[Offload] Add Sphinx HTML documentation target

Introduces the `docs-offload-html` target when CMake is configured with
`LLVM_ENABLE_SPHINX=ON` and `SPHINX_OUTPUT_HTML=ON`. Utilized
`offload-tblgen -gen-spen` to generate Offload API specification docs.

Author: kbenzie

offload/CMakeLists.txt

@@ -23,6 +23,8 @@ elseif(NOT CMAKE_SIZEOF_VOID_P EQUAL 8)
   return()
 endif()
 
+set(OFFLOAD_SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR})
+
 if(OPENMP_STANDALONE_BUILD)
   set(OFFLOAD_LIBDIR_SUFFIX "" CACHE STRING
     "Suffix of lib installation directory, e.g. 64 => lib64")
@@ -371,6 +373,7 @@ add_subdirectory(tools/offload-tblgen)
 add_subdirectory(plugins-nextgen)
 add_subdirectory(DeviceRTL)
 add_subdirectory(tools)
+add_subdirectory(docs)
 
 # Build target agnostic offloading library.
 add_subdirectory(libomptarget)

offload/docs/.gitignore

@@ -0,0 +1 @@
+offload-api.rst

offload/docs/CMakeLists.txt

@@ -0,0 +1,25 @@
+if(LLVM_ENABLE_SPHINX)
+  include(AddSphinxTarget)
+  if(SPHINX_FOUND AND SPHINX_OUTPUT_HTML)
+    # Generate offload-api.rst from OffloadAPI.td
+    set(LLVM_TARGET_DEFINITIONS
+      ${OFFLOAD_SOURCE_DIR}/liboffload/API/OffloadAPI.td)
+    tablegen(OFFLOAD source/offload-api.rst -gen-spec
+      EXTRA_INCLUDES ${OFFLOAD_SOURCE_DIR}/liboffload/API)
+    add_public_tablegen_target(OffloadDocsGenerate)
+
+    # Due to Sphinx only allowing a single source direcotry and the fact we
+    # only generate a single file, copy offload-api.rst to the source directory
+    # to be included in the generated documentation. A .gitignore file ensures
+    # offload-api.rst will not be added to the repository.
+    add_custom_target(OffloadDocsCopy
+      COMMAND ${CMAKE_COMMAND} -E copy
+        ${CMAKE_CURRENT_BINARY_DIR}/source/offload-api.rst
+        ${CMAKE_CURRENT_SOURCE_DIR}/offload-api.rst)
+
+    # Generate the HTML documentation, invoked wt the docs-offload-html target.
+    add_sphinx_target(html offload
+      SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR})
+    add_dependencies(docs-offload-html OffloadDocsGenerate OffloadDocsCopy)
+  endif()
+endif()

offload/docs/conf.py

@@ -0,0 +1,31 @@
+# Configuration file for the Sphinx documentation builder.
+#
+# For the full list of built-in configuration values, see the documentation:
+# https://www.sphinx-doc.org/en/master/usage/configuration.html
+
+# -- Project information -----------------------------------------------------
+# https://www.sphinx-doc.org/en/master/usage/configuration.html#project-information
+
+project = "Offload"
+copyright = "2025, LLVM project"
+author = "LLVM project"
+
+# -- General configuration ---------------------------------------------------
+# https://www.sphinx-doc.org/en/master/usage/configuration.html#general-configuration
+
+extensions = []
+
+templates_path = ["_templates"]
+exclude_patterns = []
+
+# -- C domain configuration --------------------------------------------------
+# https://www.sphinx-doc.org/en/master/usage/configuration.html#c-config
+
+c_maximum_signature_line_length = 60
+
+# -- Options for HTML output -------------------------------------------------
+# https://www.sphinx-doc.org/en/master/usage/configuration.html#options-for-html-output
+
+html_theme = "llvm-theme"
+html_theme_path = ["_themes"]
+html_static_path = ["_static"]

offload/docs/index.rst

@@ -0,0 +1,21 @@
+.. Offload documentation master file, created by
+   sphinx-quickstart on Fri Jul  4 14:59:13 2025.
+   You can adapt this file completely to your liking, but it should at least
+   contain the root `toctree` directive.
+
+Welcome to Offload's documentation!
+===================================
+
+.. toctree::
+   :maxdepth: 2
+   :caption: Contents:
+
+   offload-api
+
+
+Indices and tables
+==================
+
+* :ref:`genindex`
+* :ref:`modindex`
+* :ref:`search`