Recover lost SSE2 support on MSVC 64-bit builds; FFTW_VERSION

[olafk1]

For MSVC, the HAVE_SSE2 preprocessor definition will only be enabled in CMakeLists.txt if the compiler successfully accepts /arch:SSE2 as a command line parameter. However, this applies to MSVC 32-bit compilers only. MSVC 64-bit compilers have the switch /arch:SSE2 removed, since this is already the default minimum architecture supported on all 64-bit CPUs (see Microsoft Docs here).

As a result, fftw DLLs lose all SSE2 support when the common configuration -DENABLE_SSE2=1 -DENABLE_AVX=1 is passed to cmake. This leads to an illegal instruction and a crash during runtime on non-AVX-CPUs.

The following patch should at least re-enable SSE2 support for MSVC 64-bit compilers, although /arch:SSE2 has been removed as the default minimum architecture.

diff --git a/CMakeLists.txt b/CMakeLists.txt
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -194,2 +194,7 @@

+# Activate SSE2 support even if the corresponding compiler flag for 64-bit MSVC has been removed
+if (CMAKE_CL_64 AND ENABLE_SSE2)
+  set (HAVE_SSE2 TRUE)
+endif ()
+
 if (HAVE_SSE2 OR HAVE_AVX)

Side note: the version number in CMakeLists.txt version 3.3.10 wrongly indicates FFTW_VERSION 3.3.9 and needs a brush up.

[olafk1]

The fix above addresses a significant performance flaw in MSVC non-AVX builds for 64-bit systems. It turned out that very common SSE2/AVX builds (like that from conda-forge) still crash on some older 64-bit CPUs. This is caused by a bigger conceptual bug in CMakeList.txt, which should be discussed in another ticket, because upcoming CPU architectures are now also affected.

[egpbos]

This makes sense. Have the maintainers seen this? @matteo-frigo