Detect AVX & SSE and only build corresponding parts

Previously, the CMake configuration was such that it would always
build the AVX2, AVX512 & SSE2 Pybind11 modules without testing whether
the current system supported those options. The changes here use CMake
features to detect whether the architectural features are in fact
available, and only attempt to build the appropriate modules.

In addition, there is a minor bit of refactoring to group some of the
code more logically, and to add some more informational message
printouts.

Author: mhucka

CMakeLists.txt

@@ -15,13 +15,19 @@
 cmake_minimum_required(VERSION 3.31)
 project(qsim LANGUAGES CXX)
 
-include(CheckLanguage)
-check_language(CUDA)
-
 # This text is prepended to messages printed by this config file so it's
 # easier to figure out what came from where in the logs.
 set(MSG_PREFIX "[qsim cmake configuration]")
 
+
+# ~~~~~ Analyze the host's hardware & software features ~~~~~
+
+include(CheckLanguage)
+include(CheckCXXCompilerFlag)
+include(CheckCXXSourceRuns)
+
+check_language(CUDA)
+
 # CMake normally sets CMAKE_APPLE_SILICON_PROCESSOR on Apple Silicon; however,
 # it doesn't happen when running builds using cibuildwheel, even on Apple
 # Silicon. We have had better luck checking and seting it ourselves.
@@ -54,6 +60,23 @@ endif()
 
 find_package(OpenMP REQUIRED)
 
+cmake_host_system_information(RESULT HAVE_SSE2 QUERY HAS_SSE2)
+
+if(WIN32)
+    check_cxx_compiler_flag("/arch:AVX2" HAVE_AVX512)
+    check_cxx_compiler_flag("/arch:AVX512" HAVE_AVX512)
+else()
+    check_cxx_compiler_flag("-mavx2" HAVE_AVX2)
+    check_cxx_compiler_flag("-mavx512f" HAVE_AVX512)
+endif()
+
+
+# ~~~~~ Configure the build ~~~~~
+
+# The following settings mirror what is in our hand-written Makefiles.
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_POSITION_INDEPENDENT_CODE ON)
+
 # Always build the basic part.
 add_subdirectory(pybind_interface/basic)
 add_subdirectory(pybind_interface/decide)
@@ -69,16 +92,25 @@ if(NOT CMAKE_APPLE_SILICON_PROCESSOR)
         add_subdirectory(pybind_interface/hip)
     endif()
 
-    add_subdirectory(pybind_interface/sse)
-    add_subdirectory(pybind_interface/avx512)
-    add_subdirectory(pybind_interface/avx2)
+    if(HAVE_SSE2)
+      add_subdirectory(pybind_interface/sse)
+    endif()
+
+    if(HAVE_AVX2)
+      add_subdirectory(pybind_interface/avx2)
+    endif()
+
+    if(HAVE_AVX512)
+      add_subdirectory(pybind_interface/avx512)
+    endif()
 endif()
 
-# Additional miscellanous settings.
-# The following settings mirror what is in our hand-written Makefiles.
-set(CMAKE_CXX_STANDARD 17)
-set(CMAKE_POSITION_INDEPENDENT_CODE ON)
 
-# Print additional useful info.
-message(STATUS "${MSG_PREFIX} OpenMP found = ${OPENMP_FOUND}")
+# ~~~~~ Print misc. info ~~~~~
+
+message(STATUS "${MSG_PREFIX} host has SSE2 = ${HAVE_SSE2}")
+message(STATUS "${MSG_PREFIX} host has AVX2 = ${HAVE_AVX2}")
+message(STATUS "${MSG_PREFIX} host has AVX512 = ${HAVE_AVX512}")
+
 message(STATUS "${MSG_PREFIX} shell $PATH = $ENV{PATH}")
+message(STATUS "${MSG_PREFIX} shell $CUQUANTUM_ROOT = $ENV{CUQUANTUM_ROOT}")