root-project · guitargeek · Dec 18, 2025 · Dec 17, 2025 · Dec 17, 2025 · Dec 19, 2025
@@ -24,9 +24,8 @@ builtin_openui5=ON
 builtin_pcre=OFF
 builtin_tbb=OFF
 builtin_unuran=OFF
-builtin_vc=OFF
 builtin_vdt=OFF
-builtin_veccore=OFF
+builtin_veccore=ON
 builtin_xrootd=OFF
 builtin_xxhash=OFF
 builtin_zeromq=ON
@@ -97,9 +96,8 @@ tmva=ON
 unfold=ON
 unuran=ON
 uring=OFF
-vc=OFF
 vdt=ON
-veccore=OFF
+veccore=ON
 vecgeom=OFF
 webgui=ON
 win_broken_tests=OFF

@@ -18,7 +18,6 @@ builtin_openssl=ON
 builtin_pcre=ON
 builtin_tbb=ON
 builtin_unuran=ON
-builtin_vc=ON
 builtin_vdt=ON
 builtin_veccore=ON
 builtin_xrootd=ON

@@ -156,7 +156,7 @@
          INCREMENTAL: ${{ !contains(github.event.pull_request.labels.*.name, 'clean build') && !matrix.platform == 'mac15' && !matrix.platform == 'mac26'}}
          GITHUB_PR_ORIGIN: ${{ github.event.pull_request.head.repo.clone_url }}
          OVERRIDES: ${{ join( matrix.overrides, ' ') }}
        run: |
          [ -d "${VIRTUAL_ENV_DIR}" ] && source ${VIRTUAL_ENV_DIR}/bin/activate
          echo "Python is now $(which python3) $(python3 --version)"
          src/.github/workflows/root-ci-config/build_root.py  \
@@ -286,7 +286,7 @@
          INCREMENTAL: ${{ !contains(github.event.pull_request.labels.*.name, 'clean build') }}
          GITHUB_PR_ORIGIN: ${{ github.event.pull_request.head.repo.clone_url }}
        shell: cmd
        run: "C:\\setenv.bat ${{ matrix.target_arch }} &&
              python .github/workflows/root-ci-config/build_root.py
                    --buildtype       ${{ matrix.config }}
                    --platform        windows10
@@ -402,7 +402,7 @@
           - image: alma9
             is_special: true
             property: march_native
-            overrides: ["CMAKE_BUILD_TYPE=RelWithDebInfo", "CMAKE_CXX_FLAGS=-march=native", "CMAKE_C_FLAGS=-march=native", "builtin_zlib=ON", "builtin_zstd=ON"]
+            overrides: ["CMAKE_BUILD_TYPE=RelWithDebInfo", "CMAKE_CXX_FLAGS=-march=native", "CMAKE_C_FLAGS=-march=native", "builtin_zlib=ON", "builtin_zstd=ON", "builtin_veccore=ON", "veccore=ON"]
           - image: alma10
             is_special: true
             property: arm64
@@ -428,7 +428,7 @@
      - self-hosted
      - linux
      - ${{ matrix.architecture == null && 'x64' || matrix.architecture }}
      - ${{ matrix.extra-runs-on == null && 'cpu' || matrix.extra-runs-on }}

    name: |
      ${{ matrix.image }} ${{ matrix.property }}

@@ -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

@@ -107,7 +107,6 @@ 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)")
@@ -180,7 +179,6 @@ 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")
@@ -253,7 +251,6 @@ 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)
@@ -295,7 +292,6 @@ 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)
@@ -415,6 +411,35 @@ if(DEFINED rpath)
       "") # empty line at the end to make the deprecation message more visible
 endif()
 
