[cmake] AVX not detected on macos

[themightyoarfish]

I am compiling the current master c1835f4.

System is macos 10.15.7. The cmake configuration process does not pick up on the fact that both AVX and AVX2 should be available:

 > cmake ..                 -DBUILD_io=ON                 -DWITH_VTK=ON -DBUILD_kdtree=ON                 -DBUILD_visualization=ON -DBUILD_octree=ON                 -DBUILD_io=ON                 -DBUILD_filters=ON -DBUILD_surface=ON                 -DBUILD_CUDA=OFF                 -DBUILD_GPU=OFF -DBUILD_examples=OFF                 -DBUILD_features=ON -DBUILD_tools=ON                 -DBUILD_keypoints=OFF                 -DBUILD_ml=OFF -DBUILD_outofcore=OFF                 -DBUILD_people=OFF -DBUILD_tracking=OFF                 -DBUILD_registration=ON                 -DBUILD_recognition=OFF                 -DBUILD_stereo=OFF                 -DBUILD_ml=ON  -DBUILD_tools=ON -DBUILD_recognition=ON -DBUILD_keypoints=ON -DBUILD_apps=ON -DBUILD_apps_pointcloud_editor=ON-- The C compiler identification is AppleClang 12.0.0.12000032
-- The CXX compiler identification is AppleClang 12.0.0.12000032
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/local/opt/ccache/libexec/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/local/opt/ccache/libexec/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Found PkgConfig: /usr/local/bin/pkg-config (found version "0.29.2") 
-- Found ClangFormat: /usr/local/bin/clang-format (found suitable version "13.0.0", minimum required is "10") 
-- Adding target 'format'
-- Performing Test HAVE_MM_MALLOC
-- Performing Test HAVE_MM_MALLOC - Success
-- Performing Test HAVE_POSIX_MEMALIGN
-- Performing Test HAVE_POSIX_MEMALIGN - Success
-- Performing Test HAVE_SSE4_2_EXTENSIONS
-- Performing Test HAVE_SSE4_2_EXTENSIONS - Failed
-- Performing Test HAVE_SSE4_1_EXTENSIONS
-- Performing Test HAVE_SSE4_1_EXTENSIONS - Success
-- Performing Test HAVE_AVX2
-- Performing Test HAVE_AVX2 - Failed			# <-------- here
-- Performing Test HAVE_AVX
-- Performing Test HAVE_AVX - Failed

My cpu supports both AVX 1.0 and AVX2:

> /usr/sbin/sysctl -n machdep.cpu.features machdep.cpu.leaf7_features
[…] AVX1.0 […] AVX2 […]

[themightyoarfish]

The first interesting observations is that in cmake/pcl_find_avx.cmake, CMAKE_COMPILER_IS_CLANG is false, no matter if I use ccache or Apple's default compiler.

This leads to CMAKE_REQUIRED_FLAGS not getting set and hence check_cxx_source_runs() tries to compile without -march=native which fails.

[themightyoarfish]

Solution:

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 63721efc7..84c9f5de4 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -47,7 +47,7 @@ set(CMAKE_BUILD_TYPE "${CMAKE_BUILD_TYPE}" CACHE STRING
 # Compiler identification
 # Define a variable CMAKE_COMPILER_IS_X where X is the compiler short name.
 # Note: CMake automatically defines one for GNUCXX, nothing to do in this case.
-if(CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
+if(CMAKE_CXX_COMPILER_ID MATCHES ".*Clang.*")
   set(CMAKE_COMPILER_IS_CLANG 1)
 elseif(__COMPILER_PATHSCALE)
   set(CMAKE_COMPILER_IS_PATHSCALE 1)

The check tests for exact compiler name, but on macos, the compiler is not Clang but AppleClang.

[mvieth]

Could you take a look at #3131 ? If it looks good to you we could perhaps merge it soon

[themightyoarfish]

Well I can see that using that branch, optimizations are detected

-- Using CPU native flags for SSE optimization: -march=native

Cant's speak to the other changes in that PR.
With my fix here, I'm getting more flags, but that's probably because I'm basing on current master, and #3131 is some time behind.

-- -ftemplate-depth=1024 -Qunused-arguments -Wno-invalid-offsetof -msse4.2 -mfpmath=sse -march=native -mavx2 -Xclang -fopenmp

[mvieth]

Fixed by pull request #5153