root-project · guitargeek · Dec 18, 2025 · Dec 17, 2025 · Dec 19, 2025 · Dec 19, 2025
@@ -6,7 +6,7 @@ set -ex
 mkdir ../build
 cd ../build
 cmake -DCMAKE_EXPORT_COMPILE_COMMANDS=ON -Dall=On -Dtesting=On -Dx11=Off -Dalien=Off \
-      -Dcuda=Off -Dtmva-gpu=Off -Dveccore=Off ../root
+      -Dcuda=Off -Dtmva-gpu=Off ../root
 # We need to prebuild a minimal set of targets which are responsible for header copy
 # or generation.
 make -j4 move_headers intrinsics_gen clang-tablegen-targets ClangDriverOptions \

@@ -24,9 +24,7 @@ builtin_openui5=ON
 builtin_pcre=OFF
 builtin_tbb=OFF
 builtin_unuran=OFF
-builtin_vc=OFF
 builtin_vdt=OFF
-builtin_veccore=OFF
 builtin_xrootd=OFF
 builtin_xxhash=OFF
 builtin_zeromq=ON
@@ -97,9 +95,7 @@ tmva=ON
 unfold=ON
 unuran=ON
 uring=OFF
-vc=OFF
 vdt=ON
-veccore=OFF
 vecgeom=OFF
 webgui=ON
 win_broken_tests=OFF

@@ -17,7 +17,6 @@ builtin_pcre=ON
 builtin_tbb=ON
 builtin_unuran=ON
 builtin_vdt=ON
-builtin_veccore=ON
 builtin_xrootd=ON
 builtin_xxhash=ON
 builtin_zeromq=ON

@@ -18,9 +18,7 @@ builtin_openssl=ON
 builtin_pcre=ON
 builtin_tbb=ON
 builtin_unuran=ON
-builtin_vc=ON
 builtin_vdt=ON
-builtin_veccore=ON
 builtin_xrootd=ON
 builtin_xxhash=ON
 builtin_zeromq=ON

@@ -16,7 +16,6 @@ builtin_pcre=ON
 builtin_tbb=ON
 builtin_unuran=ON
 builtin_vdt=ON
-builtin_veccore=ON
 builtin_xrootd=ON
 builtin_xxhash=ON
 builtin_zeromq=ON

@@ -17,7 +17,6 @@ builtin_pcre=ON
 builtin_tbb=ON
 builtin_unuran=ON
 builtin_vdt=ON
-builtin_veccore=ON
 builtin_xrootd=ON
 builtin_xxhash=ON
 builtin_zeromq=ON

@@ -71,6 +71,20 @@ This change affects the following classes:  `TFile`, `TMapFile`, `TMemFile`, `TD
 
 ## Math
 
+### Migration from Vc to `std::simd`
+
+ROOT has migrated its internal SIMD usage from **Vc** to `std::simd` where applicable.
+
+This change affects:
+  * The vectorized backend of **TFormula** and **TMath** interfaces that are available via VecCore when building ROOT with `veccore=ON`.
+  * Users who instantiate the GenVector classes with Vc SIMD types like `Vc::double_v`. If you rely on these types, your code must be update to use `std::simd` instead.
+
+* On **Windows and Apple silicon platforms**, this change has no practical impact: Vc-based SIMD via VecCore was not supported by ROOT on these platforms, and ROOT will also not try to use `std::simd` now on these platforms.
+
+* TFormula and TMath attempt to use `std::simd` when compiled with **Clang** (any supported version) or **GCC ≥ 9**. On other compilers or configurations, SIMD support is disabled. This affects in particular the default compiler on RHEL/AlmaLinux 8 (GCC 8.5).
+
+* As a consequence of this migration, the build options **vc** and **builtin_vc** are now deprecated and ignored. Their usage will cause CMake configuration errors starting from ROOT 6.42.
+
 ## RooFit
 
