Merge pull request #9254 from The-OpenROAD-Project-staging/secure-enable-lto

Enabled LTO (Link Time Optimization)

Author: maliberty

.bazelrc

@@ -16,6 +16,14 @@ build --cxxopt "-std=c++20"        --host_cxxopt "-std=c++20"
 build --cxxopt "-xc++"             --host_cxxopt "-xc++"
 build --cxxopt "-DBAZEL_BUILD"     --host_cxxopt "-DBAZEL_BUILD"
 
+# Default to optimized build (-c opt), O3
+build -c opt
+build:opt --copt=-O3
+
+# Enable Full-LTO (Link Time Optimization)
+build:opt --copt=-flto
+build:opt --linkopt=-flto
+
 # Needed for floating point stability in FFT (fft_test will check this).
 # See also https://kristerw.github.io/2021/11/09/fp-contract/
 build --cxxopt "-ffp-contract=off" --host_cxxopt "-ffp-contract=off"

CMakeLists.txt

@@ -108,6 +108,51 @@ message(STATUS "C++ Standard: ${CMAKE_CXX_STANDARD}")
 message(STATUS "C++ Standard Required: ${CMAKE_CXX_STANDARD_REQUIRED}")
 message(STATUS "C++ Extensions: ${CMAKE_CXX_EXTENSIONS}")
 
+# Detect OS distribution and version from /etc/os-release
+# LTO is known to cause build errors on Debian 11 and Rocky Linux 8
+set(LTO_UNSUPPORTED_OS FALSE)
+if(EXISTS "/etc/os-release")
+  file(STRINGS "/etc/os-release" OS_RELEASE_CONTENTS)
+  set(OS_ID "")
+  set(OS_VERSION_ID "")
+  foreach(line ${OS_RELEASE_CONTENTS})
+    if(line MATCHES "^ID=(.*)$")
+      string(REGEX REPLACE "^ID=\"?([^\"]*)\"?$" "\\1" OS_ID "${line}")
+    endif()
+    if(line MATCHES "^VERSION_ID=(.*)$")
+      string(REGEX REPLACE "^VERSION_ID=\"?([^\"]*)\"?$" "\\1" OS_VERSION_ID "${line}")
+    endif()
+  endforeach()
+
+  # Check for unsupported OS for LTO
+  if((OS_ID STREQUAL "debian" AND OS_VERSION_ID STREQUAL "11") OR
+     (OS_ID STREQUAL "rocky" AND OS_VERSION_ID MATCHES "^8"))
+    set(LTO_UNSUPPORTED_OS TRUE)
+    message(STATUS "Detected unsupported OS (${OS_ID} ${OS_VERSION_ID}): LTO will be disabled due to known build issues")
+  endif()
+endif()
+
+option(LINK_TIME_OPTIMIZATION "Flag to control link time optimization: on by default" ON)
+set(LTO_STATUS "disabled")
+if (LINK_TIME_OPTIMIZATION AND NOT LTO_UNSUPPORTED_OS)
+  include(CheckIPOSupported)
+  check_ipo_supported(RESULT lto_supported OUTPUT lto_error)
+  if(lto_supported)
+    # LTO is enabled globally for Release build
+    set(CMAKE_INTERPROCEDURAL_OPTIMIZATION_RELEASE TRUE)
+    set(CMAKE_INTERPROCEDURAL_OPTIMIZATION_RELWITHDEBINFO FALSE)
+    set(CMAKE_INTERPROCEDURAL_OPTIMIZATION_DEBUG FALSE)
+
+    string(TOUPPER "${CMAKE_BUILD_TYPE}" UPPER_BUILD_TYPE)
+    if(UPPER_BUILD_TYPE STREQUAL "RELEASE")
+      set(LTO_STATUS "enabled")
+    endif()
+  else()
+    set(LTO_STATUS "not supported: ${lto_error}")
+  endif()
+endif()
+message(STATUS "LTO/IPO is ${LTO_STATUS}")
+
 # configure a header file to pass some of the CMake settings
 configure_file(
   ${OPENROAD_HOME}/include/ord/Version.hh.cmake

src/gui/CMakeLists.txt

@@ -86,6 +86,14 @@ if (Qt5_FOUND AND BUILD_GUI)
       OpenSTA
   )
 
+  # Disable LTO for gui. LTO causes a crash with Qt plugin loading
+  set_target_properties(gui PROPERTIES 
+    INTERPROCEDURAL_OPTIMIZATION OFF
+    INTERPROCEDURAL_OPTIMIZATION_RELEASE OFF
+  )
+  target_compile_options(gui PRIVATE "-fno-lto")
+  target_link_options(gui PRIVATE "-fno-lto")
+
 messages(
   TARGET gui
 )