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[CMake] Fix MSVC runtime selection and add official Release cache #8804

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[CMake] Fix MSVC runtime selection and add official Release cache #8804

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1a7e305
[CMake] Fix MSVC runtime library selection
alsepkow Aug 19, 2026
1d4b357
[CMake] Add official Release cache
alsepkow Aug 20, 2026
fa02b21
[Docs] Defer official Release build guidance
alsepkow Aug 20, 2026
4c7b117
[CMake] Clarify legacy CRT flag detection
alsepkow Aug 20, 2026
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6 changes: 6 additions & 0 deletions cmake/caches/OfficialRelease.cmake
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Original file line number Diff line number Diff line change
@@ -0,0 +1,6 @@
# Settings used to build official DXC Release binaries.

include("${CMAKE_CURRENT_LIST_DIR}/PredefinedParams.cmake")

set(LLVM_USE_CRT_RELEASE MT CACHE STRING
"Use the static multithreaded MSVC runtime for Release builds.")
78 changes: 41 additions & 37 deletions cmake/modules/ChooseMSVCCRT.cmake
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Original file line number Diff line number Diff line change
Expand Up @@ -4,15 +4,11 @@
#
# The macro is invoked at the end of the file.
#
# CMake already sets CRT flags in the CMAKE_CXX_FLAGS_* and
# CMAKE_C_FLAGS_* variables by default. To let the user
# override that for each build type:
# 1. Detect which CRT is already selected, and reflect this in
# LLVM_USE_CRT_* so the user can have a better idea of what
# changes they're making.
# 2. Replace the flags in both variables with the new flag via a regex.
# 3. set() the variables back into the cache so the changes
# are user-visible.
# To let the user override the MSVC runtime library for each build type:
# 1. Detect legacy /MD, /MDd, /MT, and /MTd switches in the
# CMAKE_<LANG>_FLAGS_<CONFIG> variables and reflect them in LLVM_USE_CRT_*.
# 2. Validate explicitly selected LLVM_USE_CRT_* values.
# 3. Translate them to CMake's MSVC runtime library abstraction.

### Helper macros: ###
macro(make_crt_regex regex crts)
Expand All @@ -33,24 +29,6 @@ macro(get_current_crt crt_current regex flagsvar)
string(STRIP "${${crt_current}}" ${crt_current})
endmacro(get_current_crt)

# Replaces or adds a flag to a variable.
# Expects 'flag' to be padded with spaces.
macro(set_flag_in_var flagsvar regex flag)
string(REGEX MATCH "${${regex}}" current_flag "${${flagsvar}}")
if("${current_flag}" STREQUAL "")
set(${flagsvar} "${${flagsvar}}${${flag}}")
else()
string(REGEX REPLACE "${${regex}}" "${${flag}}" ${flagsvar} "${${flagsvar}}")
endif()
string(STRIP "${${flagsvar}}" ${flagsvar})
# Make sure this change gets reflected in the cache/gui.
# CMake requires the docstring parameter whenever set() touches the cache,
# so get the existing docstring and re-use that.
get_property(flagsvar_docs CACHE ${flagsvar} PROPERTY HELPSTRING)
set(${flagsvar} "${${flagsvar}}" CACHE STRING "${flagsvar_docs}" FORCE)
endmacro(set_flag_in_var)


macro(choose_msvc_crt MSVC_CRT)
if(LLVM_USE_CRT)
message(FATAL_ERROR
Expand All @@ -60,7 +38,10 @@ variables (LLVM_USE_CRT_DEBUG, etc) instead.")

make_crt_regex(MSVC_CRT_REGEX ${MSVC_CRT})

foreach(build_type ${CMAKE_CONFIGURATION_TYPES} ${CMAKE_BUILD_TYPE})
set(llvm_crt_build_types ${CMAKE_CONFIGURATION_TYPES} ${CMAKE_BUILD_TYPE})
list(REMOVE_DUPLICATES llvm_crt_build_types)

foreach(build_type ${llvm_crt_build_types})
string(TOUPPER "${build_type}" build)
if (NOT LLVM_USE_CRT_${build})
get_current_crt(LLVM_USE_CRT_${build}
Expand All @@ -75,23 +56,47 @@ variables (LLVM_USE_CRT_DEBUG, etc) instead.")
endif(NOT LLVM_USE_CRT_${build})
endforeach(build_type)

foreach(build_type ${CMAKE_CONFIGURATION_TYPES} ${CMAKE_BUILD_TYPE})
set(llvm_crt_override_requested FALSE)
foreach(build_type ${llvm_crt_build_types})
string(TOUPPER "${build_type}" build)
if ("${LLVM_USE_CRT_${build}}" STREQUAL "")
set(flag_string " ")
else()
set(flag_string " /${LLVM_USE_CRT_${build}} ")
if (NOT "${LLVM_USE_CRT_${build}}" STREQUAL "")
set(llvm_crt_override_requested TRUE)
list(FIND ${MSVC_CRT} ${LLVM_USE_CRT_${build}} idx)
if (idx LESS 0)
message(FATAL_ERROR
"Invalid value for LLVM_USE_CRT_${build}: ${LLVM_USE_CRT_${build}}. Valid options are one of: ${${MSVC_CRT}}")
endif (idx LESS 0)
message(STATUS "Using ${build_type} VC++ CRT: ${LLVM_USE_CRT_${build}}")
endif()
foreach(lang C CXX)
set_flag_in_var(CMAKE_${lang}_FLAGS_${build} MSVC_CRT_REGEX flag_string)
endforeach(lang)
endforeach(build_type)

if (llvm_crt_override_requested)
set(cmake_msvc_runtime_library "")
foreach(build_type ${llvm_crt_build_types})
string(TOUPPER "${build_type}" build)
set(crt "${LLVM_USE_CRT_${build}}")
if ("${crt}" STREQUAL "")
if ("${build}" STREQUAL "DEBUG")
set(crt "MDd")
else()
set(crt "MD")
endif()
endif()

if ("${crt}" STREQUAL "MD")
set(runtime_library "MultiThreadedDLL")
elseif ("${crt}" STREQUAL "MDd")
set(runtime_library "MultiThreadedDebugDLL")
elseif ("${crt}" STREQUAL "MT")
set(runtime_library "MultiThreaded")
elseif ("${crt}" STREQUAL "MTd")
set(runtime_library "MultiThreadedDebug")
endif()
string(APPEND cmake_msvc_runtime_library
"$<$<CONFIG:${build_type}>:${runtime_library}>")
endforeach(build_type)
set(CMAKE_MSVC_RUNTIME_LIBRARY "${cmake_msvc_runtime_library}")
endif()
endmacro(choose_msvc_crt MSVC_CRT)


Expand All @@ -103,4 +108,3 @@ set(MSVC_CRT
MTd)

choose_msvc_crt(MSVC_CRT)

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