 ## RDataFrame

@@ -107,9 +107,7 @@ ROOT_BUILD_OPTION(builtin_pcre OFF "Build bundled copy of PCRE")
 ROOT_BUILD_OPTION(builtin_png OFF "Build bundled copy of libpng")
 ROOT_BUILD_OPTION(builtin_tbb OFF "Build TBB internally (requires network)")
 ROOT_BUILD_OPTION(builtin_unuran OFF "Build bundled copy of unuran")
-ROOT_BUILD_OPTION(builtin_vc OFF "Build Vc internally (requires network)")
 ROOT_BUILD_OPTION(builtin_vdt OFF "Build VDT internally (requires network)")
-ROOT_BUILD_OPTION(builtin_veccore OFF "Build VecCore internally (requires network)")
 ROOT_BUILD_OPTION(builtin_xrootd OFF "Build XRootD internally (requires network)")
 ROOT_BUILD_OPTION(builtin_xxhash OFF "Build bundled copy of xxHash")
 ROOT_BUILD_OPTION(builtin_zeromq OFF "Build ZeroMQ internally (requires network)")
@@ -180,9 +178,7 @@ ROOT_BUILD_OPTION(unfold OFF "Enable the unfold package [GPL]")
 ROOT_BUILD_OPTION(unuran OFF "Enable support for UNURAN (package for generating non-uniform random numbers) [GPL]")
 ROOT_BUILD_OPTION(uring OFF "Enable support for io_uring (requires liburing and Linux kernel >= 5.1)")
 ROOT_BUILD_OPTION(use_gsl_cblas ON "Use the CBLAS library from GSL instead of finding a more optimized BLAS library automatically with FindBLAS (the GSL CBLAS is less performant but more portable)")
-ROOT_BUILD_OPTION(vc OFF "Enable support for Vc (SIMD Vector Classes for C++)")
 ROOT_BUILD_OPTION(vdt ON "Enable support for VDT (fast and vectorisable mathematical functions)")
-ROOT_BUILD_OPTION(veccore OFF "Enable support for VecCore SIMD abstraction library")
 ROOT_BUILD_OPTION(vecgeom OFF "Enable support for VecGeom vectorized geometry library")
 ROOT_BUILD_OPTION(webgui ON "Build Web-based UI components of ROOT")
 ROOT_BUILD_OPTION(win_broken_tests OFF "Enable broken tests on Windows")
@@ -253,9 +249,7 @@ if(all)
  set(tmva-pymva_defvalue ON)
  set(tmva-rmva_defvalue ON)
  set(unuran_defvalue ON)
- set(vc_defvalue ON)
  set(vdt_defvalue ON)
- set(veccore_defvalue ON)
  set(vecgeom_defvalue ON)
  set(x11_defvalue ON)
  set(xml_defvalue ON)
@@ -295,9 +289,7 @@ if(builtin_all)
   set(builtin_png_defvalue ON)
   set(builtin_tbb_defvalue ON)
 #  set(builtin_unuran_defvalue ON) (GPL)
-  set(builtin_vc_defvalue ON)
   set(builtin_vdt_defvalue ON)
-  set(builtin_veccore_defvalue ON)
   set(builtin_xrootd_defvalue ON)
   set(builtin_xxhash_defvalue ON)
   set(builtin_zeromq_defvalue ON)
@@ -415,6 +407,14 @@ if(DEFINED rpath)
       "") # empty line at the end to make the deprecation message more visible
 endif()
 
+foreach(opt vc builtin_vc veccore builtin_veccore)
+  if(${opt})
+    message(DEPRECATION ">>> Option '${opt}' is deprecated and ignored."
+        "ROOT now uses std::experimental::simd for the vectorized TFormula and TMath classes when available (on Linux when compiling with C++20 or higher)."
+        "Using this option will result in configuration errors in ROOT 6.42.")
+  endif()
+endforeach()
+
 foreach(opt minuit2_mpi)
   if(${opt})
       message(WARNING "The option '${opt}' can only be used to minimise thread-safe functions in Minuit2. It cannot be used for Histogram/Graph fitting and for RooFit. If you want to use Minuit2 with MPI support, it is better to build Minuit2 as a standalone library.")

@@ -365,20 +365,16 @@ if(cocoa)
 else()
   set(hascocoa undef)
 endif()
-if(vc)
-  set(hasvc define)
-else()
-  set(hasvc undef)
-endif()
 if(vdt)
   set(hasvdt define)
 else()
   set(hasvdt undef)
 endif()
-if(veccore)
-  set(hasveccore define)
+# Assume std::experimental::simd is available on Linux if we build with C++20 on Linux
+if(WIN32 OR APPLE OR CMAKE_CXX_STANDARD LESS 20)
+  set(hasstdsimd undef)
 else()
-  set(hasveccore undef)
+  set(hasstdsimd define)
 endif()
 if(dataframe)
   set(hasdataframe define)

@@ -1365,194 +1365,6 @@ if(builtin_tbb)
   set(TBB_TARGET TBB)
 endif()
 
