diff --git a/libc/cmake/modules/LLVMLibCCheckCpuFeatures.cmake b/libc/cmake/modules/LLVMLibCCheckCpuFeatures.cmake
new file mode 100644
--- /dev/null
+++ b/libc/cmake/modules/LLVMLibCCheckCpuFeatures.cmake
@@ -0,0 +1,35 @@
+# Sets variables of the form CPU_FEATURES_XXX
+# Where XXX is the uppercase name of the feature.
+#
+# Usage:
+# include(LLVMLibCCheckCpuFeatures)
+# if(${CPU_FEATURES_AVX2})
+#    ...
+# endif()
+function(check_cpu_features)
+    if(${CMAKE_HOST_APPLE})
+        execute_process(
+            COMMAND sysctl -a
+            COMMAND grep machdep.cpu.features
+            COMMAND cut -f2 -d:
+            COMMAND tr . _
+            OUTPUT_VARIABLE flags_string
+        )
+    elseif(${CMAKE_HOST_UNIX})
+        execute_process(
+            COMMAND grep -h -m1 \\w*flags\\w* /proc/cpuinfo
+            COMMAND cut -f2 -d:
+            OUTPUT_VARIABLE flags_string
+        )
+    else()
+        message(FATAL "Unsupported system")
+    endif()
+
+    string(REPLACE " " ";" flags "${flags_string}")
+    foreach(flag ${flags})
+        string(TOUPPER ${flag} uppercase_flag)
+        set(CPU_FEATURES_${uppercase_flag} true PARENT_SCOPE)
+    endforeach()
+endfunction()
+
+check_cpu_features()