[BOLT][DWARF] Add support for transitive DW_AT_name/DW_AT_linkage_name resolution for DW_AT_name/DW_AT_linkage_name. (#119493)

This fix handles a case where a DIE that does not have
DW_AT_name/DW_AT_linkage_name, but has a reference to another DIE using
DW_AT_abstract_origin/DW_AT_specification. It also fixes a bug where
there are cross CU references for those attributes. Previously it would
use a DWARF Unit of a DIE which was being processed The
warf5-debug-names-cross-cu.s test just happened to work because how it
was constructed where string section was shared by both DWARF Units.

To resolve DW_AT_name/DW_AT_linkage_name this patch iterates over
references until it either reaches the final DIE or finds both of those
names.

Author: ayermolo

bolt/include/bolt/Core/DIEBuilder.h

@@ -162,7 +162,7 @@ class DIEBuilder {
 
   /// Clone an attribute in reference format.
   void cloneDieOffsetReferenceAttribute(
-      DIE &Die, const DWARFUnit &U, const DWARFDie &InputDIE,
+      DIE &Die, DWARFUnit &U, const DWARFDie &InputDIE,
       const DWARFAbbreviationDeclaration::AttributeSpec AttrSpec, uint64_t Ref);
 
   /// Clone an attribute in block format.

bolt/include/bolt/Core/DebugNames.h

@@ -72,8 +72,8 @@ class DWARF5AcceleratorTable {
     return std::move(FullTableBuffer);
   }
   /// Adds a DIE that is referenced across CUs.
-  void addCrossCUDie(const DIE *Die) {
-    CrossCUDies.insert({Die->getOffset(), Die});
+  void addCrossCUDie(DWARFUnit *Unit, const DIE *Die) {
+    CrossCUDies.insert({Die->getOffset(), {Unit, Die}});
   }
   /// Returns true if the DIE can generate an entry for a cross cu reference.
   /// This only checks TAGs of a DIE because when this is invoked DIE might not
@@ -145,7 +145,7 @@ class DWARF5AcceleratorTable {
   llvm::DenseMap<uint64_t, uint32_t> CUOffsetsToPatch;
   // Contains a map of Entry ID to Entry relative offset.
   llvm::DenseMap<uint64_t, uint32_t> EntryRelativeOffsets;
-  llvm::DenseMap<uint64_t, const DIE *> CrossCUDies;
+  llvm::DenseMap<uint64_t, std::pair<DWARFUnit *, const DIE *>> CrossCUDies;
   /// Adds Unit to either CUList, LocalTUList or ForeignTUList.
   /// Input Unit being processed, and DWO ID if Unit is being processed comes
   /// from a DWO section.
@@ -191,6 +191,29 @@ class DWARF5AcceleratorTable {
   void emitData();
   /// Emit augmentation string.
   void emitAugmentationString() const;
+  /// Creates a new entry for a given DIE.
+  std::optional<BOLTDWARF5AccelTableData *>
+  addEntry(DWARFUnit &DU, const DIE &CurrDie,
+           const std::optional<uint64_t> &DWOID,
+           const std::optional<BOLTDWARF5AccelTableData *> &Parent,
+           const std::optional<std::string> &Name,
+           const uint32_t NumberParentsInChain);
+  /// Returns UnitID for a given DWARFUnit.
+  uint32_t getUnitID(const DWARFUnit &Unit,
+                     const std::optional<uint64_t> &DWOID, bool &IsTU);
+  std::optional<std::string> getName(DWARFUnit &DU,
+                                     const std::optional<uint64_t> &DWOID,
+                                     const std::string &NameToUse,
+                                     DIEValue ValName);
+  /// Processes a DIE with references to other DIEs for DW_AT_name and
+  /// DW_AT_linkage_name resolution.
+  /// If DW_AT_name exists method creates a new entry for this DIE and returns
+  /// it.
+  std::optional<BOLTDWARF5AccelTableData *> processReferencedDie(
+      DWARFUnit &Unit, const DIE &Die, const std::optional<uint64_t> &DWOID,
+      const std::optional<BOLTDWARF5AccelTableData *> &Parent,
+      const std::string &NameToUse, const uint32_t NumberParentsInChain,
+      const dwarf::Attribute &Attr);
 };
 } // namespace bolt
 } // namespace llvm

bolt/lib/Core/DIEBuilder.cpp

@@ -622,7 +622,7 @@ DWARFDie DIEBuilder::resolveDIEReference(
 }
 
 void DIEBuilder::cloneDieOffsetReferenceAttribute(
-    DIE &Die, const DWARFUnit &U, const DWARFDie &InputDIE,
+    DIE &Die, DWARFUnit &U, const DWARFDie &InputDIE,
     const DWARFAbbreviationDeclaration::AttributeSpec AttrSpec, uint64_t Ref) {
   DIE *NewRefDie = nullptr;
   DWARFUnit *RefUnit = nullptr;
@@ -654,7 +654,7 @@ void DIEBuilder::cloneDieOffsetReferenceAttribute(
     // Adding referenced DIE to DebugNames to be used when entries are created
     // that contain cross cu references.
     if (DebugNamesTable.canGenerateEntryWithCrossCUReference(U, Die, AttrSpec))
-      DebugNamesTable.addCrossCUDie(DieInfo.Die);
+      DebugNamesTable.addCrossCUDie(&U, DieInfo.Die);
     // no matter forward reference or backward reference, we are supposed
     // to calculate them in `finish` due to the possible modification of
     // the DIE.