CMake: Expose Python LTO Control

Before, LTO/IPO was default-enabled for the Python bindings.
This can sometimes, e.g. on PPC64le with GCC 6.4.0 on Summit, cause
problems in complex enough scenarios and fail to link.

We now expose control via the standardized CMake variable
`CMAKE_INTERPROCEDURAL_OPTIMIZATION`. This variable populates the
`INTERPROCEDURAL_OPTIMIZATION` property of targets but only works
really reliably with CMake 3.18+. We keep the default logic to use
LTO, use the `pybind11::lto` target for older CMake but let the user
deactivate the Python LTO by setting the
`CMAKE_INTERPROCEDURAL_OPTIMIZATION` variable to false.

Author: ax3l

CHANGELOG.rst

@@ -25,6 +25,7 @@ Other
 
 - ADIOS2: require version 2.7.0+ #927
 - pybind11: require version 2.6.2+ #977
+- CMake: Expose Python LTO Control #980
 
 
 0.13.4

CMakeLists.txt

@@ -606,7 +606,24 @@ if(openPMD_HAVE_PYTHON)
         src/binding/python/UnitDimension.cpp
     )
     target_link_libraries(openPMD.py PRIVATE openPMD)
-    target_link_libraries(openPMD.py PRIVATE pybind11::module pybind11::lto pybind11::windows_extras)
+    target_link_libraries(openPMD.py PRIVATE pybind11::module pybind11::windows_extras)
+
+    # LTO/IPO: CMake target properties work well for 3.18+ and are buggy before
+    set(_USE_PY_LTO ON)  # default shall be ON
+    if(DEFINED CMAKE_INTERPROCEDURAL_OPTIMIZATION)  # overwrite default if defined
+        if(NOT CMAKE_INTERPROCEDURAL_OPTIMIZATION)
+            set(_USE_PY_LTO OFF)
+        endif()
+    endif()
+    if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.18)
+        set_target_properties(openPMD.py PROPERTIES
+            INTERPROCEDURAL_OPTIMIZATION ${_USE_PY_LTO})
+    else()
+        if(_USE_PY_LTO)
+            target_link_libraries(openPMD.py PRIVATE pybind11::lto)
+        endif()
+    endif()
+    unset(_USE_PY_LTO)
 
     pybind11_extension(openPMD.py)
     pybind11_strip(openPMD.py)

setup.py

@@ -69,6 +69,9 @@ def build_extension(self, ext):
             # Windows: has no RPath concept, all `.dll`s must be in %PATH%
             #          or same dir as calling executable
         ]
+        if CMAKE_INTERPROCEDURAL_OPTIMIZATION is not None:
+            cmake_args.append('-DCMAKE_INTERPROCEDURAL_OPTIMIZATION=' +
+                              CMAKE_INTERPROCEDURAL_OPTIMIZATION)
         if sys.platform == "darwin":
             cmake_args.append('-DCMAKE_INSTALL_RPATH=@loader_path')
         else:
@@ -133,6 +136,8 @@ def build_extension(self, ext):
                                BUILD_TESTING)
 BUILD_EXAMPLES = os.environ.get('openPMD_BUILD_EXAMPLES',
                                 BUILD_EXAMPLES)
+CMAKE_INTERPROCEDURAL_OPTIMIZATION = os.environ.get(
+    'CMAKE_INTERPROCEDURAL_OPTIMIZATION', None)
 
 # https://cmake.org/cmake/help/v3.0/command/if.html
 if openPMD_USE_MPI.upper() in ['1', 'ON', 'TRUE', 'YES']: