From ef799a9b423babc4e3ece31b8d8f3d84a94be0fa Mon Sep 17 00:00:00 2001
From: Xavier Arteaga <xavier@softwareradiosystems.com>
Date: Wed, 18 Nov 2020 11:02:14 +0100
Subject: [PATCH] Avoid GCC native architecture for AVX512 CPUs when AVX512 is
 disabled

---
 CMakeLists.txt              |  4 ++--
 cmake/modules/FindSSE.cmake | 14 ++++++++++++++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index bf0284dd6..dd15dff7c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -406,8 +406,8 @@ if(CMAKE_C_COMPILER_ID MATCHES "GNU" OR CMAKE_C_COMPILER_ID MATCHES "Clang")
   endif (HAVE_FMA)
 
   if (HAVE_AVX512)
-    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -march=${GCC_ARCH} -mavx512f -mavx512cd -mavx512bw -mavx512dq -DLV_HAVE_AVX512")
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -march=${GCC_ARCH} -mavx512f -mavx512cd -mavx512bw -mavx512dq -DLV_HAVE_AVX512")
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -mavx512f -mavx512cd -mavx512bw -mavx512dq -DLV_HAVE_AVX512")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -mavx512f -mavx512cd -mavx512bw -mavx512dq -DLV_HAVE_AVX512")
   endif(HAVE_AVX512)
 
   if(NOT ${CMAKE_BUILD_TYPE} STREQUAL "Debug")
diff --git a/cmake/modules/FindSSE.cmake b/cmake/modules/FindSSE.cmake
index 24fc23662..846cd8aa7 100644
--- a/cmake/modules/FindSSE.cmake
+++ b/cmake/modules/FindSSE.cmake
@@ -168,6 +168,20 @@ if (ENABLE_SSE)
         if (HAVE_AVX512)
             message(STATUS "AVX512 is enabled - target CPU must support it")
         endif()
+    elseif (${GCC_ARCH} MATCHES "native" AND CMAKE_CXX_COMPILER_ID MATCHES "GNU")
+        # When GCC flag -march=native and the CPU supports AVX512 (skylake-avx512 architecture), GCC uses AVX512 instructions
+        # automatically, independently of the rest of flags.
+
+        # Get the CPU architecture
+        execute_process(COMMAND ${CMAKE_C_COMPILER} -march=native -Q --help=target
+                OUTPUT_VARIABLE DETECT_SKYLAKE_AVX512)
+
+        # Check if the native architecture matches with skylake-avx512
+        if (${DETECT_SKYLAKE_AVX512} MATCHES "march=.*skylake-avx512")
+            # Force skylake architecture without AVX512
+            set(GCC_ARCH "skylake")
+            message(STATUS "This is a skylake-avx512 CPU, as AVX512 was disabled the architecture will be set to skylake")
+        endif (${IS_SKYLAKE_AVX512})
     endif()