[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, 4 insertions, 4 deletions

diff --git a/clang/unittests/Serialization/ForceCheckFileInputTest.cpp b/clang/unittests/Serialization/ForceCheckFileInputTest.cpp
index 16742a6..970eeef 100644
--- a/clang/unittests/Serialization/ForceCheckFileInputTest.cpp
+++ b/clang/unittests/Serialization/ForceCheckFileInputTest.cpp
@@ -66,9 +66,9 @@ export int aa = 43;
     CreateInvocationOptions CIOpts;
     CIOpts.VFS = llvm::vfs::createPhysicalFileSystem();
 
+    DiagnosticOptions DiagOpts;
     IntrusiveRefCntPtr<DiagnosticsEngine> Diags =
-        CompilerInstance::createDiagnostics(*CIOpts.VFS,
-                                            new DiagnosticOptions());
+        CompilerInstance::createDiagnostics(*CIOpts.VFS, DiagOpts);
     CIOpts.Diags = Diags;
 
     const char *Args[] = {"clang++",       "-std=c++20",
@@ -106,9 +106,9 @@ export int aa = 43;
   {
     CreateInvocationOptions CIOpts;
     CIOpts.VFS = llvm::vfs::createPhysicalFileSystem();
+    DiagnosticOptions DiagOpts;
     IntrusiveRefCntPtr<DiagnosticsEngine> Diags =
-        CompilerInstance::createDiagnostics(*CIOpts.VFS,
-                                            new DiagnosticOptions());
+        CompilerInstance::createDiagnostics(*CIOpts.VFS, DiagOpts);
     CIOpts.Diags = Diags;
 
     std::string BMIPath = llvm::Twine(TestDir + "/a.pcm").str();