703L <=__cplusplus)
	#if (201703L <= __cplusplus)

[SystemPanic]

Ok, I see where the problem is.

vLLM it's being built with CMake, but it's not adding CUTLASS in the standard way, so the MSVC specific flags

cutlass/CMakeLists.txt

Line 561 in 9d165a3

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /Zc:__cplusplus")

are not being applied at all.

Commit reverted.