Fix for NEON support on Apple M1 processors

Fixes #362

CMakeLists.txt

@@ -57,6 +57,14 @@ set(CPACK_PACKAGE_VERSION_PATCH "${CHRONO_VERSION_PATCH}")
 # Version as a hexadecimal integer of the form 0x00MMmmPP
 set(CH_VERSION 0x00070000)
 
+#-----------------------------------------------------------------------------
+# Detect operating system and processor for host and target
+#-----------------------------------------------------------------------------
+message(STATUS "We are on a ${CMAKE_HOST_SYSTEM_NAME} system")
+message(STATUS "The host processor is ${CMAKE_HOST_SYSTEM_PROCESSOR}")
+message(STATUS "Building for a ${CMAKE_SYSTEM_NAME} system")
+message(STATUS "The target processor is ${CMAKE_SYSTEM_PROCESSOR}")
+
 #-----------------------------------------------------------------------------
 # Location of additional CMake scripts
 #-----------------------------------------------------------------------------

cmake/FindNEON.cmake

@@ -22,11 +22,15 @@ if(CMAKE_COMPILER_IS_GNUCC OR CMAKE_COMPILER_IS_GNUCXX)
   execute_process(COMMAND ${CMAKE_CXX_COMPILER} "-dumpversion" OUTPUT_VARIABLE GCC_VERSION_STRING)
   if(GCC_VERSION_STRING VERSION_GREATER 4.2 AND NOT APPLE AND NOT CMAKE_CROSSCOMPILING)
     SET(NEON_FLAGS "${NEON_FLAGS} -march=native")
-    message(STATUS "Using CPU native flags for NEON optimization: ${NEON_FLAGS}")
+    message(STATUS "  Trying NEON optimization flags: ${NEON_FLAGS}")
   endif()
 elseif(CMAKE_CXX_COMPILER_ID MATCHES "Clang" AND NOT CMAKE_CROSSCOMPILING)
-    SET(NEON_FLAGS "${NEON_FLAGS} -march=native")
-    message(STATUS "Using CPU native flags for NEON optimization: ${NEON_FLAGS}")
+    if(APPLE)
+      SET(NEON_FLAGS "${NEON_FLAGS} -mcpu=apple-m1")
+    else()
+      SET(NEON_FLAGS "${NEON_FLAGS} -march=native")
+    endif()
+    message(STATUS "  Trying NEON optimization flags: ${NEON_FLAGS}")
 endif()
 
 include(CheckCXXSourceRuns)