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[CMake] Add support for link time optimization (LTO).

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This analogous to the `--optimize` flag in the Python/Makefile
build system except that we now support doing LTO with Clang/GCC
as well. However it is probably best to avoid doing LTO with
Clang or GCC for now because I see a bunch of warnings about
ODR violations when building with LTO.

LTO can be enabled with the new `LINK_TIME_OPTIMIZATION` option
which is off by default.
This commit is contained in:
Dan Liew 2017-04-29 01:21:49 +01:00
parent fb403229bd
commit 0e1343e78d
3 changed files with 58 additions and 0 deletions
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52
contrib/cmake/cmake/compiler_lto.cmake Normal file
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option(LINK_TIME_OPTIMIZATION "Use link time optimiziation" OFF)
if (LINK_TIME_OPTIMIZATION)
message(STATUS "LTO enabled")
set(build_types_with_lto "RELEASE" "RELWITHDEBINFO")
if (DEFINED CMAKE_CONFIGURATION_TYPES)
# Multi configuration generator
message(STATUS "Note LTO is only enabled for the following configurations: ${build_types_with_lto}")
else()
# Single configuration generator
string(TOUPPER "${CMAKE_BUILD_TYPE}" _build_type_upper)
list(FIND build_types_with_lto "${_build_type_upper}" _index)
if ("${_index}" EQUAL -1)
message(FATAL_ERROR "Configuration ${CMAKE_BUILD_TYPE} does not support LTO."
"You should set LINK_TIME_OPTIMIZATION to OFF.")
endif()
endif()
set(_lto_compiler_flag "")
set(_lto_linker_flag "")
if (("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang") OR
("${CMAKE_CXX_COMPILER_ID}" MATCHES "GNU"))
set(_lto_compiler_flag "-flto")
set(_lto_linker_flag "-flto")
# FIXME: Remove "x.." when CMP0054 is set to NEW
elseif ("x${CMAKE_CXX_COMPILER_ID}" STREQUAL "xMSVC")
set(_lto_compiler_flag "/GL")
set(_lto_linker_flag "/LTCG")
else()
message(FATAL_ERROR "Can't enable LTO for compiler \"${CMAKE_CXX_COMPILER_ID}\"."
"You should set LINK_TIME_OPTIMIZATION to OFF.")
endif()
CHECK_CXX_COMPILER_FLAG("${_lto_compiler_flag}" HAS_LTO)
if (NOT HAS_LTO)
message(FATAL_ERROR "Compiler does not support LTO")
endif()
foreach (_config ${build_types_with_lto})
# Set flags compiler and linker flags globally rather than using
# `Z3_COMPONENT_CXX_FLAGS` and `Z3_DEPENDENT_EXTRA_CXX_LINK_FLAGS`
# respectively. We need per configuration compiler and linker flags. The
# `LINK_FLAGS` property (which we populate with
# `Z3_DEPENDENT_EXTRA_CXX_LINK_FLAGS`) doesn't seem to support generator
# expressions so we can't do `$<$<CONFIG:Release>:${_lto_linker_flag}>`.
set(CMAKE_CXX_FLAGS_${_config} "${CMAKE_CXX_FLAGS_${_config}} ${_lto_compiler_flag}")
set(CMAKE_EXE_LINKER_FLAGS_${_config} "${CMAKE_EXE_LINKER_FLAGS_${_config}} ${_lto_linker_flag}")
set(CMAKE_SHARED_LINKER_FLAGS_${_config} "${CMAKE_SHARED_LINKER_FLAGS_${_config}} ${_lto_linker_flag}")
set(CMAKE_STATIC_LINKER_FLAGS_${_config} "${CMAKE_STATIC_LINKER_FLAGS_${_config}} ${_lto_linker_flag}")
endforeach()
else()
message(STATUS "LTO disabled")
endif()