[libc] Fix libc-hdrgen crosscompiling

[petrhosek]

The support introduced in 675702f356b0c3a540fa2e8af4192f7d658b2988 is not working correctly in all scenarios. Instead of setup_host_tool function, we can use the existing targets introduced by add_tablegen macro.

[llvmbot]

@llvm/pr-subscribers-libc

Author: Petr Hosek (petrhosek)

Changes

The support introduced in 675702f356b0c3a540fa2e8af4192f7d658b2988 is not working correctly in all scenarios. Instead of setup_host_tool function, we can use the existing targets introduced by add_tablegen macro.

---

Full diff: https://github.com/llvm/llvm-project/pull/78227.diff

3 Files Affected:

• (modified) libc/CMakeLists.txt (+4)
• (modified) libc/utils/HdrGen/CMakeLists.txt (-2)
• (modified) llvm/runtimes/CMakeLists.txt (+14-6)

diff --git a/libc/CMakeLists.txt b/libc/CMakeLists.txt
index 9c82db754b5f73..fd1f945455d8e2 100644
--- a/libc/CMakeLists.txt
+++ b/libc/CMakeLists.txt
@@ -34,6 +34,10 @@ if(LLVM_LIBC_FULL_BUILD OR LIBC_GPU_BUILD OR LIBC_GPU_ARCHITECTURES)
     # We need to set up hdrgen first since other targets depend on it.
     add_subdirectory(utils/LibcTableGenUtil)
     add_subdirectory(utils/HdrGen)
+    # Calling add_tablegen sets variables like LIBC_TABLEGEN_EXE in
+    # PARENT_SCOPE which get lost until saved in the cache.
+    set(LIBC_TABLEGEN_EXE "${LIBC_TABLEGEN_EXE}" CACHE INTERNAL "")
+    set(LIBC_TABLEGEN_TARGET "${LIBC_TABLEGEN_TARGET}" CACHE INTERNAL "")
   else()
     message(STATUS "Will use ${LIBC_HDRGEN_EXE} for libc header generation.")
   endif()
diff --git a/libc/utils/HdrGen/CMakeLists.txt b/libc/utils/HdrGen/CMakeLists.txt
index cfadd040df41e9..0ec1cba542d400 100644
--- a/libc/utils/HdrGen/CMakeLists.txt
+++ b/libc/utils/HdrGen/CMakeLists.txt
@@ -18,5 +18,3 @@ target_include_directories(libc-hdrgen PRIVATE ${LLVM_INCLUDE_DIR} ${LLVM_MAIN_I
 target_link_libraries(libc-hdrgen PRIVATE LibcTableGenUtil)
 
 add_subdirectory(PrototypeTestGen)
-
-setup_host_tool(libc-hdrgen LIBC_HDRGEN libc_hdrgen_exe libc_hdrgen_target)
diff --git a/llvm/runtimes/CMakeLists.txt b/llvm/runtimes/CMakeLists.txt
index a41945eb113b2f..8c48d85a4346f4 100644
--- a/llvm/runtimes/CMakeLists.txt
+++ b/llvm/runtimes/CMakeLists.txt
@@ -425,14 +425,22 @@ if(runtimes)
   endif()
   if("libc" IN_LIST LLVM_ENABLE_PROJECTS AND
       (LLVM_LIBC_FULL_BUILD OR LIBC_GPU_BUILD OR LIBC_GPU_ARCHITECTURES))
-    get_host_tool_path(libc-hdrgen LIBC_HDRGEN libc_hdrgen_exe libc_hdrgen_target)
-    if(NOT libc_hdrgen_exe)
+    if(LIBC_HDRGEN_EXE)
+      set(hdrgen_exe ${LIBC_HDRGEN_EXE})
+    else()
+      if(TARGET ${LIBC_TABLEGEN_EXE})
+        set(hdrgen_exe $<TARGET_FILE:${LIBC_TABLEGEN_EXE}>)
+      else()
+        set(hdrgen_exe ${LIBC_TABLEGEN_EXE})
+      endif()
+      set(hdrgen_deps ${LIBC_TABLEGEN_TARGET})
+    endif()
+    if(NOT hdrgen_exe)
       message(FATAL_ERROR "libc-hdrgen executable missing")
     endif()
-    set(libc_cmake_args "-DLIBC_HDRGEN_EXE=${libc_hdrgen_exe}"
+    set(libc_cmake_args "-DLIBC_HDRGEN_EXE=${hdrgen_exe}"
                         "-DLLVM_LIBC_FULL_BUILD=ON")
-    set(libc_tools libc_hdrgen_target)
-    list(APPEND extra_deps ${libc_hdrgen_target})
+    list(APPEND extra_deps ${hdrgen_deps})
     if(LIBC_GPU_BUILD OR LIBC_GPU_ARCHITECTURES)
       foreach(dep clang-offload-packager nvptx-arch amdgpu-arch)
         if(TARGET ${dep})
@@ -485,7 +493,7 @@ if(runtimes)
       check_apple_target(${name} runtime)
 
