[llvm] [DebugNames] Implement Entry::GetParentEntry query (PR #78760)

[Greg Clayton via llvm-commits]

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@@ -460,6 +460,16 @@ class DWARFDebugNames : public DWARFAcceleratorTable {
     /// Returns the Offset of the DIE within the containing CU or TU.
     std::optional<uint64_t> getDIEUnitOffset() const;
 
+    /// Returns true if this Entry has information about its parent DIE (i.e. if
+    /// it has an IDX_parent attribute)
+    bool hasParentInformation() const;
+
+    /// Returns the Entry corresponding to the parent of the DIE represented by
+    /// `this` Entry. If the parent is not in the table, nullopt is returned.
+    /// Precondition: hasParentInformation() == true.
+    /// An error is returned for ill-formed tables.
+    Expected<std::optional<DWARFDebugNames::Entry>> getParentDIEEntry() const;
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clayborg wrote:

Since we have the boolean that tell us if the entry has a parent index case, can we remove the need for an error if we get a `std::nullopt` back but `Entry::hasParentInformation() == true`? I do agree this is nice for `llvm-dwarfdump` to get an error back and display it. If we just use the error somewhere, then it is worth adding.

https://github.com/llvm/llvm-project/pull/78760