Clean up unnecessary dependency

[dangyi]

Summary

The LINK_COMPONENTS dependency between DebugInfoCodeView and DebugInfoMSF is unnecessary. Breaking them would allow a more fine-controlled distribution.

[RKSimon]

Please can you ensure the diffs include context (git diff -U9999)

[MaskRay]

The llvm/lib/DebugInfo/CodeView/CMakeLists.txt change is fine. The change llvm/lib/MC/CMakeLists.txt is not.

Deleting a dependency needs to make sure the relevant components still (1) include what they use and (2) link what they use (the dependency for the direct include should be explicit specified).

(2) can be checked by making sure both -DBUILD_SHARED_LIBS=on and -DBUILD_SHARED_LIBS=off configurations still work. -DBUILD_SHARED_LIBS=on on Linux enables -Wl,-z,defs which requires every
shared object to have full direct dependencies specified (gold and ld.lld behavior; not in GNU ld). This makes for a more reliable build.

(1) is tricky to inspect. Bazel layering_check (-fmodule-name=X -fmodules-strict-decluse) can ensure an error: module X does not depend on a module exporting 'string.h' if a header file not mentioned by modulemap files is included.
MC actually includes DebugInfo/CodeView headers so the removal is not justified. Unfortunately the CMake -DLLVM_ENABLE_MODULES=on build does not specify -fmodule-name=X -fmodules-strict-decluse so this is difficult to enforce.

[dangyi]

Thank you for your detailed explanation. I thought LINK_COMPONENTS merely means, well, link dependency. I'll update the patch.

[MaskRay]

In D98465#2623030, @dangyi wrote:

Thank you for your detailed explanation. I thought LINK_COMPONENTS merely means, well, link dependency. I'll update the patch.

If somehow an inline function in a DebugInfo/CodeView header is moved to the associated .cpp file, a virtual function with non-vague-linkage vtable is needed, etc, the developer may have to add back the dependency.

If you don't have commit access, please provide your name and email https://llvm.org/docs/Phabricator.html#committing-someone-s-change-from-phabricator

llvm/lib/DebugInfo/CodeView/CMakeLists.txt

add_llvm_component_library(LLVMDebugInfoCodeView
   TypeStreamMerger.cpp
   TypeTableCollection.cpp
 
   ADDITIONAL_HEADER_DIRS
   ${LLVM_MAIN_INCLUDE_DIR}/llvm/DebugInfo/CodeView
 
   LINK_COMPONENTS
   Support
-  DebugInfoMSF
   )