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module-template: fix the IPO check, and default IPO off #11

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Merged
siahisaforker merged 1 commit into from
Aug 10, 2026
Merged

module-template: fix the IPO check, and default IPO off #11

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26 changes: 25 additions & 1 deletion module-template/CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -120,7 +120,17 @@ if(UNIX AND NOT APPLE)
"${CMAKE_CURRENT_SOURCE_DIR}/module.exports")
endif()

option(RECOMPCORE_MODULE_ENABLE_IPO "Enable Clang module interprocedural optimization when supported" ON)
# Off by default because it was measured and it did not pay. On MKDD/arm64,
# same PGO profile, only -flto=thin differing, alternating A/B on one scene:
# 1.1826 without against 1.1733 with, i.e. -0.8% with overlapping ranges. It
# also makes the link markedly slower. Turn it on with -D...=ON to re-measure.
#
# It was ON here for a long time and did nothing on macOS anyway: the support
# check below could not pass. See the comment on it. Anyone who was getting IPO
# before -- Linux builds, where GNU ar makes the check succeed -- loses it with
# this default, which is a deliberate choice and not a measured one on that
# platform.
option(RECOMPCORE_MODULE_ENABLE_IPO "Enable Clang module interprocedural optimization when supported" OFF)
set(RECOMPCORE_MODULE_OPT_LEVEL "2" CACHE STRING
"Optimization level for generated module translation units (0, 1, 2, or 3)")
set_property(CACHE RECOMPCORE_MODULE_OPT_LEVEL PROPERTY STRINGS 0 1 2 3)
Expand All @@ -130,8 +140,22 @@ if(NOT RECOMPCORE_MODULE_OPT_LEVEL MATCHES "^[0-3]$")
endif()
if(RECOMPCORE_MODULE_ENABLE_IPO AND CMAKE_C_COMPILER_ID MATCHES "Clang")
include(CheckIPOSupported)
# moderngekko-port configures with CMAKE_NINJA_FORCE_RESPONSE_FILE=1, which the
# module needs: it links thousands of chunk objects and the command line does
# not fit in ARG_MAX. But check_ipo_supported's try-compile inherits the
# environment, and its static-library step then runs `ar qc libfoo.a @foo.rsp`
# -- Apple's /usr/bin/ar has no @file support, so the check fails with
# "ar: @CMakeFiles/foo.rsp: No such file or directory" and IPO is silently
# disabled. The manifest still records -flto=thin. Every module built this way
# had NO cross-translation-unit inlining. Scope the variable off for the check
# only, then restore it before the generator reads it.
set(_module_forced_rsp "$ENV{CMAKE_NINJA_FORCE_RESPONSE_FILE}")
unset(ENV{CMAKE_NINJA_FORCE_RESPONSE_FILE})
check_ipo_supported(RESULT RECOMPCORE_MODULE_IPO_SUPPORTED
OUTPUT RECOMPCORE_MODULE_IPO_ERROR LANGUAGES C)
if(_module_forced_rsp)
set(ENV{CMAKE_NINJA_FORCE_RESPONSE_FILE} "${_module_forced_rsp}")
endif()
if(RECOMPCORE_MODULE_IPO_SUPPORTED)
set_property(TARGET ${MODULE_NAME} PROPERTY INTERPROCEDURAL_OPTIMIZATION TRUE)
else()
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