[libc] Make crt1.o available to clang for GPU builds

[jhuber6]

Summary:
We want to provide the crt1.o object inside of the current build so
that other projects can use it for tests. Because it's currently an
object library (as is also required for the dependencies for the
hermetic tests) this cannot be renamed and is not emitted by default.
Here we simply add an executable that emits bitcode so that CMake will
give it a name.

[llvmbot]

@llvm/pr-subscribers-libc

Author: Joseph Huber (jhuber6)

Changes

Summary:
We want to provide the crt1.o object inside of the current build so
that other projects can use it for tests. Because it's currently an
object library (as is also required for the dependencies for the
hermetic tests) this cannot be renamed and is not emitted by default.
Here we simply add an executable that emits bitcode so that CMake will
give it a name.

---

Full diff: https://github.com/llvm/llvm-project/pull/100599.diff

1 Files Affected:

• (modified) libc/startup/gpu/CMakeLists.txt (+11)

diff --git a/libc/startup/gpu/CMakeLists.txt b/libc/startup/gpu/CMakeLists.txt
index 6f67fa9ff44f7..f1706c1a2e317 100644
--- a/libc/startup/gpu/CMakeLists.txt
+++ b/libc/startup/gpu/CMakeLists.txt
@@ -26,6 +26,16 @@ function(add_startup_object name)
     PROPERTIES
       OUTPUT_NAME ${name}.o
   )
+
+  # Make an executable target of relocatable bitcode for clang if needed.
+  if(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR)
+    add_executable(${fq_target_name}.exe $<TARGET_OBJECTS:${fq_target_name}>)
+    set_target_properties(${fq_target_name}.exe PROPERTIES
+      RUNTIME_OUTPUT_DIRECTORY ${LIBC_LIBRARY_DIR}
+      RUNTIME_OUTPUT_NAME ${name}.o)
+    target_link_options(${fq_target_name}.exe PRIVATE 
+                        "-flto" "-Wl,--lto-emit-llvm" "-march=sm_90")
+  endif()
 endfunction()
 
 if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_ARCHITECTURE})
@@ -44,6 +54,7 @@ set(startup_components crt1)
 foreach(target IN LISTS startup_components)
   set(fq_target_name libc.startup.gpu.${target})
   add_dependencies(libc-startup ${fq_target_name})
+
   install(FILES $<TARGET_OBJECTS:${fq_target_name}>
           DESTINATION ${LIBC_INSTALL_LIBRARY_DIR}
           RENAME $<TARGET_PROPERTY:${fq_target_name},OUTPUT_NAME>

[lntue]

Do you want to hard-code the -march here?

[jhuber6]

Yeah that's a hack, I can probably patch clang for it.

[jhuber6]

It pretty much just needs to be there to make clang happy, I'll just leave it blank for now.

[jhuber6]

I think I can use this trick to get the bitcode version as well without needing llvm-link.