[bootstrap build] Add libc-hdrgen as a build dep for libc bootstrap build.

[sivachandra]

Summary

With this change, libc-hdrgen is built like a host build tool like clang and used
to build libc for the target.

[phosek]

llvm/runtimes/CMakeLists.txt

368

This can have potentially negative side-effects. Take for example Fuchsia's CMake cache file where on Darwin we set the generic flags which are passed to the "default" build as well as prefixed flags which are passed to target build. With this change, the generic flags will be passed to the target build and interfere with the prefixed flags. Can we avoid this change for now?

[phosek]

llvm/runtimes/CMakeLists.txt

368

To add some additional context, I'm planning major changes to how the "default" and target builds are set up, and after those changes, this should be possible without any negative side-effects, but that's going to take a few more weeks.

[sivachandra]

llvm/runtimes/CMakeLists.txt

368

The other option is to detect the libc specific options and pass them as CMAKE_ARGS. For now, we only need to test for LLVM_LIBC_FULL_BUILD. If that is OK, then we can avoid depending on prefixes.

[sivachandra]

A friendly ping.

[phosek]

llvm/runtimes/CMakeLists.txt

368

That would be my preference, at least for now.

[sivachandra]

Use CMake args to pass options to the libc build.

[sivachandra]

llvm/runtimes/CMakeLists.txt

368

How does the latest diff look?

[sivachandra]

Friendly ping - how does the latest diff look?

[phosek]

llvm/runtimes/CMakeLists.txt

388–389

Nit: this is unnecessary (uninitialized variables in CMake evaluate to empty string).

397–398

This is slightly counterintuitive. I'd prefer introducing a special handling in llvm/CMakeLists.txt similarly to what we do for example for flang and mlir, see https://github.com/llvm/llvm-project/blob/830d116d776439093a16aad567cd3db2c4c3cd72/llvm/CMakeLists.txt#L143 and automatically including libc in LLVM_ENABLE_PROJECTS when libc is in LLVM_ENABLE_RUNTIMES.

[sivachandra]

Add "libc" to enabled projects if it is listed in enabled runtimes.

[sivachandra]

llvm/runtimes/CMakeLists.txt

397–398

I left this check here as a debug aid, but have also updated llvm/CMakeLists.txt according to your suggestion.

[phosek]

LGTM

[sivachandra]

Remove a spurious arg which was not removed when addressing the last round of comments.

llvm/CMakeLists.txt

if(LLVM_ENABLE_RUNTIMES STREQUAL "all")
   set(LLVM_ENABLE_RUNTIMES ${LLVM_DEFAULT_RUNTIMES})
 endif()
 foreach(proj IN LISTS LLVM_ENABLE_RUNTIMES)
   if (NOT "${proj}" IN_LIST LLVM_SUPPORTED_RUNTIMES)
     message(FATAL_ERROR "Runtime \"${proj}\" is not a supported runtime. Supported runtimes are: ${LLVM_SUPPORTED_RUNTIMES}")
   endif()
 endforeach()
 
+if ("libc" IN_LIST LLVM_ENABLE_RUNTIMES)
+  # To build the libc runtime, we need to be able to build few libc build
+  # tools from the "libc" project. So, we add it to the list of enabled
+  # projects.
+  if (NOT "libc" IN_LIST LLVM_ENABLE_PROJECTS)
+    message(STATUS "Enabling libc project to build libc build tools")
+    list(APPEND LLVM_ENABLE_PROJECTS "libc")
+  endif()
+endif()
+
 # LLVM_ENABLE_PROJECTS_USED is `ON` if the user has ever used the
 # `LLVM_ENABLE_PROJECTS` CMake cache variable.  This exists for
 # several reasons:
 #
 # * As an indicator that the `LLVM_ENABLE_PROJECTS` list is now the single
 # source of truth for which projects to build. This means we will ignore user
 # supplied `LLVM_TOOL_<project>_BUILD` CMake cache variables and overwrite
 # them.

llvm/runtimes/CMakeLists.txt

foreach(entry ${runtimes})
   string(FIND ${projName} "lib" LIB_IDX)
   if(LIB_IDX EQUAL 0 AND NOT projName STREQUAL "libc")
     string(SUBSTRING ${projName} 3 -1 projName)
   endif()
   list(APPEND runtime_names ${projName})
 endforeach()
 
 function(runtime_default_target)
-  cmake_parse_arguments(ARG "" "" "DEPENDS;PREFIXES" ${ARGN})
+  cmake_parse_arguments(ARG "" "" "DEPENDS;CMAKE_ARGS;PREFIXES" ${ARGN})
 
   include(${LLVM_BINARY_DIR}/runtimes/Components.cmake OPTIONAL)
   set(SUB_CHECK_TARGETS ${SUB_CHECK_TARGETS} PARENT_SCOPE)
   set_property(DIRECTORY APPEND PROPERTY CMAKE_CONFIGURE_DEPENDS ${LLVM_BINARY_DIR}/runtimes/Components.cmake)
 
