From 050b0581b183ab7a0a6ccaf6a2e947700d8a93ee Mon Sep 17 00:00:00 2001
From: Sam Li <samli@nvidia.com>
Date: Tue, 14 Apr 2026 21:48:06 -0700
Subject: [PATCH] automatically detect and enable/disable AVX2

---
 CMakeLists.txt              | 14 +++++++++++++-
 src/sperr_helper.cpp        |  4 ----
 test_scripts/CMakeLists.txt |  6 ------
 3 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 161fdf4a..1fc367f1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -32,8 +32,20 @@ option( BUILD_SHARED_LIBS "Build shared SPERR library" ON )
 option( BUILD_UNIT_TESTS "Build unit tests using GoogleTest" ON )
 option( BUILD_CLI_UTILITIES "Build a set of command line utilities" ON )
 option( USE_OMP "Use OpenMP parallelization on 3D volumes" OFF )
-option( ENABLE_AVX2 "Enable AVX2 instruction set compilation" ON )
 option( SPERR_PREFER_RPATH "Set RPATH; this can fight with package managers so turn off when building for them" ON )
+
+#
+# AVX2 auto-detection: default ON for x86, OFF otherwise.
+#
+if(NOT DEFINED ENABLE_AVX2)
+  if(CMAKE_SYSTEM_PROCESSOR MATCHES "x86_64|AMD64|i[3-9]86")
+    option( ENABLE_AVX2 "Enable AVX2 instruction set compilation" ON )
+  else()
+    option( ENABLE_AVX2 "Enable AVX2 instruction set compilation" OFF )
+  endif()
+else()
+  option( ENABLE_AVX2 "Enable AVX2 instruction set compilation" ${ENABLE_AVX2} )
+endif()
 mark_as_advanced(FORCE SPERR_PREFER_RPATH)
 
 if(USE_OMP)
diff --git a/src/sperr_helper.cpp b/src/sperr_helper.cpp
index b72aae57..421b6c87 100644
--- a/src/sperr_helper.cpp
+++ b/src/sperr_helper.cpp
@@ -11,10 +11,6 @@
 #include <bit>
 #endif
 
-#ifdef __AVX2__
-#include <immintrin.h>
-#endif
-
 #ifdef USE_OMP
 #include <omp.h>
 #endif
diff --git a/test_scripts/CMakeLists.txt b/test_scripts/CMakeLists.txt
index d329dae6..0dbf6c50 100644
--- a/test_scripts/CMakeLists.txt
+++ b/test_scripts/CMakeLists.txt
@@ -1,12 +1,6 @@
 add_executable(        sperr_helper sperr_helper_unit_test.cpp )
 target_link_libraries( sperr_helper PUBLIC SPERR GTest::gtest_main )
 
-if(ENABLE_AVX2)
-  target_compile_options(sperr_helper PRIVATE
-                        "$<$<CXX_COMPILER_ID:MSVC>:/arch:AVX2>"
-                        "$<$<OR:$<CXX_COMPILER_ID:GNU>,$<CXX_COMPILER_ID:Clang>>:-mavx2;-mfma>")
-endif()
-
 add_executable(        bitstream bitstream_unit_test.cpp )
 target_link_libraries( bitstream PUBLIC SPERR GTest::gtest_main )