-#---Check for Vc---------------------------------------------------------------------
-if(builtin_vc)
-  unset(Vc_FOUND)
-  unset(Vc_FOUND CACHE)
-  set(vc ON CACHE BOOL "Enabled because builtin_vc requested (${vc_description})" FORCE)
-elseif(vc)
-  if(fail-on-missing)
-    find_package(Vc 1.4.4 CONFIG QUIET REQUIRED)
-  else()
-    find_package(Vc 1.4.4 CONFIG QUIET)
-    if(NOT Vc_FOUND)
-      message(STATUS "Vc library not found, support for it disabled.")
-      message(STATUS "Please enable the option 'builtin_vc' to build Vc internally.")
-      set(vc OFF CACHE BOOL "Disabled because Vc not found (${vc_description})" FORCE)
-    endif()
-  endif()
-  if(Vc_FOUND)
-    set_property(DIRECTORY APPEND PROPERTY INCLUDE_DIRECTORIES ${Vc_INCLUDE_DIR})
-    BUILD_ROOT_INCLUDE_PATH("${Vc_INCLUDE_DIR}")
-  endif()
-endif()
-
-if(vc AND NOT Vc_FOUND)
-  ROOT_CHECK_CONNECTION_AND_DISABLE_OPTION("vc")
-endif()
-
-if(vc AND NOT Vc_FOUND)
-  set(Vc_VERSION "1.4.4")
-  set(Vc_PROJECT "Vc-${Vc_VERSION}")
-  set(Vc_SRC_URI "${lcgpackages}/${Vc_PROJECT}.tar.gz")
-  set(Vc_DESTDIR "${CMAKE_BINARY_DIR}/externals")
-  set(Vc_ROOTDIR "${Vc_DESTDIR}/${CMAKE_INSTALL_PREFIX}")
-  set(Vc_LIBNAME "${CMAKE_STATIC_LIBRARY_PREFIX}Vc${CMAKE_STATIC_LIBRARY_SUFFIX}")
-  set(Vc_LIBRARY "${Vc_ROOTDIR}/lib/${Vc_LIBNAME}")
-
-  ExternalProject_Add(VC
-    URL     ${Vc_SRC_URI}
-    URL_HASH SHA256=5933108196be44c41613884cd56305df320263981fe6a49e648aebb3354d57f3
-    BUILD_IN_SOURCE 0
-    BUILD_BYPRODUCTS ${Vc_LIBRARY}
-    LOG_DOWNLOAD 1 LOG_CONFIGURE 1 LOG_BUILD 1 LOG_INSTALL 1 LOG_OUTPUT_ON_FAILURE 1
-    CMAKE_ARGS -G ${CMAKE_GENERATOR}
-               -DCMAKE_POLICY_VERSION_MINIMUM=3.5
-               -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}
-               -DCMAKE_C_COMPILER=${CMAKE_C_COMPILER}
-               -DCMAKE_C_FLAGS=${CMAKE_C_FLAGS}
-               -DCMAKE_CXX_COMPILER=${CMAKE_CXX_COMPILER}
-               -DCMAKE_CXX_FLAGS=${ROOT_EXTERNAL_CXX_FLAGS}
-               -DCMAKE_INSTALL_PREFIX=${CMAKE_INSTALL_PREFIX}
-    INSTALL_COMMAND env DESTDIR=${Vc_DESTDIR} ${CMAKE_COMMAND} --build . --target install
-    TIMEOUT 600
-  )
-
-  set(VC_TARGET Vc)
-  set(Vc_LIBRARIES Vc)
-  set(Vc_INCLUDE_DIR ${Vc_ROOTDIR}/include)
-  set(Vc_CMAKE_MODULES_DIR ${Vc_ROOTDIR}/lib/cmake/Vc)
-
-  add_library(VcExt STATIC IMPORTED)
-  set_property(TARGET VcExt PROPERTY IMPORTED_LOCATION ${Vc_LIBRARY})
-  add_dependencies(VcExt VC)
-
-  add_library(Vc INTERFACE)
-  target_include_directories(Vc SYSTEM BEFORE INTERFACE $<BUILD_INTERFACE:${Vc_INCLUDE_DIR}>)
-  target_link_libraries(Vc INTERFACE VcExt)
-
-  find_package_handle_standard_args(Vc
-    FOUND_VAR Vc_FOUND
-    REQUIRED_VARS Vc_INCLUDE_DIR Vc_LIBRARIES Vc_CMAKE_MODULES_DIR
-    VERSION_VAR Vc_VERSION)
-
-  # FIXME: This is a workaround to let ROOT find the headers at runtime if
-  # they are in the build directory. This is necessary until we decide how to
-  # treat externals with headers used by ROOT
-  if(NOT EXISTS ${CMAKE_BINARY_DIR}/include/Vc)
-    if (NOT EXISTS ${CMAKE_BINARY_DIR}/include)
-      execute_process(COMMAND ${CMAKE_COMMAND} -E make_directory ${CMAKE_BINARY_DIR}/include)
-    endif()
-    execute_process(COMMAND ${CMAKE_COMMAND} -E create_symlink
-      ${Vc_INCLUDE_DIR}/Vc ${CMAKE_BINARY_DIR}/include/Vc)
-  endif()
-  # end of workaround
-
-  install(DIRECTORY ${Vc_ROOTDIR}/ DESTINATION ".")
-endif()
-
-if(Vc_FOUND)
-  # Missing from VcConfig.cmake
-  set(Vc_INCLUDE_DIRS ${Vc_INCLUDE_DIR})
-endif()
-
-#---Check for VecCore--------------------------------------------------------------------
-if(builtin_veccore)
-  unset(VecCore_FOUND)
-  unset(VecCore_FOUND CACHE)
-  set(veccore ON CACHE BOOL "Enabled because builtin_veccore requested (${veccore_description})" FORCE)
-elseif(veccore)
-  if(vc)
-    set(VecCore_COMPONENTS Vc)
-  endif()
-  if(fail-on-missing)
-    find_package(VecCore 0.4.2 CONFIG QUIET REQUIRED COMPONENTS ${VecCore_COMPONENTS})
-  else()
-    find_package(VecCore 0.4.2 CONFIG QUIET COMPONENTS ${VecCore_COMPONENTS})
-    if(NOT VecCore_FOUND)
-      ROOT_CHECK_CONNECTION("veccore=OFF")
-      if(NO_CONNECTION)
-        message(STATUS "VecCore not found and no internet connection, disabling the 'veccore' option")
