[OpenMP] Remove LLVM_ENABLE_PROJECTS=openmp build mode (#176950)

Meinersbur · web-flow · commit c15853ec3a30 · 2026-01-30T21:05:29.000+01:00
Reapply #152189 and #174963 which were reverted because it broke publish-sphinx-docs and publish-doxygen-docs. The build mode has been deprecated in #136314 and was supposed to be removed in the LLVM 21 release (#136314). OpenMP currently supports 4 build modes: * `cmake <llvm-project>/llvm -DLLVM_ENABLE_PROJECTS=openmp` * `cmake <llvm-project>/llvm -DLLVM_ENABLE_RUNTIMES=openmp` (bootstrapping build) * `cmake <llvm-project>/openmp` (standalone build) * `cmake <llvm-project>/runtimes -DLLVM_ENABLE_RUNTIMES=openmp` (runtimes default/standalone build) Each build mode increased the maintanance overhead since all build modes must continue working and user confusion when there do not (see #151117, #174126, #154117, ...). Let's finally remove it.
diff --git a/.github/workflows/docs.yml b/.github/workflows/docs.yml
@@ -186,10 +186,10 @@ jobs:
           steps.docs-changed-subprojects.outputs.openmp_any_changed == 'true' ||
           steps.docs-changed-subprojects.outputs.workflow_any_changed == 'true'
         run: |
-          cmake -B openmp-build -GNinja -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_PROJECTS="clang;openmp" -DLLVM_ENABLE_SPHINX=ON ./llvm
+          cmake -B openmp-build -GNinja -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_RUNTIMES="openmp" -DLLVM_ENABLE_SPHINX=ON -DLLVM_INCLUDE_TESTS=OFF ./runtimes
           TZ=UTC ninja -C openmp-build docs-openmp-html
           mkdir built-docs/openmp
-          cp -r openmp-build/docs/* built-docs/openmp/
+          cp -r openmp-build/openmp/docs/* built-docs/openmp/
       - name: Build Polly docs
         if: |
           steps.docs-changed-subprojects.outputs.polly_any_changed == 'true' ||
diff --git a/clang/utils/analyzer/entrypoint.py b/clang/utils/analyzer/entrypoint.py
@@ -53,8 +53,8 @@ def is_cmake_needed():
 CMAKE_COMMAND = (
     "cmake -G Ninja -DCMAKE_BUILD_TYPE=Release "
     "-DCMAKE_INSTALL_PREFIX=/analyzer -DLLVM_TARGETS_TO_BUILD=X86 "
-    '-DLLVM_ENABLE_PROJECTS="clang;openmp" -DLLVM_BUILD_RUNTIME=OFF '
-    "-DCLANG_ENABLE_STATIC_ANALYZER=ON"
+    '-DLLVM_ENABLE_PROJECTS="clang" -DLLVM_ENABLE_RUNTIMES="openmp" '
+    "-DLLVM_BUILD_RUNTIME=OFF -DCLANG_ENABLE_STATIC_ANALYZER=ON"
 )
 
 
diff --git a/flang-rt/README.md b/flang-rt/README.md
@@ -58,8 +58,8 @@ not provide all C-ABI functionality (such as Windows).
 cmake -S <path-to-llvm-project-source>/llvm     \
   -GNinja                                       \
   -DCMAKE_BUILD_TYPE=Release                    \
-  -DLLVM_ENABLE_PROJECTS="clang;flang;openmp"   \
-  -DLLVM_ENABLE_RUNTIMES="compiler-rt;flang-rt" \
+  -DLLVM_ENABLE_PROJECTS="clang;flang"   \
+  -DLLVM_ENABLE_RUNTIMES="compiler-rt;flang-rt;openmp" \
   ...
