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Make Whole Program Optimization (WPO) optional on MSVC (backport #532) #536

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Make Whole Program Optimization (WPO) optional on MSVC (backport #532) #536

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39 changes: 28 additions & 11 deletions cmake/IgnSetCompilerFlags.cmake
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Original file line number Diff line number Diff line change
Expand Up @@ -294,23 +294,35 @@ macro(ign_setup_msvc)
# W2: Warning level 2: significant warnings.
# TODO: Recommend Wall in the future.
# Note: MSVC /Wall generates tons of warnings on gtest code.
set(MSVC_MINIMAL_FLAGS "/Gy /W2")
# bigobj: Increase the number of sections in an object file, which is often needed
# for complex templated code or when using Whole Program Optimization (/GL).
set(MSVC_MINIMAL_FLAGS "/Gy /W2 /bigobj")

# Zi: Produce complete debug information
# Note: We provide Zi to ordinary release mode because it does not impact
# performance and can be helpful for debugging.
set(MSVC_DEBUG_FLAGS "${MSVC_MINIMAL_FLAGS} /Zi")

# GL: Enable Whole Program Optimization
set(MSVC_RELEASE_FLAGS "${MSVC_DEBUG_FLAGS} /GL")

# UNDEBUG: Undefine NDEBUG so that assertions can be triggered
set(MSVC_RELWITHDEBINFO_FLAGS "${MSVC_RELEASE_FLAGS} /UNDEBUG")

# INCREMENTAL:NO fix LNK4075 warning
# LTCG: need when using /GL above
# see https://docs.microsoft.com/en-us/cpp/build/reference/gl-whole-program-optimization
set(MSVC_RELWITHDEBINFO_LINKER_FLAGS "/INCREMENTAL:NO /LTCG")
option(GZ_MSVC_WPO "Enable Whole Program Optimization on MSVC" ON)
if(GZ_MSVC_WPO)
# GL: Enable Whole Program Optimization
set(MSVC_RELEASE_FLAGS "${MSVC_DEBUG_FLAGS} /GL")

# UNDEBUG: Undefine NDEBUG so that assertions can be triggered
set(MSVC_RELWITHDEBINFO_FLAGS "${MSVC_RELEASE_FLAGS} /UNDEBUG")
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@azeey azeey Mar 25, 2026

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Same comment as #533 (comment). @j-rivero mind taking a look?


# LTCG: need when using /GL above
set(MSVC_RELEASE_LINKER_FLAGS "/LTCG")

# INCREMENTAL:NO fix LNK4075 warning
# see https://docs.microsoft.com/en-us/cpp/build/reference/gl-whole-program-optimization
set(MSVC_RELWITHDEBINFO_LINKER_FLAGS "/INCREMENTAL:NO /LTCG")
else()
set(MSVC_RELEASE_FLAGS "${MSVC_DEBUG_FLAGS}")
set(MSVC_RELWITHDEBINFO_FLAGS "${MSVC_RELEASE_FLAGS} /UNDEBUG")
set(MSVC_RELEASE_LINKER_FLAGS "")
set(MSVC_RELWITHDEBINFO_LINKER_FLAGS "/INCREMENTAL:NO")
endif()

# cmake automatically provides /Zi /Ob0 /Od /RTC1
set(CMAKE_C_FLAGS_DEBUG "${CMAKE_C_FLAGS_DEBUG} ${MSVC_DEBUG_FLAGS}")
Expand All @@ -319,11 +331,16 @@ macro(ign_setup_msvc)
# cmake automatically provides /O2 /Ob2 /DNDEBUG
set(CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS_RELEASE} ${MSVC_RELEASE_FLAGS}")
set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} ${MSVC_RELEASE_FLAGS}")
set(CMAKE_SHARED_LINKER_FLAGS_RELEASE "${CMAKE_SHARED_LINKER_FLAGS_RELEASE} ${MSVC_RELEASE_LINKER_FLAGS}")
set(CMAKE_EXE_LINKER_FLAGS_RELEASE "${CMAKE_EXE_LINKER_FLAGS_RELEASE} ${MSVC_RELEASE_LINKER_FLAGS}")
set(CMAKE_STATIC_LINKER_FLAGS_RELEASE "${CMAKE_STATIC_LINKER_FLAGS_RELEASE} ${MSVC_RELEASE_LINKER_FLAGS}")

# cmake automatically provides /Zi /O2 /Ob1 /DNDEBUG
set(CMAKE_C_FLAGS_RELWITHDEBINFO "${CMAKE_C_FLAGS_RELWITHDEBINFO} ${MSVC_RELWITHDEBINFO_FLAGS}")
set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "${CMAKE_CXX_FLAGS_RELWITHDEBINFO} ${MSVC_RELWITHDEBINFO_FLAGS}")
set(CMAKE_SHARED_LINKER_FLAGS_RELWITHDEBINFO "${CMAKE_SHARED_LINKER_FLAGS_RELWITHDEBINFO} ${MSVC_RELWITHDEBINFO_LINKER_FLAGS}")
set(CMAKE_EXE_LINKER_FLAGS_RELWITHDEBINFO "${CMAKE_EXE_LINKER_FLAGS_RELWITHDEBINFO} ${MSVC_RELWITHDEBINFO_LINKER_FLAGS}")
set(CMAKE_STATIC_LINKER_FLAGS_RELWITHDEBINFO "${CMAKE_STATIC_LINKER_FLAGS_RELWITHDEBINFO} ${MSVC_RELWITHDEBINFO_LINKER_FLAGS}")

# cmake automatically provides /O1 /Ob1 /DNDEBUG
set(CMAKE_C_FLAGS_MINSIZEREL "${CMAKE_C_FLAGS_MINSIZEREL} ${MSVC_MINIMAL_FLAGS}")
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