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).

Author: mvieth

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 +44,36 @@
  */
 
 #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)
+#if defined(_MSC_VER)
+#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 (to silence this message at your own risk, define PCL_SILENCE_MALLOC_WARNING=1)"
+#else // defined(_MSC_VER)
+#warning "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 (to silence this message at your own risk, define PCL_SILENCE_MALLOC_WARNING=1)"
+#endif // defined(_MSC_VER)
+#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)
+#if defined(_MSC_VER)
+#error "Potential runtime error due to aligned malloc mismatch! PCL was likely compiled without AVX support but you enabled AVX for your code (to silence this message at your own risk, define PCL_SILENCE_MALLOC_WARNING=1)"
+#else // defined(_MSC_VER)
+#warning "Potential runtime error due to aligned malloc mismatch! PCL was likely compiled without AVX support but you enabled AVX for your code (to silence this message at your own risk, define PCL_SILENCE_MALLOC_WARNING=1)"
+#endif // defined(_MSC_VER)
+#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