 ```
 
diff --git a/flang/tools/f18/CMakeLists.txt b/flang/tools/f18/CMakeLists.txt
@@ -135,18 +135,7 @@ if (NOT CMAKE_CROSSCOMPILING)
   # Special case for omp_lib.mod, because its source comes from openmp/runtime/src/include.
   # It also produces two module files: omp_lib.mod and omp_lib_kinds.mod.  Compile these
   # files only if OpenMP support has been configured.
-  if (LLVM_TOOL_OPENMP_BUILD)
-    message(STATUS "OpenMP runtime support enabled via LLVM_ENABLE_PROJECTS, building omp_lib.mod")
-    set(base ${FLANG_INTRINSIC_MODULES_DIR}/omp_lib)
-    add_custom_command(OUTPUT ${base}.mod ${base}_kinds.mod
-      COMMAND ${CMAKE_COMMAND} -E make_directory ${FLANG_INTRINSIC_MODULES_DIR}
-      COMMAND flang -cpp -fsyntax-only ${opts} -module-dir ${FLANG_INTRINSIC_MODULES_DIR}
-        ${CMAKE_BINARY_DIR}/projects/openmp/runtime/src/omp_lib.F90
-      DEPENDS flang ${FLANG_INTRINSIC_MODULES_DIR}/iso_c_binding.mod ${CMAKE_BINARY_DIR}/projects/openmp/runtime/src/omp_lib.F90 ${depends}
-    )
-    list(APPEND MODULE_FILES ${base}.mod ${base}_kinds.mod)
-    install(FILES ${base}.mod ${base}_kinds.mod DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/flang" COMPONENT flang-module-interfaces)
-  elseif ("openmp" IN_LIST LLVM_ENABLE_RUNTIMES)
+  if ("openmp" IN_LIST LLVM_ENABLE_RUNTIMES)
     message(STATUS "OpenMP runtime support enabled via LLVM_ENABLE_RUNTIMES, assuming omp_lib.mod is built there")
   else()
     message(WARNING "Not building omp_lib.mod, no OpenMP runtime in either LLVM_ENABLE_PROJECTS or LLVM_ENABLE_RUNTIMES")
@@ -160,11 +149,7 @@ set_target_properties(module_files PROPERTIES FOLDER "Flang/Resources")
 
 # TODO Move this to a more suitable location
 # Copy the generated omp_lib.h header file, if OpenMP support has been configured.
-if (LLVM_TOOL_OPENMP_BUILD)
-  message(STATUS "OpenMP runtime support enabled via LLVM_ENABLE_PROJECTS, building omp_lib.h")
-  file(COPY ${CMAKE_BINARY_DIR}/projects/openmp/runtime/src/omp_lib.h DESTINATION "${CMAKE_BINARY_DIR}/include/flang/OpenMP/" FILE_PERMISSIONS OWNER_READ OWNER_WRITE)
-  install(FILES ${CMAKE_BINARY_DIR}/include/flang/OpenMP/omp_lib.h DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/flang/OpenMP")
-elseif ("openmp" IN_LIST LLVM_ENABLE_RUNTIMES)
+if ("openmp" IN_LIST LLVM_ENABLE_RUNTIMES)
   message(STATUS "OpenMP runtime support enabled via LLVM_ENABLE_RUNTIMES, assuming omp_lib.h is built there")
 else()
   message(STATUS "Not copying omp_lib.h, no OpenMP runtime in either LLVM_ENABLE_PROJECTS or LLVM_ENABLE_RUNTIMES")
diff --git a/llvm/CMakeLists.txt b/llvm/CMakeLists.txt
@@ -104,12 +104,7 @@ endif()
 # This allows an easy way of setting up a build directory for llvm and another
 # one for llvm+clang+... using the same sources.
 # These projects will be included when "all" is included in LLVM_ENABLE_PROJECTS.
-set(LLVM_ALL_PROJECTS "bolt;clang;clang-tools-extra;compiler-rt;cross-project-tests;libclc;lld;lldb;mlir;openmp;polly")
-if ("${CMAKE_SYSTEM_NAME}" MATCHES "AIX")
-  # Disallow 'openmp' as a LLVM PROJECT on AIX as the supported way is to use
-  # LLVM_ENABLE_RUNTIMES.