+foreach(opt vc builtin_vc)
+  if(${opt})
+    message(DEPRECATION ">>> Option '${opt}' is deprecated and ignored."
+        "ROOT now uses std::simd for the vectorized TFormula and TMath classes when available (Clang or GCC >= 9)."
+        "Using this option will result in configuration errors in ROOT 6.42.")
+  endif()
+endforeach()
+
+foreach(opt veccore builtin_veccore)
+  # Disable VecCore if we don't support it for a given platform.
+  # We try to give clear explanations here in all distinct cases.
+  if(${opt})
+    if(WIN32)
+      message(WARNING "ROOT option '${opt}' will be disabled. Using VecCore on Windows is not supported by ROOT.")
+      set(${opt} OFF CACHE BOOL "Disabled because VecCore is not supported on Windows." FORCE)
+    elseif(APPLE AND CMAKE_SYSTEM_PROCESSOR STREQUAL "x86_64")
+      message(WARNING "ROOT option '${opt}' will be disabled. We don't support using VecCore on Apple with Intel hardware anymore.")
+      set(${opt} OFF CACHE BOOL "Disabled because VecCore is not supported on Apple with Intel hardware." FORCE)
+    elseif(APPLE)
+      message(WARNING "ROOT option '${opt}' will be disabled. We don't support using VecCore on Apple silicon, as std::simd is not available for Apple Clang and the old Vc backend also didn't support Apple silicon anyway.")
+      set(${opt} OFF CACHE BOOL "Disabled because VecCore is not supported on Apple silicon." FORCE)
+    elseif(CMAKE_CXX_COMPILER_ID STREQUAL "GNU"
+           AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 9)
+      message(WARNING "ROOT option '${opt}' will be disabled. GCC versions older than 9 do not provide std::simd, and the Vc backend of VecCore is not supported anymore by ROOT.")
+      set(${opt} OFF CACHE BOOL "Disabled because VecCore is not supported on GCC < 9." FORCE)
+    endif()
+  endif()
+endforeach()
+
 foreach(opt minuit2_mpi)
   if(${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.")

@@ -365,11 +365,6 @@ if(cocoa)
 else()
   set(hascocoa undef)
 endif()
-if(vc)
-  set(hasvc define)
-else()
-  set(hasvc undef)
-endif()
 if(vdt)
   set(hasvdt define)
 else()

@@ -1365,106 +1365,12 @@ 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()
@@ -1521,18 +1427,6 @@ if(builtin_veccore)
   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

@@ -37,7 +37,6 @@
 #@hasxft@ R__HAS_XFT    /**/
 #@hasclad@ R__HAS_CLAD    /**/
 #@hascocoa@ R__HAS_COCOA    /**/
-#@hasvc@ R__HAS_VC    /**/
 #@hasvdt@ R__HAS_VDT    /**/
 #@hasveccore@ R__HAS_VECCORE    /**/
 #@usecxxmodules@ R__USE_CXXMODULES   /**/
@@ -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  /**/

@@ -116,9 +116,6 @@ set(clinginclude ${CMAKE_SOURCE_DIR}/interpreter/cling/include)
 set(custom_modulemaps)
 if (runtime_cxxmodules)
   set(custom_modulemaps boost.modulemap tinyxml2.modulemap cuda.modulemap module.modulemap.build)
-  if(vc)
-    set(custom_modulemaps ${custom_modulemaps} vc.modulemap)
-  endif()
 
   # We need to override the default modulemap because instead of producing a
   # single std.pcm, produces hundreds of pcms. This changed with MacOSX14.4.sdk

@@ -10,9 +10,6 @@
 ############################################################################
 
 include_directories(AFTER SYSTEM ${VECGEOM_INCLUDE_DIRS})
-if ( Vc_FOUND )
-   include_directories( AFTER SYSTEM ${Vc_INCLUDE_DIRS})
-endif()
 
 ROOT_STANDARD_LIBRARY_PACKAGE(ConverterVG
   HEADERS

@@ -373,11 +373,7 @@ namespace ROOT {
             // case of polynomial function (no parameter dependency)  (case for dim = 1)
             assert(fDim == 1);
             if (ipar == 0) return 1.0;
-#ifdef R__HAS_VECCORE
-            return vecCore::math::Pow(x[0], static_cast<T>(ipar));
-#else
-            return std::pow(x[0], static_cast<int>(ipar));
-#endif
+            return pow(x[0], static_cast<int>(ipar));
          } else {
             // case of general linear function (built in TFormula with ++ )
             return GeneralLinearFunctionDerivation<T>::DoParameterDerivative(this, x, ipar);

@@ -841,7 +841,7 @@ inline double TF1::EvalParVec(const Double_t *data, const Double_t *params)
       //    res = GetSave(x);
       return TMath::SignalingNaN();
    }
-   return vecCore::Get<ROOT::Double_v>(res, 0);
+   return res[0];
 }
 #endif
 

@@ -123,7 +123,6 @@ class TFormula : public TNamed
    static Bool_t   IsDefaultVariableName(const TString &name);
    void ReplaceAllNames(TString &formula, std::map<TString, TString> &substitutions);
    void FillParametrizedFunctions(std::map<std::pair<TString, Int_t>, std::pair<TString, TString>> &functions);
-   void FillVecFunctionsShurtCuts();
    void ReInitializeEvalMethod();
    std::string GetGradientFuncName() const {
       return std::string(GetUniqueFuncName().Data()) + "_grad_1";