Improve type lookup using .debug_names parent chain (llvm#108907)

## Summary
This PR improves `SymbolFileDWARF::FindTypes()` by utilizing the newly
added parent chain `DW_IDX_parent` in `.debug_names`. The proposal was
originally discussed in [this
RFC](https://discourse.llvm.org/t/rfc-improve-dwarf-5-debug-names-type-lookup-parsing-speed/74151).

## Implementation
To leverage the parent chain for `SymbolFileDWARF::FindTypes()`, this PR
adds a new API: `GetTypesWithQuery` in `DWARFIndex` base class. The API
performs the same function as `GetTypes` with additional filtering using
`TypeQuery`. Since this only introduces filtering, the callback
mechanisms at all call sites remain unchanged. A default implementation
is given in `DWARFIndex` class which parses debug info and performs the
matching. In the `DebugNameDWARFIndex` override, the parent_contexts in
the `TypeQuery` is cross checked with parent chain in `.debug_names` for
for much faster filtering before fallback to base implementation for
final filtering.

Unlike the `GetFullyQualifiedType` API, which fully consumes the
`DW_IDX_parent` parent chain for exact matching, these new APIs perform
partial subset matching for type/namespace queries. This is necessary to
support queries involving anonymous or inline namespaces. For instance,
a user might request `NS1::NS2::NS3::Foo`, while the index table's
parent chain might contain `NS1::inline_NS2::NS3::Foo`, which would fail
exact matching.

## Performance Results
In one of our internal target using `.debug_names` + split dwarf.
Expanding a "this" pointer in locals view in VSCode:
94s => 48s. (Not sure why I got 94s this time instead of 70s last week).

---------

Co-authored-by: jeffreytan81 <jeffreytan@fb.com>

Author: 2 people

lldb/source/Plugins/SymbolFile/DWARF/DWARFIndex.cpp

@@ -126,3 +126,28 @@ bool DWARFIndex::GetFullyQualifiedTypeImpl(
     return callback(die);
   return true;
 }
+
+void DWARFIndex::GetTypesWithQuery(
+    TypeQuery &query, llvm::function_ref<bool(DWARFDIE die)> callback) {
+  GetTypes(query.GetTypeBasename(), [&](DWARFDIE die) {
+    return ProcessTypeDIEMatchQuery(query, die, callback);
+  });
+}
+
+bool DWARFIndex::ProcessTypeDIEMatchQuery(
+    TypeQuery &query, DWARFDIE die,
+    llvm::function_ref<bool(DWARFDIE die)> callback) {
+  // Nothing to match from query
+  if (query.GetContextRef().size() <= 1)
+    return callback(die);
+
+  std::vector<lldb_private::CompilerContext> die_context;
+  if (query.GetModuleSearch())
+    die_context = die.GetDeclContext();
+  else
+    die_context = die.GetTypeLookupContext();
+
+  if (!query.ContextMatches(die_context))
+    return true;
+  return callback(die);
+}

lldb/source/Plugins/SymbolFile/DWARF/DWARFIndex.h

@@ -64,6 +64,13 @@ class DWARFIndex {
   virtual void
   GetNamespaces(ConstString name,
                 llvm::function_ref<bool(DWARFDIE die)> callback) = 0;
+  /// Get type DIEs meeting requires of \a query.
+  /// in its decl parent chain as subset.  A base implementation is provided,
+  /// Specializations should override this if they are able to provide a faster
+  /// implementation.
+  virtual void
+  GetTypesWithQuery(TypeQuery &query,
+                    llvm::function_ref<bool(DWARFDIE die)> callback);
   virtual void
   GetFunctions(const Module::LookupInfo &lookup_info, SymbolFileDWARF &dwarf,
                const CompilerDeclContext &parent_decl_ctx,
@@ -115,6 +122,11 @@ class DWARFIndex {
   bool
   GetFullyQualifiedTypeImpl(const DWARFDeclContext &context, DWARFDIE die,
                             llvm::function_ref<bool(DWARFDIE die)> callback);
+
+  /// Check if the type \a die can meet the requirements of \a query.
+  bool
+  ProcessTypeDIEMatchQuery(TypeQuery &query, DWARFDIE die,
+                           llvm::function_ref<bool(DWARFDIE die)> callback);
 };
 } // namespace dwarf
 } // namespace lldb_private::plugin

lldb/source/Plugins/SymbolFile/DWARF/DebugNamesDWARFIndex.cpp

@@ -301,7 +301,8 @@ using Entry = llvm::DWARFDebugNames::Entry;
 /// If any parent does not have an `IDX_parent`, or the Entry data is corrupted,
 /// nullopt is returned.
 std::optional<llvm::SmallVector<Entry, 4>>
-getParentChain(Entry entry, uint32_t max_parents) {
+getParentChain(Entry entry,
+               uint32_t max_parents = std::numeric_limits<uint32_t>::max()) {
   llvm::SmallVector<Entry, 4> parent_entries;
 
   do {
@@ -374,6 +375,21 @@ void DebugNamesDWARFIndex::GetFullyQualifiedType(
   m_fallback.GetFullyQualifiedType(context, callback);
 }
 
