[clang] Remove intrusive reference count from `DiagnosticOptions` (#139584)

The `DiagnosticOptions` class is currently intrusively
reference-counted, which makes reasoning about its lifetime very
difficult in some cases. For example, `CompilerInvocation` owns the
`DiagnosticOptions` instance (wrapped in `llvm::IntrusiveRefCntPtr`) and
only exposes an accessor returning `DiagnosticOptions &`. One would
think this gives `CompilerInvocation` exclusive ownership of the object,
but that's not the case:

```c++
void shareOwnership(CompilerInvocation &CI) {
  llvm::IntrusiveRefCntPtr<DiagnosticOptions> CoOwner = &CI.getDiagnosticOptions();
  // ...
}
```

This is a perfectly valid pattern that is being actually used in the
codebase.

I would like to ensure the ownership of `DiagnosticOptions` by
`CompilerInvocation` is guaranteed to be exclusive. This can be
leveraged for a copy-on-write optimization later on. This PR changes
usages of `DiagnosticOptions` across `clang`, `clang-tools-extra` and
`lldb` to not be intrusively reference-counted.

1 files changed, 2 insertions, 2 deletions

diff --git a/clang/lib/Frontend/ChainedIncludesSource.cpp b/clang/lib/Frontend/ChainedIncludesSource.cpp
index 95b0ed2..f9a398d 100644
--- a/clang/lib/Frontend/ChainedIncludesSource.cpp
+++ b/clang/lib/Frontend/ChainedIncludesSource.cpp
@@ -117,10 +117,10 @@ IntrusiveRefCntPtr<ExternalSemaSource> clang::createChainedIncludesSource(
     CInvok->getFrontendOpts().Inputs.push_back(InputFile);
 
     TextDiagnosticPrinter *DiagClient =
-      new TextDiagnosticPrinter(llvm::errs(), new DiagnosticOptions());
+        new TextDiagnosticPrinter(llvm::errs(), CI.getDiagnosticOpts());
     IntrusiveRefCntPtr<DiagnosticIDs> DiagID(new DiagnosticIDs());
     IntrusiveRefCntPtr<DiagnosticsEngine> Diags(
-        new DiagnosticsEngine(DiagID, &CI.getDiagnosticOpts(), DiagClient));
+        new DiagnosticsEngine(DiagID, CI.getDiagnosticOpts(), DiagClient));
 
     auto Clang = std::make_unique<CompilerInstance>(
         std::move(CInvok), CI.getPCHContainerOperations());