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Overhaul LTO flag detection

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Clang on linux currently fails to run cmake:

    $ CC=clang CXX=clang++ cmake ..
    ...
    -- Configuring done
    CMake Error at tools/pybind11Tools.cmake:135 (target_compile_options):
      Error evaluating generator expression:

        $<:-flto>

      Expression did not evaluate to a known generator expression
    Call Stack (most recent call first):
      tests/CMakeLists.txt:68 (pybind11_add_module)

But investigating this led to various other -flto detection problems;
this commit thus overhauls LTO flag detection:

- -flto needs to be passed to the linker as well
- Also compile with -fno-fat-lto-objects under GCC
- Pass the equivalent flags to MSVC
- Enable LTO flags for via generator expressions (for non-debug builds
  only), so that multi-config builds (like on Windows) still work
  properly.  This seems reasonable, however, even on single-config
  builds (and simplifies the cmake code a bit).
- clang's lto linker plugins don't accept '-Os', so replace it with
  '-O3' when doing a MINSIZEREL build
- Enable trying ThinLTO by default for test suite (only affects clang)
- Match Clang$ rather than ^Clang$ because, for cmake with 3.0+
  policies in effect, the compiler ID will be AppleClang on macOS.
This commit is contained in:
Jason Rhinelander 2017-01-17 02:13:11 -05:00 committed by Wenzel Jakob
parent bee8827a98
commit 1bee6e7df8
2 changed files with 77 additions and 48 deletions
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2
tests/CMakeLists.txt
View File

@ -65,7 +65,7 @@ if(PYBIND11_TEST_FILES_EIGEN_I GREATER -1)
endif() endif()
# Create the binding library # Create the binding library
pybind11_add_module(pybind11_tests pybind11_tests.cpp pybind11_add_module(pybind11_tests THIN_LTO pybind11_tests.cpp
${PYBIND11_TEST_FILES} ${PYBIND11_HEADERS}) ${PYBIND11_TEST_FILES} ${PYBIND11_HEADERS})
pybind11_enable_warnings(pybind11_tests) pybind11_enable_warnings(pybind11_tests)