-        set(veccore OFF CACHE BOOL "Disabled because not found and No internet connection" FORCE)
-      else()
-        message(STATUS "VecCore not found, switching on 'builtin_veccore' option.")
-        set(builtin_veccore ON CACHE BOOL "Enabled because veccore requested and not found externally (${builtin_veccore_description})" FORCE)
-      endif()
-    endif()
-  endif()
-  if(VecCore_FOUND)
-      set_property(DIRECTORY APPEND PROPERTY INCLUDE_DIRECTORIES ${VecCore_INCLUDE_DIRS})
-  endif()
-endif()
-
-if(builtin_veccore)
-  ROOT_CHECK_CONNECTION_AND_DISABLE_OPTION("builtin_veccore")
-endif()
-
-if(builtin_veccore)
-  set(VecCore_VERSION "0.8.2")
-  set(VecCore_PROJECT "VecCore-${VecCore_VERSION}")
-  set(VecCore_SRC_URI "${lcgpackages}/${VecCore_PROJECT}.tar.gz")
-  set(VecCore_DESTDIR "${CMAKE_BINARY_DIR}/externals")
-  set(VecCore_ROOTDIR "${VecCore_DESTDIR}/${CMAKE_INSTALL_PREFIX}")
-
-  ExternalProject_Add(VECCORE
-    URL     ${VecCore_SRC_URI}
-    URL_HASH SHA256=1268bca92acf00acd9775f1e79a2da7b1d902733d17e283e0dd5e02c41ac9666
-    BUILD_IN_SOURCE 0
-    LOG_DOWNLOAD 1 LOG_CONFIGURE 1 LOG_BUILD 1 LOG_INSTALL 1 LOG_OUTPUT_ON_FAILURE 1
-    CMAKE_ARGS -G ${CMAKE_GENERATOR}
-               -DBUILD_TESTING=OFF
-               -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}
-               -DCMAKE_C_COMPILER=${CMAKE_C_COMPILER}
-               -DCMAKE_C_FLAGS=${CMAKE_C_FLAGS}
-               -DCMAKE_CXX_COMPILER=${CMAKE_CXX_COMPILER}
-               -DCMAKE_CXX_FLAGS=${ROOT_EXTERNAL_CXX_FLAGS}
-               -DCMAKE_INSTALL_PREFIX=${CMAKE_INSTALL_PREFIX}
-    INSTALL_COMMAND env DESTDIR=${VecCore_DESTDIR} ${CMAKE_COMMAND} --build . --target install
-    TIMEOUT 600
-  )
-
-  set(VECCORE_TARGET VecCore)
-  set(VecCore_LIBRARIES VecCore)
-  list(APPEND VecCore_INCLUDE_DIRS ${VecCore_ROOTDIR}/include)
-
-  add_library(VecCore INTERFACE)
-  target_include_directories(VecCore SYSTEM INTERFACE $<BUILD_INTERFACE:${VecCore_ROOTDIR}/include>)
-  add_dependencies(VecCore VECCORE)
-
-  if (Vc_FOUND)
-    set(VecCore_Vc_FOUND True)
-    set(VecCore_Vc_DEFINITIONS -DVECCORE_ENABLE_VC)
-    set(VecCore_Vc_INCLUDE_DIR ${Vc_INCLUDE_DIR})
-    set(VecCore_Vc_LIBRARIES ${Vc_LIBRARIES})
-
-    set(VecCore_DEFINITIONS ${VecCore_Vc_DEFINITIONS})
-    list(APPEND VecCore_INCLUDE_DIRS ${VecCore_Vc_INCLUDE_DIR})
-    set(VecCore_LIBRARIES ${VecCore_LIBRARIES} ${Vc_LIBRARIES})
-    target_link_libraries(VecCore INTERFACE ${Vc_LIBRARIES})
-  endif()
-
-  find_package_handle_standard_args(VecCore
-    FOUND_VAR VecCore_FOUND
-    REQUIRED_VARS VecCore_INCLUDE_DIRS VecCore_LIBRARIES
-    VERSION_VAR VecCore_VERSION)
-
-  # FIXME: This is a workaround to let ROOT find the headers at runtime if
-  # they are in the build directory. This is necessary until we decide how to
-  # treat externals with headers used by ROOT
-  if(NOT EXISTS ${CMAKE_BINARY_DIR}/include/VecCore)
-    if (NOT EXISTS ${CMAKE_BINARY_DIR}/include)
-      execute_process(COMMAND ${CMAKE_COMMAND} -E make_directory ${CMAKE_BINARY_DIR}/include)
-    endif()
-    execute_process(COMMAND ${CMAKE_COMMAND} -E create_symlink
-      ${VecCore_ROOTDIR}/include/VecCore ${CMAKE_BINARY_DIR}/include/VecCore)
-  endif()
-  # end of workaround
-
-  install(DIRECTORY ${VecCore_ROOTDIR}/ DESTINATION ".")
-endif()
-
 if(builtin_vdt)
   ROOT_CHECK_CONNECTION_AND_DISABLE_OPTION("builtin_vdt")
 endif()
@@ -1626,12 +1438,6 @@ endif()
 if (vecgeom)
   message(STATUS "Looking for VecGeom")
   find_package(VecGeom 1.2 CONFIG)
-  if(builtin_veccore)
-    message(WARNING "ROOT must be built against the VecCore installation that was used to build VecGeom; builtin_veccore cannot be used. Option VecGeom will be disabled.")
-    set(vecgeom OFF CACHE BOOL "Disabled because non-builtin VecGeom specified but its VecCore cannot be found" FORCE)
-  elseif(builtin_veccore AND fail-on-missing)
-    message(SEND_ERROR "ROOT must be built against the VecCore installation that was used to build VecGeom; builtin_veccore cannot be used. Ensure that builtin_veccore option is OFF.")
-  endif()
   if(NOT VecGeom_FOUND )
     if(fail-on-missing)
       message(SEND_ERROR "VecGeom not found. Ensure that the installation of VecGeom is in the CMAKE_PREFIX_PATH")

