Add Windows OpenMP 2.0 compatibility

CMakeLists.txt

@@ -1135,7 +1135,13 @@ endif()
 # --- #pragma omp simd flags (used for reference kernels only) ---
 if(PRAGMA_OMP_SIMD)
     if(WIN32)
-        set(COMPSIMDFLAGS /openmp:experimental)
+        # Check if using Clang with GNU-like command-line (not MSVC/Clang-CL)
+        if(CMAKE_C_COMPILER_ID STREQUAL "Clang" AND 
+           CMAKE_C_COMPILER_FRONTEND_VARIANT STREQUAL "GNU")
+            set(COMPSIMDFLAGS -fopenmp-simd)
+        else()
+            set(COMPSIMDFLAGS /openmp:experimental)
+        endif()
     else()
         set(COMPSIMDFLAGS -fopenmp-simd)
     endif()

frame/thread/bli_thread.c

@@ -35,6 +35,18 @@
 
 #include "blis.h"
 
+// OpenMP 2.0 compatibility: Provide fallbacks for OpenMP 3.0 functions
+// Microsoft Visual Studio's OpenMP only supports OpenMP 2.0
+// Note: omp.h is already included by blis.h when BLIS_ENABLE_OPENMP is defined
+#if defined(BLIS_ENABLE_OPENMP) && defined(_MSC_VER)
+static inline int omp_get_active_level(void) {
+    return 0;  // Always assume top-level (no nested parallelism support)
+}
+static inline int omp_get_max_active_levels(void) {
+    return 1;  // OpenMP 2.0 doesn't support nested parallelism
+}
+#endif
+
 thrinfo_t BLIS_PACKM_SINGLE_THREADED = {};
 thrinfo_t BLIS_GEMM_SINGLE_THREADED  = {};
 thrcomm_t BLIS_SINGLE_COMM           = {};