123
tools/pybind11Tools.cmake
View File

@ -36,27 +36,63 @@ function(select_cxx_standard)
endif() endif()
endfunction() endfunction()
# Internal: find the appropriate LTO flag for this compiler # Internal: try compiling with the given c++ and linker flags; set success_out to 1 if it works
macro(_pybind11_find_lto_flag output_var prefer_thin_lto) function(_pybind11_check_cxx_and_linker_flags cxxflags linkerflags success_out)
if(${prefer_thin_lto}) set(CMAKE_REQUIRED_QUIET 1)
# Check for ThinLTO support (Clang) set(CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES} ${linkerflags})
check_cxx_compiler_flag("-flto=thin" HAS_THIN_LTO_FLAG) check_cxx_compiler_flag("${cxxflags}" has_lto)
set(${output_var} $<${HAS_THIN_LTO_FLAG}:-flto=thin>) set(${success_out} ${has_lto} PARENT_SCOPE)
endif() endfunction()
if(NOT ${prefer_thin_lto} OR NOT HAS_THIN_LTO_FLAG) # Wraps the above in a macro that sets the flags in the parent scope and returns if the check
if(NOT CMAKE_CXX_COMPILER_ID MATCHES "Intel") # succeeded (since this is a macro, not a function, the PARENT_SCOPE set and return is from the
# Check for Link Time Optimization support (GCC/Clang) # caller's POV)
check_cxx_compiler_flag("-flto" HAS_LTO_FLAG) macro(_pybind11_return_if_cxx_and_linker_flags_work feature cxxflags linkerflags cxx_out linker_out)
set(${output_var} $<${HAS_LTO_FLAG}:-flto>) _pybind11_check_cxx_and_linker_flags(${cxxflags} ${linkerflags} check_success)
else() if(check_success)
# Intel equivalent to LTO is called IPO set(${cxx_out} ${cxxflags} PARENT_SCOPE)
check_cxx_compiler_flag("-ipo" HAS_IPO_FLAG) set(${linker_out} ${linkerflags} PARENT_SCOPE)
set(${output_var} $<${HAS_IPO_FLAG}:-ipo>) message(STATUS "Found ${feature} flags: ${cxxflags}")
endif() return()
endif() endif()
endmacro() endmacro()
# Internal: find the appropriate link time optimization flags for this compiler
function(_pybind11_find_lto_flags cxxflags_out linkerflags_out prefer_thin_lto)
if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang")
set(cxx_append "")
set(linker_append "")
if (CMAKE_CXX_COMPILER_ID MATCHES "Clang" AND NOT APPLE)
# Clang Gold plugin does not support -Os; append -O3 to MinSizeRel builds to override it
set(linker_append "$<$<CONFIG:MinSizeRel>: -O3>")
elseif(CMAKE_CXX_COMPILER_ID MATCHES "GNU")
set(cxx_append " -fno-fat-lto-objects")
endif()
if (CMAKE_CXX_COMPILER_ID MATCHES "Clang" AND ${prefer_thin_lto})
_pybind11_return_if_cxx_and_linker_flags_work("LTO"
"-flto=thin${cxx_append}" "-flto=thin${linker_append}" ${cxxflags_out} ${linkerflags_out})
endif()
_pybind11_return_if_cxx_and_linker_flags_work("LTO"
"-flto${cxx_append}" "-flto${linker_append}" ${cxxflags_out} ${linkerflags_out})
elseif (CMAKE_CXX_COMPILER_ID MATCHES "Intel")
# Intel equivalent to LTO is called IPO
_pybind11_return_if_cxx_and_linker_flags_work("LTO"
"-ipo" "-ipo" ${cxxflags_out} ${linkerflags_out})
elseif(MSVC)
# cmake only interprets libraries as linker flags when they start with a - (otherwise it
# converts /LTCG to \LTCG as if it was a Windows path). Luckily MSVC supports passing flags
# with - instead of /, even if it is a bit non-standard:
_pybind11_return_if_cxx_and_linker_flags_work("LTO"
"/GL" "-LTCG" ${cxxflags_out} ${linkerflags_out})
endif()
set(${cxxflags_out} "" PARENT_SCOPE)
set(${linkerflags_out} "" PARENT_SCOPE)
message(STATUS "LTO disabled (not supported by the compiler and/or linker)")
endfunction()
# Build a Python extension module: # Build a Python extension module:
# pybind11_add_module(<name> [MODULE | SHARED] [EXCLUDE_FROM_ALL] # pybind11_add_module(<name> [MODULE | SHARED] [EXCLUDE_FROM_ALL]
# [NO_EXTRAS] [THIN_LTO] source1 [source2 ...]) # [NO_EXTRAS] [THIN_LTO] source1 [source2 ...])
@ -124,42 +160,35 @@ function(pybind11_add_module target_name)
return() return()
endif() endif()
if(NOT MSVC) # Find LTO flags
# Enable link time optimization and set the default symbol _pybind11_find_lto_flags(lto_cxx_flags lto_linker_flags ARG_THIN_LTO)
# visibility to hidden (very important to obtain small binaries) if (lto_cxx_flags OR lto_linker_flags)
string(TOUPPER "${CMAKE_BUILD_TYPE}" U_CMAKE_BUILD_TYPE) # Enable LTO flags if found, except for Debug builds
if (NOT ${U_CMAKE_BUILD_TYPE} MATCHES DEBUG) separate_arguments(lto_cxx_flags)
# Link Time Optimization separate_arguments(lto_linker_flags)
if(NOT CYGWIN) target_compile_options(${target_name} PRIVATE "$<$<NOT:$<CONFIG:Debug>>:${lto_cxx_flags}>")
_pybind11_find_lto_flag(lto_flag ARG_THIN_LTO) target_link_libraries(${target_name} PRIVATE "$<$<NOT:$<CONFIG:Debug>>:${lto_linker_flags}>")
target_compile_options(${target_name} PRIVATE ${lto_flag}) endif()
endif()
# Default symbol visibility # Set the default symbol visibility to hidden (very important to obtain small binaries)
target_compile_options(${target_name} PRIVATE "-fvisibility=hidden") if (NOT MSVC)
target_compile_options(${target_name} PRIVATE "-fvisibility=hidden")
# Strip unnecessary sections of the binary on Linux/Mac OS # Strip unnecessary sections of the binary on Linux/Mac OS
if(CMAKE_STRIP) if(CMAKE_STRIP)
if(APPLE) if(APPLE)
add_custom_command(TARGET ${target_name} POST_BUILD add_custom_command(TARGET ${target_name} POST_BUILD
COMMAND ${CMAKE_STRIP} -x $<TARGET_FILE:${target_name}>) COMMAND ${CMAKE_STRIP} -x $<TARGET_FILE:${target_name}>)
else() else()
add_custom_command(TARGET ${target_name} POST_BUILD add_custom_command(TARGET ${target_name} POST_BUILD
COMMAND ${CMAKE_STRIP} $<TARGET_FILE:${target_name}>) COMMAND ${CMAKE_STRIP} $<TARGET_FILE:${target_name}>)
endif()
endif() endif()
endif() endif()
elseif(MSVC) endif()
if(MSVC)
# /MP enables multithreaded builds (relevant when there are many files), /bigobj is # /MP enables multithreaded builds (relevant when there are many files), /bigobj is
# needed for bigger binding projects due to the limit to 64k addressable sections # needed for bigger binding projects due to the limit to 64k addressable sections
target_compile_options(${target_name} PRIVATE /MP /bigobj) target_compile_options(${target_name} PRIVATE /MP /bigobj)
# Enforce link time code generation on MSVC, except in debug mode
target_compile_options(${target_name} PRIVATE $<$<NOT:$<CONFIG:Debug>>:/GL>)
# Fancy generator expressions don't work with linker flags, for reasons unknown
set_property(TARGET ${target_name} APPEND_STRING PROPERTY LINK_FLAGS_RELEASE /LTCG)
set_property(TARGET ${target_name} APPEND_STRING PROPERTY LINK_FLAGS_MINSIZEREL /LTCG)
set_property(TARGET ${target_name} APPEND_STRING PROPERTY LINK_FLAGS_RELWITHDEBINFO /LTCG)
endif() endif()
endfunction() endfunction()