diff --git a/llvm/lib/Support/BLAKE3/CMakeLists.txt b/llvm/lib/Support/BLAKE3/CMakeLists.txt
index df18059185871b..4fd60a99bbfb14 100644
--- a/llvm/lib/Support/BLAKE3/CMakeLists.txt
+++ b/llvm/lib/Support/BLAKE3/CMakeLists.txt
@@ -53,12 +53,8 @@ if (CAN_USE_ASSEMBLER)
       disable_blake3_x86_simd()
     endif()
   else()
-    check_symbol_exists(__i386__ "" IS_X32)
-    if (IS_X32)
-      # blake3 C code autoenables SIMD for i386, but those implementations are
-      # only available via the intrinsics sources which we don't enable here.
-      disable_blake3_x86_simd()
-    else()
+    check_symbol_exists(__x86_64__ "" IS_X64)
+    if (IS_X64 OR CMAKE_OSX_ARCHITECTURES)
       # In a macOS Universal build (setting CMAKE_OSX_ARCHITECTURES to multiple
       # values), compilation of the source files will target multiple architectures
       # (each source file is internally compiled once for each architecture).
@@ -70,13 +66,11 @@ if (CAN_USE_ASSEMBLER)
         blake3_avx2_x86-64_unix.S
         blake3_avx512_x86-64_unix.S
       )
-      check_c_compiler_flag("-mavx512vl" SUPPORTS_avx512vl)
-      if (SUPPORTS_avx512vl)
-        # Clang-6 needs this flag. We also suppress '-Wunused-command-line-argument'
-        # in case the file is included with arm architecture.
-        set_source_files_properties(blake3_avx512_x86-64_unix.S
-          PROPERTIES COMPILE_OPTIONS "-mavx512vl;-Wno-unused-command-line-argument")
-      endif()
+      # Clang-6 needs this flag.
+      set_source_files_properties(blake3_avx512_x86-64_windows_gnu.S
+        PROPERTIES COMPILE_OPTIONS "-mavx512vl")
+    else()
+      disable_blake3_x86_simd()
     endif()
   endif()
 else()