Print warning if incompatible alignment option chosen

Users repeatedly report segmentation faults coming from Memory.h in the Eigen code (aligned_free/handmade_aligned_free). This is because PCL uses Eigen's handmade_aligned_malloc but user code does not use the corresponding handmade_aligned_free (or the other way around), due to chosen SSE/AVX flags and the resulting alignment requirements. PCL's CMake config handles this by automatically setting SSE/AVX options in the user project as they are used in PCL, but not everyone uses CMake. This commit adds a check within PCL's header files for this kind of incompatibility.

At first I considered solving theses incompatibilities automatically by setting EIGEN_MALLOC_ALREADY_ALIGNED and EIGEN_MAX_ALIGN_BYTES, but that would have been more complex and error-prone, so I decided only for checking and warning.

I would have preferred `#warning` which however is not available on MSVC. `#pragma message` is an option on MSVC, but this is too easily overlooked IMO. Users have the option to silence this by defining the `PCL_SILENCE_MALLOC_WARNING` macro (in case of false positive).

CMakeLists.txt

@@ -440,6 +440,21 @@ if(WITH_SYSTEM_CJSON)
   endif()
 endif()
 
+set(CMAKE_REQUIRED_LIBRARIES Eigen3::Eigen) # so that Eigen/Core is found below
+CHECK_CXX_SOURCE_COMPILES("
+#include <Eigen/Core>
+#if (EIGEN_DEFAULT_ALIGN_BYTES==0) || EIGEN_MALLOC_ALREADY_ALIGNED
+#error Eigen will not use handmade_aligned_malloc (which is fine, we just throw an error here to make this compilation fail)
+#endif
+int main() { return 0; }"
+PCL_USES_EIGEN_HANDMADE_ALIGNED_MALLOC)
+if (PCL_USES_EIGEN_HANDMADE_ALIGNED_MALLOC) # CHECK_CXX_SOURCE_COMPILES does not necessarily set this to 0 or 1
+  set(PCL_USES_EIGEN_HANDMADE_ALIGNED_MALLOC 1)
+else()
+  set(PCL_USES_EIGEN_HANDMADE_ALIGNED_MALLOC 0)
+endif()
+unset(CMAKE_REQUIRED_LIBRARIES)
+
 ### ---[ Create the config.h file
 set(pcl_config_h_in "${CMAKE_CURRENT_SOURCE_DIR}/pcl_config.h.in")
 set(pcl_config_h "${CMAKE_CURRENT_BINARY_DIR}/include/pcl/pcl_config.h")

common/include/pcl/memory.h

@@ -44,13 +44,28 @@
  */
 
 #include <pcl/type_traits.h>  // for has_custom_allocator
+#include <pcl/pcl_config.h> // for PCL_USES_EIGEN_HANDMADE_ALIGNED_MALLOC
 
 #include <Eigen/Core>  // for EIGEN_MAKE_ALIGNED_OPERATOR_NEW
 
 #include <memory>  // for std::allocate_shared, std::dynamic_pointer_cast, std::make_shared, std::shared_ptr, std::static_pointer_cast, std::weak_ptr
 #include <type_traits>  // for std::enable_if_t, std::false_type, std::true_type
 #include <utility>  // for std::forward
 
+#if !defined(PCL_SILENCE_MALLOC_WARNING)
+#if PCL_USES_EIGEN_HANDMADE_ALIGNED_MALLOC
+// EIGEN_DEFAULT_ALIGN_BYTES and EIGEN_MALLOC_ALREADY_ALIGNED will be set after including Eigen/Core
+// this condition is the same as in the function aligned_malloc in Memory.h in the Eigen code
+#if (defined(EIGEN_DEFAULT_ALIGN_BYTES) && EIGEN_DEFAULT_ALIGN_BYTES==0) || (defined(EIGEN_MALLOC_ALREADY_ALIGNED) && EIGEN_MALLOC_ALREADY_ALIGNED)
+#error "Potential runtime error due to aligned malloc mismatch! You likely have to compile your code with AVX enabled or define EIGEN_MAX_ALIGN_BYTES=32"
+#endif
+#else // PCL_USES_EIGEN_HANDMADE_ALIGNED_MALLOC
+#if (defined(EIGEN_DEFAULT_ALIGN_BYTES) && EIGEN_DEFAULT_ALIGN_BYTES!=0) && (defined(EIGEN_MALLOC_ALREADY_ALIGNED) && !EIGEN_MALLOC_ALREADY_ALIGNED)
+#error "Potential runtime error due to aligned malloc mismatch! PCL was likely compiled without AVX support but you enabled AVX for your code"
+#endif
+#endif // PCL_USES_EIGEN_HANDMADE_ALIGNED_MALLOC
+#endif // !defined(PCL_SILENCE_MALLOC_WARNING)
+
 /**
  * \brief Macro to signal a class requires a custom allocator
  *

pcl_config.h.in

@@ -35,6 +35,8 @@
   #endif //PCL_MINOR_VERSION
 #endif 
 
+#define PCL_USES_EIGEN_HANDMADE_ALIGNED_MALLOC ${PCL_USES_EIGEN_HANDMADE_ALIGNED_MALLOC}
+
 #cmakedefine HAVE_OPENNI 1
 
 #cmakedefine HAVE_OPENNI2 1