[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, 6 insertions, 6 deletions

diff --git a/clang/lib/Frontend/FrontendAction.cpp b/clang/lib/Frontend/FrontendAction.cpp
index 54a2e3e..af9d18a 100644
--- a/clang/lib/Frontend/FrontendAction.cpp
+++ b/clang/lib/Frontend/FrontendAction.cpp
@@ -766,9 +766,8 @@ bool FrontendAction::BeginSourceFile(CompilerInstance &CI,
     IntrusiveRefCntPtr<DiagnosticsEngine> Diags(&CI.getDiagnostics());
 
     // The AST unit populates its own diagnostics engine rather than ours.
-    IntrusiveRefCntPtr<DiagnosticsEngine> ASTDiags(
-        new DiagnosticsEngine(Diags->getDiagnosticIDs(),
-                              &Diags->getDiagnosticOptions()));
+    IntrusiveRefCntPtr<DiagnosticsEngine> ASTDiags(new DiagnosticsEngine(
+        Diags->getDiagnosticIDs(), Diags->getDiagnosticOptions()));
     ASTDiags->setClient(Diags->getClient(), /*OwnsClient*/false);
 
     // FIXME: What if the input is a memory buffer?
@@ -776,7 +775,7 @@ bool FrontendAction::BeginSourceFile(CompilerInstance &CI,
 
     std::unique_ptr<ASTUnit> AST = ASTUnit::LoadFromASTFile(
         InputFile, CI.getPCHContainerReader(), ASTUnit::LoadPreprocessorOnly,
-        ASTDiags, CI.getFileSystemOpts(), CI.getHeaderSearchOpts());
+        nullptr, ASTDiags, CI.getFileSystemOpts(), CI.getHeaderSearchOpts());
     if (!AST)
       return false;
 
@@ -842,8 +841,9 @@ bool FrontendAction::BeginSourceFile(CompilerInstance &CI,
     StringRef InputFile = Input.getFile();
 
     std::unique_ptr<ASTUnit> AST = ASTUnit::LoadFromASTFile(
-        InputFile, CI.getPCHContainerReader(), ASTUnit::LoadEverything, Diags,
-        CI.getFileSystemOpts(), CI.getHeaderSearchOpts(), &CI.getLangOpts());
+        InputFile, CI.getPCHContainerReader(), ASTUnit::LoadEverything, nullptr,
+        Diags, CI.getFileSystemOpts(), CI.getHeaderSearchOpts(),
+        &CI.getLangOpts());
 
     if (!AST)
       return false;