@@ -37,9 +37,8 @@
 #@hasxft@ R__HAS_XFT    /**/
 #@hasclad@ R__HAS_CLAD    /**/
 #@hascocoa@ R__HAS_COCOA    /**/
-#@hasvc@ R__HAS_VC    /**/
 #@hasvdt@ R__HAS_VDT    /**/
-#@hasveccore@ R__HAS_VECCORE    /**/
+#@hasstdsimd@ R__HAS_STD_SIMD    /**/
 #@usecxxmodules@ R__USE_CXXMODULES   /**/
 #@uselibc++@ R__USE_LIBCXX    /**/
 #@has_found_attribute_always_inline@ R__HAS_ATTRIBUTE_ALWAYS_INLINE /**/
@@ -54,12 +53,6 @@
 #@use_less_includes@ R__LESS_INCLUDES /**/
 #define R__HARDWARE_INTERFERENCE_SIZE @hardwareinterferencesize@ /*Determined at CMake configure to be stable across all TUs*/
 
-#if defined(R__HAS_VECCORE) && defined(R__HAS_VC)
-#ifndef VECCORE_ENABLE_VC
-#define VECCORE_ENABLE_VC
-#endif
-#endif
-
 #@uselz4@ R__HAS_DEFAULT_LZ4  /**/
 #@usezlib@ R__HAS_DEFAULT_ZLIB  /**/
 #@uselzma@ R__HAS_DEFAULT_LZMA  /**/