Separate DIERef vs. user_id_t: GetForwardDeclClangTypeToDie()

[jankratochvil]

Summary

Reasons are the same as: D74637

[labath]

The thing I said on the other patch about DIERef vs user_id_t still applies. Let's continue the discussion there...

lldb/source/Plugins/SymbolFile/DWARF/DIERef.h

37

I'd very much like to avoid a default-constructed DIERef -- in the previous refactoring, I've deleted that concept and tried to use Optional<DIERef> in contexts, where the object can be empty.

[labath]

Per discussion on the other patch, I think this is fine too, just can we get rid of the DIERef default constructor? I think all you'd need is to use the insert DenseMap function instead of operator[].

[jankratochvil]

Sorry for that DenseMap::insert, I see it is the same as std::map, I should study DenseMap more.

[labath]

In D74690#1879121, @jankratochvil wrote:

Sorry for that DenseMap::insert, I see it is the same as std::map, I should study DenseMap more.

Yep, it tried to be similar to std::map, but there are some (sometimes subtle) differences.

lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp

1726

Actually, try_emplace would be slightly better here. (Sorry for the back-and-forth :/).

lldb/source/Plugins/SymbolFile/DWARF/DIERef.h

public:
 
   DIERef(llvm::Optional<uint32_t> dwo_num, Section section,
          dw_offset_t die_offset)
       : m_dwo_num(dwo_num.getValueOr(0)), m_dwo_num_valid(bool(dwo_num)),
         m_section(section), m_die_offset(die_offset) {
     assert(this->dwo_num() == dwo_num && "Dwo number out of range?");
   }
 
+  DIERef() {}
+
   llvm::Optional<uint32_t> dwo_num() const {
     if (m_dwo_num_valid)
       return m_dwo_num;
     return llvm::None;
   }
 
   Section section() const { return static_cast<Section>(m_section); }
 
   dw_offset_t die_offset() const { return m_die_offset; }
 
   bool operator<(DIERef other) const {
     if (m_dwo_num_valid != other.m_dwo_num_valid)
       return m_dwo_num_valid < other.m_dwo_num_valid;
     if (m_dwo_num_valid && (m_dwo_num != other.m_dwo_num))
       return m_dwo_num < other.m_dwo_num;
     if (m_section != other.m_section)
       return m_section < other.m_section;
     return m_die_offset < other.m_die_offset;
   }
 
 private:
   uint32_t m_dwo_num : 30;
   uint32_t m_dwo_num_valid : 1;
   uint32_t m_section : 1;
-  dw_offset_t m_die_offset;
+  dw_offset_t m_die_offset = DW_INVALID_OFFSET;
 };
 static_assert(sizeof(DIERef) == 8, "");
 
 typedef std::vector<DIERef> DIEArray;
 
 namespace llvm {
 template<> struct format_provider<DIERef> {
   static void format(const DIERef &ref, raw_ostream &OS, StringRef Style);
 };
 } // namespace llvm
 
 #endif // SymbolFileDWARF_DIERef_h_

lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp

if (!die.HasChildren()) {
              "Type already in the forward declaration map!");
       // Can't assume m_ast.GetSymbolFile() is actually a
       // SymbolFileDWARF, it can be a SymbolFileDWARFDebugMap for Apple
       // binaries.
       dwarf->GetForwardDeclDieToClangType()[die.GetDIE()] =
           clang_type.GetOpaqueQualType();
       dwarf->GetForwardDeclClangTypeToDie()
           [ClangUtil::RemoveFastQualifiers(clang_type).GetOpaqueQualType()] =
-          die.GetID();
+          *die.GetDIERef();
       m_ast.SetHasExternalStorage(clang_type.GetOpaqueQualType(), true);
     }
   }
 
   // If we made a clang type, set the trivial abi if applicable: We only
   // do this for pass by value - which implies the Trivial ABI. There
   // isn't a way to assert that something that would normally be pass by
   // value is pass by reference, so we ignore that attribute if set.

lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.h

 protected:
   typedef llvm::DenseMap<const DWARFDebugInfoEntry *, lldb_private::Type *>
       DIEToTypePtr;
   typedef llvm::DenseMap<const DWARFDebugInfoEntry *, lldb::VariableSP>
       DIEToVariableSP;
   typedef llvm::DenseMap<const DWARFDebugInfoEntry *,
                          lldb::opaque_compiler_type_t>
       DIEToClangType;
-  typedef llvm::DenseMap<lldb::opaque_compiler_type_t, lldb::user_id_t>
+  typedef llvm::DenseMap<lldb::opaque_compiler_type_t, DIERef>
       ClangTypeToDIE;
 
   DISALLOW_COPY_AND_ASSIGN(SymbolFileDWARF);
 
   virtual void LoadSectionData(lldb::SectionType sect_type,
                                lldb_private::DWARFDataExtractor &data);
 
   bool DeclContextMatchesThisSymbolFile(