use KNL-specific compiler flags for KNL target

added flags for GNU and Intel compilers to the cmake build rules
that generate KNL-specific instructions when the TARGET_KNL cmake
flag is set.

CMakeLists.txt

@@ -62,6 +62,12 @@ if(SYSTEM_CRAY)
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -dynamic")
 endif()
 
+# Cray systems
+set(TARGET_KNL OFF CACHE BOOL "target Intel KNL architecture")
+if(TARGET_KNL)
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${CXXOPT_KNL}")
+endif()
+
 # targets for extermal dependencies
 include(ExternalProject)
 externalproject_add(modparser

cmake/CompilerOptions.cmake

@@ -13,10 +13,21 @@ if(${CMAKE_CXX_COMPILER_ID} MATCHES "Clang")
     set(CXXOPT_WALL "${CXXOPT_WALL} -Wno-missing-braces")
 endif()
 
+if(${CMAKE_CXX_COMPILER_ID} MATCHES "GNU")
+
+    # compiler flags for generating KNL-specific AVX512 instructions
+    # supported in gcc 4.9.x and later
+    #set(CXXOPT_KNL "-mavx512f")
+    set(CXXOPT_KNL "-march=knl")
+endif()
+
 if(${CMAKE_CXX_COMPILER_ID} MATCHES "Intel")
     # Disable warning for unused template parameter
     # this is raised by a templated function in the json library
 
     set(CXXOPT_WALL "${CXXOPT_WALL} -wd488")
+
+    # compiler flags for generating KNL-specific AVX512 instructions
+    set(CXXOPT_KNL "-xMIC-AVX512")
 endif()