[Lldb-commits] [lldb] Improve performance of .debug_names lookups when DW_IDX_parent attributes are used (PR #91808)

[Felipe de Azevedo Piovezan via lldb-commits]

felipepiovezan wrote:

Ok, minor correction: if there is no complete parent chain, it just defaults to the older implementation (which calls ProcessEntry). But my point still stands: I don't believe this is related to the presence of IDX_parent.

```
void DebugNamesDWARFIndex::GetFullyQualifiedType(
    const DWARFDeclContext &context,
    llvm::function_ref<bool(DWARFDIE die)> callback) {
  if (context.GetSize() == 0)
    return;

  llvm::StringRef leaf_name = context[0].name;
  llvm::SmallVector<llvm::StringRef> parent_names;
  for (auto idx : llvm::seq<int>(1, context.GetSize()))
    parent_names.emplace_back(context[idx].name);

  // For each entry, grab its parent chain and check if we have a match.
  for (const DebugNames::Entry &entry :
       m_debug_names_up->equal_range(leaf_name)) {
    if (!isType(entry.tag()))
      continue;

    // Grab at most one extra parent, subsequent parents are not necessary to
    // test equality.
    std::optional<llvm::SmallVector<Entry, 4>> parent_chain =
        getParentChain(entry, parent_names.size() + 1);

    if (!parent_chain) {
      // Fallback: use the base class implementation.
      if (!ProcessEntry(entry, [&](DWARFDIE die) {
            return GetFullyQualifiedTypeImpl(context, die, callback);
          }))
        return;
      continue;
    }

    if (SameParentChain(parent_names, *parent_chain) &&
        !ProcessEntry(entry, callback))
      return;
  }
}
```

https://github.com/llvm/llvm-project/pull/91808