CodeGen: Add a dwo output file argument to addPassesToEmitFile and hook it up to dwo output.

[pcc]

Summary

Part of PR37466.

Depends on D47051

[echristo]

One inline comment for discussion and LGTM.

-eric

llvm/lib/CodeGen/LLVMTargetMachine.cpp

199 ↗

(On Diff #147598)

I think the general output stream here at all is pretty awkward, but this isn't necessarily making it worse. Any ideas on where/how to clean this particular one up since you're in there right now? :)

[pcc]

llvm/lib/CodeGen/LLVMTargetMachine.cpp

199 ↗

(On Diff #147598)

One approach that I was thinking about was to move the MCObjectWriter creation into the TargetMachine client and have it be passed in as a parameter here. We could then also have things like MCAsmWriter and MCNullWriter which would let us drop the FileType enum as well. But for that to work we'd probably want to split the initialization of MCObjectWriter in two to allow the MCAsmBackend to set the MCObjectTargetWriter once it's created, which doesn't seem great but probably the lesser of two evils.

The MCObjectWriter part of this seems easy but getting it to work for the other output formats seemed a little trickier so I decided to leave it for now.

lib/CodeGen/BackendUtil.cpp

bool EmitAssemblyHelper::AddEmitPasses(legacy::PassManager &CodeGenPasses,
   TargetMachine::CodeGenFileType CGFT = getCodeGenFileType(Action);
 
   // Add ObjC ARC final-cleanup optimizations. This is done as part of the
   // "codegen" passes so that it isn't run multiple times when there is
   // inlining happening.
   if (CodeGenOpts.OptimizationLevel > 0)
     CodeGenPasses.add(createObjCARCContractPass());
 
-  if (TM->addPassesToEmitFile(CodeGenPasses, OS, CGFT,
+  if (TM->addPassesToEmitFile(CodeGenPasses, OS, nullptr, CGFT,
                               /*DisableVerify=*/!CodeGenOpts.VerifyModule)) {
     Diags.Report(diag::err_fe_unable_to_interface_with_target);
     return false;
   }
 
   return true;
 }