       runtime_register_target(${name}
-        DEPENDS ${builtins_dep_name} ${libc_tools}
+        DEPENDS ${builtins_dep_name} ${hdrgen_deps}
         CMAKE_ARGS -DLLVM_DEFAULT_TARGET_TRIPLE=${name} ${libc_cmake_args}
         EXTRA_ARGS TARGET_TRIPLE ${name})
     endforeach()

[jhuber6]

Fails with this locally.

[0/5] Building native libc-hdrgen...
ninja: error: unknown target 'libc-hdrgen'
FAILED: NATIVE/bin/libc-hdrgen /home/jhuber/Documents/llvm/llvm-project/build/NATIVE/bin/libc-hdrgen 
cd /home/jhuber/Documents/llvm/llvm-project/build/NATIVE && /usr/bin/cmake --build /home/jhuber/Documents/llvm/llvm-project/build/NATIVE --target libc-hdrgen --config Release
ninja: build stopped: subcommand failed.

My CMake is pretty close to the following, you could probably remove a lot of stuff.

cmake ../llvm -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_PROJECTS="clang;clang-tools-extra;compiler-rt;lld" -DLLVM_ENABLE_RUNTIMES="openmp;libc;libunwind" -DLLVM_ENABLE_ASSERTIONS=ON -DLIBOMPTARGET_ENABLE_DEBUG=ON -DLIBOMPTARGET_DEVICE_ARCHITECTURES="gfx1030;sm_60;sm_89" -DLLVM_USE_LINKER=lld -DCLANG_DEFAULT_LINKER=lld -DLIBC_GPU_ARCHITECTURES="sm_89;gfx1030" -DLIBC_GPU_TEST_JOBS=1 -DLLVM_OPTIMIZED_TABLEGEN=ON -DBUILD_SHARED_LIBS=ON -DLLVM_CCACHE_BUILD=ON -DLLVM_APPEND_VC_REV=OFF -G Ninja && ninja

[petrhosek]

I suspect it's related to -DLLVM_OPTIMIZED_TABLEGEN=ON but I cannot reproduce this locally using your CMake options, was this with clean or incremental build?

[jhuber6]

I suspect it's related to -DLLVM_OPTIMIZED_TABLEGEN=ON but I cannot reproduce this locally using your CMake options, was this with clean or incremental build?

I did a clean build and still got

[1475/6997] Building native libc-hdrgen...
ninja: error: unknown target 'libc-hdrgen'
[1494/6997] Creating library symlink lib/libLLVMCodeGenTypes.so
FAILED: NATIVE/bin/libc-hdrgen /home/jhuber/Documents/llvm/llvm-project/build/NATIVE/bin/libc-hdrgen 
cd /home/jhuber/Documents/llvm/llvm-project/build/NATIVE && /usr/bin/cmake --build /home/jhuber/Documents/llvm/llvm-project/build/NATIVE --target libc-hdrgen --config Release

Curious that you can't reproduce it, here's a script that I used originally https://gist.github.com/jhuber6/c439286bf0da51905649b334efac02ee.

[petrhosek]

Never mind, I can reproduce it now, I was too eager at dropping flags...

[petrhosek]

The issue you ran into should be addressed in the latest revision.

[jhuber6]

Thanks, fixed my issues.