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ADR-0521: MSVC portability gating — vif_avx512.c noinline/noclone + yuv_input.c S_ISREG/fstat

  • Status: Accepted
  • Date: 2026-05-18
  • Deciders: lusoris
  • Tags: ci, build, windows, msvc, simd, tools, portability, fork-local, bugfix

Context

After PR #1274 (ADR-0515) fixed the MinGW64 leg by replacing the /tmp-hardcoded mkstemp call, the Build — Windows MSVC + CUDA and Build — Windows MSVC + oneAPI SYCL matrix legs remained red on master for two distinct reasons:

MSVC+CUDA failure (vif_avx512.c): core/src/feature/x86/vif_avx512.c used the GCC/Clang extension __attribute__((noinline, noclone)) on two private helpers (vif_subsample_rd_8_vert_j, vif_subsample_rd_8_horiz_j) introduced by ADR-0503 to isolate register pressure in the AVX-512 VIF kernel. MSVC's cl.exe does not support __attribute__ syntax at all — it raises C2143: syntax error: missing ')' before '(' and cascades into ~80 downstream C2065: undeclared identifier errors for every parameter in the function body.

MSVC+SYCL failure (yuv_input.c): core/tools/yuv_input.c::yuv_check_file_size called fstat() and S_ISREG() on the return of fileno(fin). The file already guarded <unistd.h> and fileno → _fileno correctly, but S_ISREG is a POSIX macro not defined by MSVC's <sys/stat.h>. Intel's oneAPI SYCL compiler (icx-cl) enforces ISO C99 strictness and treats the implicit-function call as a hard error (error: call to undeclared function 'S_ISREG'). fstat itself is also a POSIX name; the MSVC equivalent is _fstat64 / struct __stat64. off_t is defined but is 32-bit on MSVC by default, which would truncate sizes above 2 GiB.

Neither issue surfaced before PR #1274 because:

  • The vif_avx512.c helper functions were introduced in PR #1261 (ADR-0503, merged just prior).
  • The yuv_input.c S_ISREG check was added post-PR #1274 or was previously masked by the CUDA build stopping earlier on a different error.

MSVC builds are "build only" (no test run) in the CI matrix; the Windows MSVC legs exist to prove the header and source surface compiles clean under cl.exe and icx-cl, catching portability regressions before they affect downstream integrators who target Windows natively.

Decision

vif_avx512.c: Define a VMAF_NOINLINE_NOCLONE portability macro at the top of the TU, immediately after the #define MAX line:

#if defined(_MSC_VER)
#define VMAF_NOINLINE_NOCLONE __declspec(noinline)
#elif defined(__GNUC__) || defined(__clang__)
#define VMAF_NOINLINE_NOCLONE __attribute__((noinline, noclone))
#else
#define VMAF_NOINLINE_NOCLONE
#endif

Replace both static __attribute__((noinline, noclone)) void declarations with static VMAF_NOINLINE_NOCLONE void. The noclone semantic is meaningful only on GCC (prevents constant-propagated clone synthesis); MSVC does not clone, so __declspec(noinline) is sufficient there.

yuv_input.c: Extend the existing #ifdef _WIN32 block to define POSIX aliases for fstat, struct stat, S_ISREG, and off_t that map to their MSVC equivalents:

#define fstat(fd, st)  _fstat64((fd), (st))
#define stat           __stat64
#define S_ISREG(m)     (((m) & _S_IFMT) == _S_IFREG)
typedef __int64 off_t;

This keeps the function body of yuv_check_file_size() unguarded and portable, and ensures file-size arithmetic is 64-bit on MSVC.

Alternatives considered

Option Pros Cons Why not chosen
Wrap vif_avx512.c helpers in #ifndef _MSC_VER no-ops No macro footprint Leaves the noinline hint absent on all non-GCC/Clang compilers; alters the register-pressure isolation that ADR-0503 depends on Drops the benefit on any future cl.exe-based SIMD path
Wrap entire yuv_check_file_size body in #ifndef _WIN32 Minimal LOC change Silently disables the file-size safety check on Windows builds The check is exactly the kind of misuse-guard that matters on all platforms
Use #pragma comment(lib, ...) + _fstat64 inline without a macro Slightly more explicit Pollutes the function body with #ifdef _WIN32 guards around every POSIX name Makes future readers untangle three interleaved branches instead of one

Consequences

  • Positive: Both MSVC+CUDA and MSVC+SYCL CI legs compile clean. The register-pressure isolation from ADR-0503 is preserved on GCC/Clang; MSVC gets __declspec(noinline) which is sufficient to prevent inlining. File-size checking in yuv_check_file_size works correctly on MSVC with 64-bit arithmetic.
  • Negative: None material. The VMAF_NOINLINE_NOCLONE macro is TU-scoped (not public), so it does not pollute the public header surface.
  • Neutral: The #define stat __stat64 alias in the _WIN32 block must not be included in TUs that use stat() for directory-entry testing (struct layout differs from struct stat64 on GNU), but yuv_input.c only calls _fstat64 — no lstat or directory paths.

References