-  list(REMOVE_ITEM LLVM_ALL_PROJECTS openmp)
-endif()
+set(LLVM_ALL_PROJECTS "bolt;clang;clang-tools-extra;compiler-rt;cross-project-tests;libclc;lld;lldb;mlir;polly")
 
 # The "libc" project, which is not part of "all" projects, could be included in
 # LLVM_ENABLE_PROJECTS.  It is preferred to include "libc" in
@@ -126,6 +121,15 @@ if( LLVM_ENABLE_PROJECTS STREQUAL "all" )
   set( LLVM_ENABLE_PROJECTS ${LLVM_ALL_PROJECTS})
 endif()
 
+if ("openmp" IN_LIST LLVM_ENABLE_PROJECTS)
+  message(FATAL_ERROR "
+Support for the LLVM_ENABLE_PROJECTS=openmp build mode has been removed. Please switch to the bootstrapping build
+    cmake -S <llvm-project>/llvm -B build -DLLVM_ENABLE_PROJECTS=clang -DLLVM_ENABLE_RUNTIMES=openmp
+or to the runtimes default build
+    cmake -S <llvm-project>/runtimes -B build -DLLVM_ENABLE_RUNTIMES=openmp
+")
+endif()
+
 foreach(proj ${LLVM_ENABLE_PROJECTS})
   if (NOT proj STREQUAL "llvm" AND NOT "${proj}" IN_LIST LLVM_KNOWN_PROJECTS)
      MESSAGE(FATAL_ERROR "${proj} isn't a known project: ${LLVM_KNOWN_PROJECTS}. Did you mean to enable it as a runtime in LLVM_ENABLE_RUNTIMES?")
@@ -195,13 +199,6 @@ if ("offload" IN_LIST LLVM_ENABLE_PROJECTS)
     "https://openmp.llvm.org/ for building the runtimes.")
 endif()
 
-if ("openmp" IN_LIST LLVM_ENABLE_PROJECTS)
-  message(WARNING "Using LLVM_ENABLE_PROJECTS=openmp is deprecated now, and will "
-    "become a fatal error in a future release.  Please use "
-    "-DLLVM_ENABLE_RUNTIMES=openmp or see the instructions at "
-    "https://openmp.llvm.org/ for building the runtimes.")
-endif()
-
 if ("flang-rt" IN_LIST LLVM_ENABLE_RUNTIMES)
   if (NOT "flang" IN_LIST LLVM_ENABLE_PROJECTS)
     message(FATAL_ERROR "Flang is not enabled, but is required for the Flang-RT runtime")
diff --git a/llvm/runtimes/CMakeLists.txt b/llvm/runtimes/CMakeLists.txt
@@ -700,13 +700,6 @@ if(build_runtimes)
     # We need to add the runtimes as a dependency because compiler-rt can be
     # built as part of runtimes and we need the profile runtime for PGO
     add_dependencies(clang-bootstrap-deps runtimes)
-    # The bootstrap build will attempt to configure the offload runtime
-    # before the openmp project which will error out due to failing to
-    # find libomp.so. We must add omp as a dependency before runtimes
-    # are configured.
-    if("openmp" IN_LIST LLVM_ENABLE_PROJECTS AND "offload" IN_LIST LLVM_ENABLE_RUNTIMES)
-      add_dependencies(clang-bootstrap-deps omp)
-    endif()
   endif()
 
   if(LLVM_INCLUDE_TESTS)
diff --git a/openmp/docs/ReleaseNotes.rst b/openmp/docs/ReleaseNotes.rst
@@ -27,3 +27,4 @@ Device Runtime
   always build support for AMDGPU and NVPTX targets.
 - Updated the offloading entry format but retained backwards compatibility with
   the old format.
+- The LLVM_ENABLE_PROJECTS=openmp build mode has been removed.

Original file line number	Diff line number	Diff line change
`@@ -53,8 +53,8 @@ def is_cmake_needed():`
`53`	`53`	`CMAKE_COMMAND = (`
`54`	`54`	`"cmake -G Ninja -DCMAKE_BUILD_TYPE=Release "`
`55`	`55`	`"-DCMAKE_INSTALL_PREFIX=/analyzer -DLLVM_TARGETS_TO_BUILD=X86 "`
`56`		`- '-DLLVM_ENABLE_PROJECTS="clang;openmp" -DLLVM_BUILD_RUNTIME=OFF '`
`57`		`- "-DCLANG_ENABLE_STATIC_ANALYZER=ON"`
	`56`	`+ '-DLLVM_ENABLE_PROJECTS="clang" -DLLVM_ENABLE_RUNTIMES="openmp" '`
	`57`	`+ "-DLLVM_BUILD_RUNTIME=OFF -DCLANG_ENABLE_STATIC_ANALYZER=ON"`
`58`	`58`	`)`
`59`	`59`
`60`	`60`