[LLVM][DWARF] Add support for monolithic types in .debug_names (#70515)

Enable Type Units with DWARF5 accelerator tables for monolithic DWARF.
Implementation relies on linker to tombstone offset in LocalTU list to
-1 when
it deduplciates type units using COMDAT.

Author: ayermolo

llvm/include/llvm/CodeGen/AccelTable.h

@@ -16,7 +16,6 @@
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/MapVector.h"
 #include "llvm/ADT/STLFunctionalExtras.h"
-#include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/BinaryFormat/Dwarf.h"
 #include "llvm/CodeGen/DIE.h"
@@ -104,8 +103,9 @@
 namespace llvm {
 
 class AsmPrinter;
-class DwarfCompileUnit;
+class DwarfUnit;
 class DwarfDebug;
+class DwarfTypeUnit;
 class MCSymbol;
 class raw_ostream;
 
@@ -197,6 +197,9 @@ template <typename DataT> class AccelTable : public AccelTableBase {
 
   template <typename... Types>
   void addName(DwarfStringPoolEntryRef Name, Types &&... Args);
+  void clear() { Entries.clear(); }
+  void addEntries(AccelTable<DataT> &Table);
+  const StringEntries getEntries() const { return Entries; }
 };
 
 template <typename AccelTableDataT>
@@ -250,11 +253,18 @@ class AppleAccelTableData : public AccelTableData {
 /// emitDWARF5AccelTable function.
 class DWARF5AccelTableData : public AccelTableData {
 public:
+  struct AttributeEncoding {
+    dwarf::Index Index;
+    dwarf::Form Form;
+  };
+
   static uint32_t hash(StringRef Name) { return caseFoldingDjbHash(Name); }
 
-  DWARF5AccelTableData(const DIE &Die, const DwarfCompileUnit &CU);
-  DWARF5AccelTableData(uint64_t DieOffset, unsigned DieTag, unsigned CUIndex)
-      : OffsetVal(DieOffset), DieTag(DieTag), UnitID(CUIndex) {}
+  DWARF5AccelTableData(const DIE &Die, const uint32_t UnitID,
+                       const bool IsTU = false);
+  DWARF5AccelTableData(const uint64_t DieOffset, const unsigned DieTag,
+                       const unsigned UnitID, const bool IsTU = false)
+      : OffsetVal(DieOffset), DieTag(DieTag), UnitID(UnitID), IsTU(IsTU) {}
 
 #ifndef NDEBUG
   void print(raw_ostream &OS) const override;
@@ -267,28 +277,66 @@ class DWARF5AccelTableData : public AccelTableData {
   }
   unsigned getDieTag() const { return DieTag; }
   unsigned getUnitID() const { return UnitID; }
+  bool isTU() const { return IsTU; }
   void normalizeDIEToOffset() {
     assert(std::holds_alternative<const DIE *>(OffsetVal) &&
            "Accessing offset after normalizing.");
     OffsetVal = std::get<const DIE *>(OffsetVal)->getOffset();
   }
+  bool isNormalized() const {
+    return std::holds_alternative<uint64_t>(OffsetVal);
+  }
 
 protected:
   std::variant<const DIE *, uint64_t> OffsetVal;
-  unsigned DieTag;
-  unsigned UnitID;
+  uint32_t DieTag : 16;
+  uint32_t UnitID : 15;
+  uint32_t IsTU : 1;
 
   uint64_t order() const override { return getDieOffset(); }
 };
 
+struct TypeUnitMetaInfo {
+  // Symbol for start of the TU section.
+  MCSymbol *Label;
+  // Unique ID of Type Unit.
+  unsigned UniqueID;
+};
+using TUVectorTy = SmallVector<TypeUnitMetaInfo, 1>;
 class DWARF5AccelTable : public AccelTable<DWARF5AccelTableData> {
+  // Symbols to start of all the TU sections that were generated.
+  TUVectorTy TUSymbols;
+
 public:
+  struct UnitIndexAndEncoding {
+    unsigned Index;
+    DWARF5AccelTableData::AttributeEncoding Endoding;
+  };
+  /// Returns type units that were constructed.
+  const TUVectorTy &getTypeUnitsSymbols() { return TUSymbols; }
+  /// Add a type unit start symbol.
+  void addTypeUnitSymbol(DwarfTypeUnit &U);
   /// Convert DIE entries to explicit offset.
   /// Needs to be called after DIE offsets are computed.
   void convertDieToOffset() {
     for (auto &Entry : Entries) {
       for (AccelTableData *Value : Entry.second.Values) {
-        static_cast<DWARF5AccelTableData *>(Value)->normalizeDIEToOffset();
+        DWARF5AccelTableData *Data = static_cast<DWARF5AccelTableData *>(Value);
+        // For TU we normalize as each Unit is emitted.
+        // So when this is invoked after CU construction we will be in mixed
+        // state.
+        if (!Data->isNormalized())
+          Data->normalizeDIEToOffset();
+      }
+    }
+  }
+
+  void addTypeEntries(DWARF5AccelTable &Table) {
+    for (auto &Entry : Table.getEntries()) {
+      for (AccelTableData *Value : Entry.second.Values) {
+        DWARF5AccelTableData *Data = static_cast<DWARF5AccelTableData *>(Value);
+        addName(Entry.second.Name, Data->getDieOffset(), Data->getDieTag(),
+                Data->getUnitID(), true);
       }
     }
   }
@@ -319,8 +367,9 @@ void emitDWARF5AccelTable(AsmPrinter *Asm, DWARF5AccelTable &Contents,
 void emitDWARF5AccelTable(
     AsmPrinter *Asm, DWARF5AccelTable &Contents,
     ArrayRef<std::variant<MCSymbol *, uint64_t>> CUs,
-    llvm::function_ref<unsigned(const DWARF5AccelTableData &)>
-        getCUIndexForEntry);
+    llvm::function_ref<std::optional<DWARF5AccelTable::UnitIndexAndEncoding>(
+        const DWARF5AccelTableData &)>
+        getIndexForEntry);
 
 /// Accelerator table data implementation for simple Apple accelerator tables
 /// with just a DIE reference.