[clang] [llvm] [DebugInfo] Place local ODR-uniqued types in decl DISubprograms (PR #119001)

[Vladislav Dzhidzhoev via cfe-commits]

================
@@ -3901,6 +3903,57 @@ CGDebugInfo::getOrCreateLimitedType(const RecordType *Ty) {
   return Res;
 }
 
+llvm::DIScope *CGDebugInfo::PickCompositeTypeScope(llvm::DIScope *S,
+                                                   StringRef Identifier) {
+  using llvm::DISubprogram;
+
+  // Only adjust the scope for composite types placed into functions.
+  if (!isa<DISubprogram>(S))
+    return S;
+
+  // We must adjust the scope if the ODR-name of the type is set.
+  if (Identifier.empty())
+    return S;
+
+  // This type has an ODR-name, and might be de-duplicated during LTO. It needs
+  // to be placed in the unique declaration of the function, not a (potentially
+  // duplicated) definition.
+  DISubprogram *SP = cast<DISubprogram>(S);
+  if (DISubprogram *Decl = SP->getDeclaration())
+    return Decl;
+
+  // There is no declaration -- we must produce one and retrofit it to the
+  // existing definition. Assume that we can just harvest the existing
+  // information, clear the definition flag and set as decl.
+  DISubprogram::DISPFlags SPFlags = SP->getSPFlags();
+  SPFlags &= ~DISubprogram::SPFlagDefinition;
+
+  llvm::DINode::DIFlags Flags = SP->getFlags();
+  Flags &= ~llvm::DINode::FlagAllCallsDescribed;
+
+#ifdef EXPENSIVE_CHECKS
+  // If we're looking to be really rigorous and avoid a hard-to-debug mishap,
+  // make sure that there aren't any function definitions in the scope chain.
+  llvm::DIScope *ToCheck = SP->getScope();
+  do {
+    // We should terminate at a DIFile rather than a DICompileUnit -- we're
+    // not fully unique across LTO otherwise.
+    assert(!isa<llvm::DICompileUnit>(ToCheck));
+    if (auto *DISP = dyn_cast<DISubprogram>(ToCheck))
+      assert(!(DISP->getSPFlags() & DISubprogram::SPFlagDefinition));
+    ToCheck = ToCheck->getScope();
+  } while (ToCheck);
+#endif
+
+  DISubprogram *DeclSP = DBuilder.createFunction(
+      SP->getScope(), SP->getName(), SP->getLinkageName(), SP->getFile(),
+      SP->getLine(), SP->getType(), SP->getScopeLine(), Flags, SPFlags,
+      SP->getTemplateParams(), nullptr, nullptr, SP->getAnnotations());
----------------
dzhidzhoev wrote:

I've noticed that in the LLVM IR output of clang/test/CodeGenCXX/debug-info-local-types.cpp, `!DICompositeType(tag: DW_TAG_class_type, name: "bar"` is not attached to the retainedNodes of its scope (abstract DISubprogram for "foo").

Is it the desired behavior for us?

The reason is that DIBuilder::finalizeSubprogram() is never called for DeclSP. We could track it and finalize it in CGDebugInfo::finalize, or we could try something like this https://github.com/llvm/llvm-project/pull/139914.

https://github.com/llvm/llvm-project/pull/119001