+bool DebugNamesDWARFIndex::SameAsEntryContext(
+    const CompilerContext &query_context,
+    const DebugNames::Entry &entry) const {
+  // TODO: check dwarf tag matches.
+  // Peek at the AT_name of `entry` and test equality to `name`.
+  auto maybe_dieoffset = entry.getDIEUnitOffset();
+  if (!maybe_dieoffset)
+    return false;
+  DWARFUnit *unit = GetNonSkeletonUnit(entry);
+  if (!unit)
+    return false;
+  return query_context.name ==
+         unit->PeekDIEName(unit->GetOffset() + *maybe_dieoffset);
+}
+
 bool DebugNamesDWARFIndex::SameParentChain(
     llvm::ArrayRef<llvm::StringRef> parent_names,
     llvm::ArrayRef<DebugNames::Entry> parent_entries) const {
@@ -402,6 +418,45 @@ bool DebugNamesDWARFIndex::SameParentChain(
   return true;
 }
 
+bool DebugNamesDWARFIndex::SameParentChain(
+    llvm::ArrayRef<CompilerContext> parent_contexts,
+    llvm::ArrayRef<DebugNames::Entry> parent_entries) const {
+  if (parent_entries.size() != parent_contexts.size())
+    return false;
+
+  // If the AT_name of any parent fails to match the expected name, we don't
+  // have a match.
+  for (auto [parent_context, parent_entry] :
+       llvm::zip_equal(parent_contexts, parent_entries))
+    if (!SameAsEntryContext(parent_context, parent_entry))
+      return false;
+  return true;
+}
+
+bool DebugNamesDWARFIndex::WithinParentChain(
+    llvm::ArrayRef<CompilerContext> query_contexts,
+    llvm::ArrayRef<DebugNames::Entry> parent_chain) const {
+  if (query_contexts.size() == parent_chain.size())
+    return SameParentChain(query_contexts, parent_chain);
+
+  // If parent chain does not have enough entries, we can't possibly have a
+  // match.
+  while (!query_contexts.empty() &&
+         query_contexts.size() <= parent_chain.size()) {
+    if (SameAsEntryContext(query_contexts.front(), parent_chain.front())) {
+      query_contexts = query_contexts.drop_front();
+      parent_chain = parent_chain.drop_front();
+    } else {
+      // Name does not match, try next parent_chain entry if the current entry
+      // is namespace because the current one can be an inline namespace.
+      if (parent_chain.front().tag() != DW_TAG_namespace)
+        return false;
+      parent_chain = parent_chain.drop_front();
+    }
+  }
+  return query_contexts.empty();
+}
+
 void DebugNamesDWARFIndex::GetTypes(
     ConstString name, llvm::function_ref<bool(DWARFDIE die)> callback) {
   for (const DebugNames::Entry &entry :
@@ -444,6 +499,72 @@ void DebugNamesDWARFIndex::GetNamespaces(
   m_fallback.GetNamespaces(name, callback);
 }
 
+llvm::SmallVector<CompilerContext>
+DebugNamesDWARFIndex::GetTypeQueryParentContexts(TypeQuery &query) {
+  std::vector<lldb_private::CompilerContext> &query_decl_context =
+      query.GetContextRef();
+  llvm::SmallVector<CompilerContext> parent_contexts;
+  if (!query_decl_context.empty()) {
+    // Skip the last entry as it's the type we're matching parents for.
+    // Reverse the query decl context to match parent chain order.
+    llvm::ArrayRef<CompilerContext> parent_contexts_ref(
+        query_decl_context.data(), query_decl_context.size() - 1);
+    for (const CompilerContext &ctx : llvm::reverse(parent_contexts_ref)) {
+      // Skip any context without name because .debug_names might not encode
+      // them. (e.g. annonymous namespace)
+      if ((ctx.kind & CompilerContextKind::AnyType) !=
+              CompilerContextKind::Invalid &&
+          !ctx.name.IsEmpty())
+        parent_contexts.push_back(ctx);
+    }
+  }
+  return parent_contexts;
+}
+
+void DebugNamesDWARFIndex::GetTypesWithQuery(
+    TypeQuery &query, llvm::function_ref<bool(DWARFDIE die)> callback) {
+  ConstString name = query.GetTypeBasename();
+  std::vector<lldb_private::CompilerContext> query_context =
+      query.GetContextRef();
+  if (query_context.size() <= 1)
+    return GetTypes(name, callback);
+
+  llvm::SmallVector<CompilerContext> parent_contexts =
+      GetTypeQueryParentContexts(query);
+  // 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(name)) {
+    if (!isType(entry.tag()))
+      continue;
+
+    // If we get a NULL foreign_tu back, the entry doesn't match the type unit
+    // in the .dwp file, or we were not able to load the .dwo file or the DWO ID
+    // didn't match.
+    std::optional<DWARFTypeUnit *> foreign_tu = GetForeignTypeUnit(entry);
+    if (foreign_tu && foreign_tu.value() == nullptr)
+      continue;
+
+    std::optional<llvm::SmallVector<Entry, 4>> parent_chain =
+        getParentChain(entry);
+    if (!parent_chain) {
+      // Fallback: use the base class implementation.
+      if (!ProcessEntry(entry, [&](DWARFDIE die) {
+            return ProcessTypeDIEMatchQuery(query, die, callback);
+          }))
+        return;
+      continue;
+    }
+
+    if (WithinParentChain(parent_contexts, *parent_chain) &&
+        !ProcessEntry(entry, [&](DWARFDIE die) {
+          // After .debug_names filtering still sending to base class for
+          // further filtering before calling the callback.
+          return ProcessTypeDIEMatchQuery(query, die, callback);
+        }))
+      return;
+  }
+  m_fallback.GetTypesWithQuery(query, callback);
+}
+
 void DebugNamesDWARFIndex::GetFunctions(
     const Module::LookupInfo &lookup_info, SymbolFileDWARF &dwarf,
     const CompilerDeclContext &parent_decl_ctx,

