[clang] [llvm] [clang][DebugInfo] Add symbol for debugger with VTable information. (PR #130255)

[Michael Buch via cfe-commits]

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@@ -2518,6 +2518,59 @@ StringRef CGDebugInfo::getVTableName(const CXXRecordDecl *RD) {
   return internString("_vptr$", RD->getNameAsString());
 }
 
+// Emit symbol for the debugger that points to the vtable address for
+// the given class. The symbol is named as '_vtable$'.
+// The debugger does not need to know any details about the contents of the
+// vtable as it can work this out using its knowledge of the ABI and the
+// existing information in the DWARF. The type is assumed to be 'void *'.
+void CGDebugInfo::emitVTableSymbol(llvm::GlobalVariable *VTable,
+                                   const CXXRecordDecl *RD) {
+  ASTContext &Context = CGM.getContext();
+  SmallString<64> Buffer;
+  Twine SymbolName = internString("_vtable$");
+  StringRef SymbolNameRef = SymbolName.toStringRef(Buffer);
+  DeclContext *DC = static_cast<DeclContext *>(const_cast<CXXRecordDecl *>(RD));
+  SourceLocation Loc;
+  QualType VoidPtr = Context.getPointerType(Context.VoidTy);
+
+  // We deal with two different contexts:
+  // - The type for the variable, which is part of the class that has the
+  //   vtable, is placed in the context of the DICompositeType metadata.
+  // - The DIGlobalVariable for the vtable is put in the DICompileUnitScope.
+
+  // The created non-member should be mark as 'artificial'. It will be
+  // placed it inside the scope of the C++ class/structure.
+  llvm::DIScope *DContext = getContextDescriptor(cast<Decl>(DC), TheCU);
+  auto *Ctxt = cast<llvm::DICompositeType>(DContext);
+  llvm::DIFile *Unit = getOrCreateFile(Loc);
+  llvm::DIType *VTy = getOrCreateType(VoidPtr, Unit);
+  llvm::DINode::DIFlags Flags = getAccessFlag(AccessSpecifier::AS_private, RD);
+  auto Tag = CGM.getCodeGenOpts().DwarfVersion >= 5
+                 ? llvm::dwarf::DW_TAG_variable
+                 : llvm::dwarf::DW_TAG_member;
+  llvm::DIDerivedType *OldDT = DBuilder.createStaticMemberType(
+      Ctxt, SymbolNameRef, Unit, /*LineNumber=*/0, VTy, Flags,
+      /*Val=*/nullptr, Tag);
+  llvm::DIDerivedType *DT =
+      static_cast<llvm::DIDerivedType *>(DBuilder.createArtificialType(OldDT));
----------------
Michael137 wrote:

Instead of calling `createArtificialType` could we just add `llvm::DINode::FlagArtificial` to the `Flags` parameter we pass to `createStaticMemberType`?

https://github.com/llvm/llvm-project/pull/130255