[llvm][DebugNames] Implement Entry::GetParentEntry query

Author: felipepiovezan

llvm/include/llvm/DebugInfo/DWARF/DWARFAcceleratorTable.h

@@ -460,6 +460,11 @@ class DWARFDebugNames : public DWARFAcceleratorTable {
     /// Returns the Offset of the DIE within the containing CU or TU.
     std::optional<uint64_t> getDIEUnitOffset() const;
 
+    /// Returns the Entry corresponding to the parent of the DIE represented by
+    /// `this` Entry. If the parent DIE is not indexed by this table, or if this
+    /// table does not track parents through IDX_parent, an error is returned.
+    Expected<DWARFDebugNames::Entry> getParentDIEEntry() const;
+
     /// Return the Abbreviation that can be used to interpret the raw values of
     /// this Accelerator Entry.
     const Abbrev &getAbbrev() const { return *Abbr; }
@@ -609,6 +614,13 @@ class DWARFDebugNames : public DWARFAcceleratorTable {
 
     Expected<Entry> getEntry(uint64_t *Offset) const;
 
+    // Returns the Entry at the relative `Offset` from the start of the Entry
+    // pool.
+    Expected<Entry> getEntryAtRelativeOffset(uint64_t Offset) const {
+      auto OffsetFromSection = Offset + this->EntriesBase;
+      return getEntry(&OffsetFromSection);
+    }
+
     /// Look up all entries in this Name Index matching \c Key.
     iterator_range<ValueIterator> equal_range(StringRef Key) const;
 

llvm/lib/DebugInfo/DWARF/DWARFAcceleratorTable.cpp

@@ -650,6 +650,16 @@ std::optional<uint64_t> DWARFDebugNames::Entry::getLocalTUIndex() const {
   return std::nullopt;
 }
 
+Expected<DWARFDebugNames::Entry>
+DWARFDebugNames::Entry::getParentDIEEntry() const {
+  // The offset of the accelerator table entry for the parent.
+  std::optional<DWARFFormValue> ParentEntryOff = lookup(dwarf::DW_IDX_parent);
+  if (!ParentEntryOff)
+    return createStringError(errc::illegal_byte_sequence,
+                             "Incorrectly terminated entry list.");
+  return NameIdx->getEntryAtRelativeOffset(ParentEntryOff->getRawUValue());
+}
+
 void DWARFDebugNames::Entry::dump(ScopedPrinter &W) const {
   W.startLine() << formatv("Abbrev: {0:x}\n", Abbr->Code);
   W.startLine() << formatv("Tag: {0}\n", Abbr->Tag);