Add top-level CMake kernels target (#12806)

Add a top level kernels CMake target, which includes all configured
kernel libraries. I validate this change by building a simple runner
using the executorch_kernels target and verifying that it was able to
build and run MobileNet v2, with and without selective build. Once the
changes land in ExecuTorch, this will be long-term validated in
executorch-examples CI.

There are a few follow-ups needed, which I will handle shortly. I still
need to add merging logic for the YAML files to generate a single
selective library that includes quantized and LLM ops, when configured
to build them.

This is done in the context of top-level CMake targets, tracked in
#12293.

Author: GregoryComer

CMakeLists.txt

@@ -123,6 +123,8 @@ set(CMAKE_INSTALL_RPATH_USE_LINK_PATH ON)
 # Instead please use `find_package(executorch REQUIRED)` in the example
 # directory and add a new executable in the example `CMakeLists.txt`.
 
+set(EXECUTORCH_ROOT ${CMAKE_CURRENT_SOURCE_DIR})
+
 if(NOT EXECUTORCH_ENABLE_LOGGING)
   # Avoid pulling in the logging strings, which can be large. Note that this
   # will set the compiler flag for all targets in this directory, and for all
@@ -386,6 +388,9 @@ set(_executorch_backends "")
 # A list of all configured extensions.
 set(_executorch_extensions "")
 
+# A list of all configured kernel libraries.
+set(_executorch_kernels "")
+
 target_link_libraries(executorch_core PRIVATE program_schema)
 if(ANDROID)
   target_link_libraries(executorch_core PUBLIC log)
@@ -774,11 +779,13 @@ endif()
 if(EXECUTORCH_BUILD_KERNELS_LLM)
   # TODO: move all custom kernels to ${CMAKE_CURRENT_SOURCE_DIR}/kernels/custom
   add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/extension/llm/custom_ops)
+  list(APPEND _executorch_kernels custom_ops_aot_lib)
 endif()
 
 if(EXECUTORCH_BUILD_KERNELS_QUANTIZED)
   add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/kernels/quantized)
   executorch_target_link_options_shared_lib(quantized_ops_lib)
+  list(APPEND _executorch_kernels quantized_ops_lib)
 endif()
 
 if(EXECUTORCH_BUILD_VULKAN)
@@ -803,6 +810,60 @@ add_library(executorch_extensions INTERFACE)
 add_library(executorch::extensions ALIAS executorch_extensions)
 target_link_libraries(executorch_extensions INTERFACE ${_executorch_extensions})
 
+# A target containing all configured kernels, with selective build, if enabled.
+add_library(executorch_kernels INTERFACE)
+add_library(executorch::kernels ALIAS executorch_kernels)
+if(NOT EXECUTORCH_SELECT_OPS_YAML STREQUAL ""
+   OR NOT EXECUTORCH_SELECT_OPS_LIST STREQUAL ""
+   OR NOT EXECUTORCH_SELECT_OPS_MODEL STREQUAL ""
+)
+  gen_selected_ops(
+    LIB_NAME
+    "executorch_selected_kernels"
+    OPS_SCHEMA_YAML
+    "${EXECUTORCH_SELECT_OPS_LIB}"
+    ROOT_OPS
+    "${EXECUTORCH_SELECT_OPS_LIST}"
+    INCLUDE_ALL_OPS
+    FALSE
+    OPS_FROM_MODEL
+    "${EXECUTORCH_SELECT_OPS_MODEL}"
+    DTYPE_SELECTIVE_BUILD
+    "${EXECUTORCH_ENABLE_DTYPE_SELECTIVE_BUILD}"
+  )
+
+  generate_bindings_for_kernels(
+    LIB_NAME
+    "executorch_selected_kernels"
+    FUNCTIONS_YAML
+    ${EXECUTORCH_ROOT}/kernels/portable/functions.yaml
+    CUSTOM_OPS_YAML
+    ""
+    DTYPE_SELECTIVE_BUILD
+    "${EXECUTORCH_ENABLE_DTYPE_SELECTIVE_BUILD}"
+  )
+
+  gen_operators_lib(
+    LIB_NAME
+    "executorch_selected_kernels"
+    KERNEL_LIBS
+    "portable_kernels"
+    DEPS
+    executorch_core
+    DTYPE_SELECTIVE_BUILD
+    "${EXECUTORCH_ENABLE_DTYPE_SELECTIVE_BUILD}"
+  )
+  list(APPEND _executorch_kernels executorch_selected_kernels)
+else()
+  # No selective build - link the full library.
+  if(EXECUTORCH_BUILD_KERNELS_OPTIMIZED)
+    list(APPEND _executorch_kernels optimized_native_cpu_ops_lib)
+  else()
+    list(APPEND _executorch_kernels portable_ops_lib)
+  endif()
+endif()
+target_link_libraries(executorch_kernels INTERFACE ${_executorch_kernels})
+
 if(EXECUTORCH_BUILD_EXECUTOR_RUNNER)
   # Baseline libraries that executor_runner will link against.
   set(_executor_runner_libs executorch extension_evalue_util

tools/cmake/preset/default.cmake

@@ -214,6 +214,28 @@ define_overridable_option(
   EXECUTORCH_USE_CPP_CODE_COVERAGE "Build with code coverage enabled" BOOL OFF
 )
 
+# Selective build options. These affect the executorch_kernels target.
+define_overridable_option(
+  EXECUTORCH_SELECT_OPS_YAML
+  "Build the executorch_kernels target with YAML selective build config."
+  STRING ""
+)
+define_overridable_option(
+  EXECUTORCH_SELECT_OPS_LIST
+  "Build the executorch_kernels target with a list of selected operators."
+  STRING ""
+)
+define_overridable_option(
+  EXECUTORCH_SELECT_OPS_MODEL
+  "Build the executorch_kernels target with only operators from the given model .pte file."
+  STRING ""
+)
+define_overridable_option(
+  EXECUTORCH_ENABLE_DTYPE_SELECTIVE_BUILD
+  "Build the executorch_kernels target with only operator implementations for selected data types."
+  BOOL FALSE
+)
+
 # ------------------------------------------------------------------------------
 # Validations
 #
@@ -284,6 +306,17 @@ check_conflicting_options_on(
   EXECUTORCH_BUILD_CPUINFO
 )
 
+# Selective build specifiers are mutually exclusive.
+check_conflicting_options_on(
+  IF_ON EXECUTORCH_SELECT_OPS_YAML CONFLICTS_WITH
+  EXECUTORCH_SELECT_OPS_LIST EXECUTORCH_SELECT_OPS_MODEL
+)
+
+check_conflicting_options_on(
+  IF_ON EXECUTORCH_SELECT_OPS_LIST CONFLICTS_WITH
+  EXECUTORCH_SELECT_OPS_MODEL
+)
+
 if(NOT EXISTS ${EXECUTORCH_PAL_DEFAULT_FILE_PATH})
   message(
     FATAL_ERROR