lldb/source/Plugins/SymbolFile/DWARF/DebugNamesDWARFIndex.h

@@ -52,6 +52,10 @@ class DebugNamesDWARFIndex : public DWARFIndex {
                 llvm::function_ref<bool(DWARFDIE die)> callback) override;
   void GetNamespaces(ConstString name,
                      llvm::function_ref<bool(DWARFDIE die)> callback) override;
+  void
+  GetTypesWithQuery(TypeQuery &query,
+                    llvm::function_ref<bool(DWARFDIE die)> callback) override;
+
   void GetFunctions(const Module::LookupInfo &lookup_info,
                     SymbolFileDWARF &dwarf,
                     const CompilerDeclContext &parent_decl_ctx,
@@ -118,6 +122,36 @@ class DebugNamesDWARFIndex : public DWARFIndex {
   bool SameParentChain(llvm::ArrayRef<llvm::StringRef> parent_names,
                        llvm::ArrayRef<DebugNames::Entry> parent_entries) const;
 
+  bool SameParentChain(llvm::ArrayRef<CompilerContext> parent_contexts,
+                       llvm::ArrayRef<DebugNames::Entry> parent_entries) const;
+
+  /// Returns true if \a parent_contexts entries are within \a parent_chain.
+  /// This is diffferent from SameParentChain() which checks for exact match.
+  /// This function is required because \a parent_chain can contain inline
+  /// namespace entries which may not be specified in \a parent_contexts by
+  /// client.
+  ///
+  /// \param[in] parent_contexts
+  ///   The list of parent contexts to check for.
+  ///
+  /// \param[in] parent_chain
+  ///   The fully qualified parent chain entries from .debug_names index table
+  ///   to check against.
+  ///
+  /// \returns
+  ///   True if all \a parent_contexts entries are can be sequentially found
+  ///   inside
+  ///   \a parent_chain, otherwise False.
+  bool WithinParentChain(llvm::ArrayRef<CompilerContext> parent_contexts,
+                         llvm::ArrayRef<DebugNames::Entry> parent_chain) const;
+
+  /// Returns true if .debug_names pool entry \p entry matches \p query_context.
+  bool SameAsEntryContext(const CompilerContext &query_context,
+                          const DebugNames::Entry &entry) const;
+
+  llvm::SmallVector<CompilerContext>
+  GetTypeQueryParentContexts(TypeQuery &query);
+
   static void MaybeLogLookupError(llvm::Error error,
                                   const DebugNames::NameIndex &ni,
                                   llvm::StringRef name);

lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp

@@ -2748,8 +2748,9 @@ void SymbolFileDWARF::FindTypes(const TypeQuery &query, TypeResults &results) {
 
   std::lock_guard<std::recursive_mutex> guard(GetModuleMutex());
 
+  TypeQuery query_full(query);
   bool have_index_match = false;
-  m_index->GetTypes(type_basename, [&](DWARFDIE die) {
+  m_index->GetTypesWithQuery(query_full, [&](DWARFDIE die) {
     // Check the language, but only if we have a language filter.
     if (query.HasLanguage()) {
       if (!query.LanguageMatches(GetLanguageFamily(*die.GetCU())))
@@ -2813,7 +2814,7 @@ void SymbolFileDWARF::FindTypes(const TypeQuery &query, TypeResults &results) {
       auto type_basename_simple = query_simple.GetTypeBasename();
       // Copy our match's context and update the basename we are looking for
       // so we can use this only to compare the context correctly.
-      m_index->GetTypes(type_basename_simple, [&](DWARFDIE die) {
+      m_index->GetTypesWithQuery(query_simple, [&](DWARFDIE die) {
         // Check the language, but only if we have a language filter.
         if (query.HasLanguage()) {
           if (!query.LanguageMatches(GetLanguageFamily(*die.GetCU())))