From 67177ee3fb0c8357ebc7aa0f9c92f26f16dd4758 Mon Sep 17 00:00:00 2001
From: "John L. Jolly" <john.jolly@utah.edu>
Date: Mon, 23 May 2022 10:58:26 -0600
Subject: [PATCH] [CMakeLists.txt] Fix BUILD_ARCH option

The CMake option function is intended for ON/OFF operations. When using
"native" as a default, option would set BUILD_ARCH to "OFF" if not used
on the command line. This would cause the build architecture detection
to fail.

In this fix the option function is used properly and, if not used on the
command line, sets a default of "native". Also, if neither -march or
-mcpu work successfully, "native" is used as a fall-back.
---
 CMakeLists.txt | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 74a6313..579a795 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -99,7 +99,13 @@ endif ()
 # Avoid using O3
 set(CMAKE_CXX_FLAGS_RELEASE "-O2 -DNDEBUG")
 
-option(BUILD_ARCH "Specify build architecture target" "native")
+option(BUILD_ARCH "Specify build architecture target" OFF)
+
+if (NOT BUILD_ARCH)
+    set(BUILD_ARCH "native")
+endif ()
+
+message(STATUS "Verifying ${BUILD_ARCH} build architecture")
 
 check_cxx_compiler_flag("-march=${BUILD_ARCH}" HAS_MARCH)
 if (HAS_MARCH)
@@ -111,6 +117,9 @@ else ()
     if (HAS_MCPU)
         message(STATUS "Using mcpu=${BUILD_ARCH}")
         set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -mcpu=${BUILD_ARCH}")
+    else ()
+        message(STATUS "Unable to use ${BUILD_ARCH} for build arch, defaulting to native")
+        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -march=native")
     endif ()
 endif ()