   foreach(runtime_name ${runtime_names})
     list(APPEND extra_targets
       ${runtime_name}
llvm_ExternalProject_Add(runtimes
                                       -DLLVM_ENABLE_PROJECTS_USED=${LLVM_ENABLE_PROJECTS_USED}
                                       -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=${LLVM_ENABLE_PER_TARGET_RUNTIME_DIR}
                                       -DLLVM_BUILD_TOOLS=${LLVM_BUILD_TOOLS}
                                       -DCMAKE_C_COMPILER_WORKS=ON
                                       -DCMAKE_CXX_COMPILER_WORKS=ON
                                       -DCMAKE_ASM_COMPILER_WORKS=ON
                                       ${COMMON_CMAKE_ARGS}
                                       ${RUNTIMES_CMAKE_ARGS}
+                                      ${ARG_CMAKE_ARGS}
                            PASSTHROUGH_PREFIXES LLVM_ENABLE_RUNTIMES
                                                 LLVM_USE_LINKER
                                                 ${ARG_PREFIXES}
                            EXTRA_TARGETS ${extra_targets}
                                          ${test_targets}
                                          ${SUB_COMPONENTS}
                                          ${SUB_CHECK_TARGETS}
                                          ${SUB_INSTALL_TARGETS}
llvm_ExternalProject_Add(runtimes-${name}
                                       -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=${LLVM_ENABLE_PER_TARGET_RUNTIME_DIR}
                                       -DCMAKE_C_COMPILER_WORKS=ON
                                       -DCMAKE_CXX_COMPILER_WORKS=ON
                                       -DCMAKE_ASM_COMPILER_WORKS=ON
                                       -DCOMPILER_RT_DEFAULT_TARGET_ONLY=ON
                                       -DLLVM_RUNTIMES_TARGET=${name}
                                       ${COMMON_CMAKE_ARGS}
                                       ${${name}_extra_args}
                            EXTRA_TARGETS ${${name}_extra_targets}
                                          ${${name}_test_targets}
                            USE_TOOLCHAIN
                            TARGET_TRIPLE ${target}
                            ${EXTRA_ARGS})
 endfunction()
 
 if(runtimes)
   # Create a runtimes target that uses this file as its top-level CMake file.
   # The runtimes target is a configuration of all the runtime libraries
   # together in a single CMake invocation.
   set(extra_deps "")
   if("openmp" IN_LIST LLVM_ENABLE_RUNTIMES)
     if(TARGET opt)
       list(APPEND extra_deps opt)
     endif()
     if(TARGET llvm-link)
       list(APPEND extra_deps llvm-link)
     endif()
   endif()
+  if("libc" IN_LIST LLVM_ENABLE_RUNTIMES AND LLVM_LIBC_FULL_BUILD)
+    if(TARGET libc-hdrgen)
+      set(libc_tools libc-hdrgen)
+      set(libc_cmake_args "-DLIBC_HDRGEN_EXE=$<TARGET_FILE:libc-hdrgen>"
+                          "-DLLVM_LIBC_FULL_BUILD=ON")
+      list(APPEND extra_deps ${libc_tools})
+    else()
+      # We want to build the libc build tools before we can build the libc
+      # itself. So, the libc project should be included in LLVM_ENABLE_PROJECTS.
+      # This should have been done in llvm/CMakeLists.txt automatically when
+      # "libc" is detected in LLVM_ENABLE_RUNTIMES.
+      message(FATAL_ERROR "libc-hdrgen target missing unexpectedly")
+    endif()
+  endif()
   if(NOT LLVM_RUNTIME_TARGETS)
     runtime_default_target(
       DEPENDS ${builtins_dep} ${extra_deps}
+      CMAKE_ARGS ${libc_cmake_args}
       PREFIXES ${prefixes})
     set(test_targets check-runtimes)
   else()
     if("default" IN_LIST LLVM_RUNTIME_TARGETS)
       runtime_default_target(
         DEPENDS ${builtins_dep} ${extra_deps}
+        CMAKE_ARGS ${libc_cmake_args}
         PREFIXES ${prefixes})
       list(REMOVE_ITEM LLVM_RUNTIME_TARGETS "default")
     else()
       add_custom_target(runtimes)
       add_custom_target(runtimes-configure)
       add_custom_target(install-runtimes)
       add_custom_target(install-runtimes-stripped)
       if(LLVM_INCLUDE_TESTS)
foreach(name ${LLVM_RUNTIME_TARGETS})
       if(builtins_dep)
         if (LLVM_BUILTIN_TARGETS)
           set(builtins_dep_name "${builtins_dep}-${name}")
         else()
           set(builtins_dep_name ${builtins_dep})
         endif()
       endif()
       runtime_register_target(${name} ${name}
-        DEPENDS ${builtins_dep_name})
+        DEPENDS ${builtins_dep_name} ${libc_tools}
+        CMAKE_ARGS ${libc_cmake_args})
 
       add_dependencies(runtimes runtimes-${name})
       add_dependencies(runtimes-configure runtimes-${name}-configure)
       add_dependencies(install-runtimes install-runtimes-${name})
       add_dependencies(install-runtimes-stripped install-runtimes-${name}-stripped)
       if(LLVM_INCLUDE_TESTS)
         add_dependencies(check-runtimes check-runtimes-${name})
         add_dependencies(runtimes-test-depends runtimes-test-depends-${name})