[PATCH] D84127: Make LLVM_ENABLE_LTO function with multi-arch values for CMAKE_OSX_ARCHITECTURES

[Daniel Sanders via Phabricator via llvm-commits]

dsanders created this revision.
dsanders added a reviewer: bogner.
Herald added subscribers: dexonsmith, inglorion, aprantl, mgorny.
Herald added a reviewer: JDevlieghere.
Herald added a project: LLVM.

Each ld invocation within the clang command needs a unique filename on the
-object_path_lto option so that dsymutil can extract debug info for all compiled
slices. In the current code, every slice uses the same temporary filename and
as a result only one slice of debug info ends up in the dSYM.

clang already knows how to use -object_path_file and dsymutil for multiarch
builds correctly so use that method instead. There is however a strange quirk.
clang will only do this if there is at least one non-object in the command that
performs a link (this doesn't make sense in my opinion). To work around this
we include a nearly-empty file (empty causes warnings) in the linking clang
invocation.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D84127

Files:
  llvm/cmake/modules/AddLLVM.cmake


Index: llvm/cmake/modules/AddLLVM.cmake
===================================================================
--- llvm/cmake/modules/AddLLVM.cmake
+++ llvm/cmake/modules/AddLLVM.cmake
@@ -1970,27 +1970,33 @@
       set(file_ext dSYM)
     endif()
 
-    set(output_name "$<TARGET_FILE_NAME:${name}>.${file_ext}")
-
-    if(LLVM_EXTERNALIZE_DEBUGINFO_OUTPUT_DIR)
-      set(output_path "-o=${LLVM_EXTERNALIZE_DEBUGINFO_OUTPUT_DIR}/${output_name}")
-    else()
-      set(output_path "-o=${output_name}")
-    endif()
 
     if(CMAKE_CXX_FLAGS MATCHES "-flto"
       OR CMAKE_CXX_FLAGS_${uppercase_CMAKE_BUILD_TYPE} MATCHES "-flto")
 
-      set(lto_object ${CMAKE_CURRENT_BINARY_DIR}/${CMAKE_CFG_INTDIR}/${name}-lto.o)
+      # As long as we compile at least one file from source code, clang will
+      # invoke dsymutil on the temporary objects after lipo'ing all the slices
+      # together.
+      set(lto_src ${CMAKE_CURRENT_BINARY_DIR}/${CMAKE_CFG_INTDIR}/${name}-lto.cpp)
+      file(WRITE "${lto_src}" "extern int dummy;\n")
       set_property(TARGET ${name} APPEND_STRING PROPERTY
-        LINK_FLAGS " -Wl,-object_path_lto,${lto_object}")
+        LINK_FLAGS " ${lto_src}")
     endif()
-    if(NOT CMAKE_DSYMUTIL)
-      set(CMAKE_DSYMUTIL xcrun dsymutil)
+    if(LLVM_EXTERNALIZE_DEBUGINFO_OUTPUT_DIR)
+      set(output_name "$<TARGET_FILE_NAME:${name}>.${file_ext}")
+      set(output_path "${LLVM_EXTERNALIZE_DEBUGINFO_OUTPUT_DIR}/${output_name}")
+      add_custom_command(TARGET ${name} POST_BUILD
+        COMMAND ${CMAKE_COMMAND} -E make_directory "${LLVM_EXTERNALIZE_DEBUGINFO_OUTPUT_DIR}"
+        # Remove any old versions if present
+        COMMAND ${CMAKE_COMMAND} -E rm "-rf" "${output_path}"
+        # Move the dSYM clang emitted next to the output binary where we want it
+        # to be.
+        COMMAND ${CMAKE_COMMAND} -E rename "$<TARGET_FILE:${name}>.${file_ext}"
+                                           "${output_path}"
+      )
     endif()
     add_custom_command(TARGET ${name} POST_BUILD
-      COMMAND ${CMAKE_DSYMUTIL} ${output_path} $<TARGET_FILE:${name}>
-      ${strip_command}
+      COMMAND ${strip_command}
       )
   else()
     add_custom_command(TARGET ${name} POST_BUILD


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