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Add new option to build p4c with LTO #3470

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Sep 3, 2022
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Add new option to build p4c with LTO #3470

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5863bc2
Add new option to build p4c with LTO
davidbolvansky Aug 1, 2022
fa2918d
Warn if GCC used with LLD, switch to Gold
davidbolvansky Aug 1, 2022
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15 changes: 15 additions & 0 deletions CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -40,6 +40,7 @@ OPTION (ENABLE_PROTOBUF_STATIC "Link against Protobuf statically" ON)
OPTION (ENABLE_GC "Use libgc" ON)
OPTION (ENABLE_MULTITHREAD "Use multithreading" OFF)
OPTION (ENABLE_GMP "Use GMP library" ON)
OPTION (ENABLE_LTO "Enable Link Time Optimization (LTO)" OFF)
OPTION (BUILD_STATIC_RELEASE "Build a statically linked release binary" OFF)

set (P4C_DRIVER_NAME "p4c" CACHE STRING "Customize the name of the driver script")
Expand Down Expand Up @@ -220,10 +221,24 @@ add_cxx_compiler_option ("-Wno-deprecated-declarations")
# If we're on GCC or Clang, use the prefer LLD or Gold linker if available.
set(BUILD_LINK_WITH_GOLD ON CACHE BOOL "Use Gold linker for build if available")
set(BUILD_LINK_WITH_LLD ON CACHE BOOL "Use LLD linker for build if available (overrides BUILD_LINK_WITH_GOLD)")

# Build with LTO
if (ENABLE_LTO AND CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
if (BUILD_LINK_WITH_LLD)
message(WARNING "LLD does not work with GCC's LTO object format, switching to Gold.")
set(BUILD_LINK_WITH_LLD OFF)
endif ()
add_cxx_compiler_option ("-flto")
endif ()

if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU" OR CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
# We want to optimize the binary size for a static release binary.
# This only works with modern versions of GCC.
if (BUILD_STATIC_RELEASE AND CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER 8.0)
if (BUILD_LINK_WITH_LLD)
message(WARNING "LLD does not work with GCC's LTO object format, switching to Gold.")
set(BUILD_LINK_WITH_LLD OFF)
endif ()
add_cxx_compiler_option ("-flto")
endif ()
set(_LD_USED "default system")
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3 changes: 3 additions & 0 deletions README.md
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Expand Up @@ -194,6 +194,9 @@ sudo dpkg -i /path/to/package.deb
- `-DENABLE_MULTITHREAD=ON|OFF`. Use multithreading. Default is
OFF.
- `-DENABLE_GMP=ON|OFF`. Use the GMP library. Default is ON.
- `-DBUILD_LINK_WITH_GOLD=ON|OFF`. Use Gold linker for build if available.
- `-DBUILD_LINK_WITH_LLD=ON|OFF`. Use LLD linker for build if available (overrides BUILD_LINK_WITH_GOLD).
- `-DENABLE_LTO=ON|OFF`. Use Link Time Optimization (LTO). Default is OFF.

If adding new targets to this build system, please see
[instructions](#defining-new-cmake-targets).
Expand Down