[ScanDeps] ScanDeps shouldn't dependent on clangCodeGen

[ChuanqiXu9]

From #66462 (review), it shows that now clangDependencyScanning depends on clangCodeGen, which cause the size of clangd to be much larger.

I found the reason why clangDependencyScanning depends on clangCodeGen is that DependencyScanningWorker.cpp uses ObjectFilePCHContainerReader:

llvm-project/clang/lib/Tooling/DependencyScanning/DependencyScanningWorker.cpp

Lines 489 to 490 in b634e05

	PCHContainerOps->registerReader(
	std::make_unique<ObjectFilePCHContainerReader>());

It looks odd that clangDependencyScanning depends on clangCodeGen. Is there any chance to get rid of that?

CC: @Bigcheese @jansvoboda11 @benlangmuir @akyrtzi

[llvmbot]

@llvm/issue-subscribers-clang-modules

Author: Chuanqi Xu (ChuanqiXu9)

From https://github.com//pull/66462#pullrequestreview-2185579768, it shows that now `clangDependencyScanning` depends on `clangCodeGen`, which cause the size of clangd to be much larger.

I found the reason why clangDependencyScanning depends on clangCodeGen is that DependencyScanningWorker.cpp uses ObjectFilePCHContainerReader:

llvm-project/clang/lib/Tooling/DependencyScanning/DependencyScanningWorker.cpp

Lines 489 to 490 in b634e05

	PCHContainerOps->registerReader(
	std::make_unique<ObjectFilePCHContainerReader>());

I am not sure about the use case of wrapping PCMs inside an object file. But it looks indeed odd that clangDependencyScanning depends on clangCodeGen. Is there any chance to get rid of that?

CC: @Bigcheese @jansvoboda11 @benlangmuir @akyrtzi

[ChuanqiXu9]

It looks like clangDependencyScanning only depends on the class ObjectFilePCHContainerReader. And the implementation of ObjectFilePCHContainerReader only depends on LLVMObject. And clangDriver already depends on LLVMObject and clangDaemon depends on LLVMObject.

So if we can split ObjectFilePCHContainerReader from ObjectFilePCHContainerOperations.h and ObjectFilePCHContainerOperations.cpp, it looks like we get rid of clangCodeGen. Then clangd can get rid of redundant dependency and the clang-scan-deps can reduce its site too.

[llvmbot]

@llvm/issue-subscribers-clangd

Author: Chuanqi Xu (ChuanqiXu9)

From https://github.com//pull/66462#pullrequestreview-2185579768, it shows that now `clangDependencyScanning` depends on `clangCodeGen`, which cause the size of clangd to be much larger.

I found the reason why clangDependencyScanning depends on clangCodeGen is that DependencyScanningWorker.cpp uses ObjectFilePCHContainerReader:

llvm-project/clang/lib/Tooling/DependencyScanning/DependencyScanningWorker.cpp

Lines 489 to 490 in b634e05

	PCHContainerOps->registerReader(
	std::make_unique<ObjectFilePCHContainerReader>());

It looks odd that clangDependencyScanning depends on clangCodeGen. Is there any chance to get rid of that?

CC: @Bigcheese @jansvoboda11 @benlangmuir @akyrtzi

[jansvoboda11]

That sounds good to me!

[benlangmuir]

Agreed; if we can reduce binary size by splitting out the reader that makes sense to me.

[ChuanqiXu9]

Sent #99599