[lldb][DataFormatter] Simplify std::unordered_map::iterator formatter

[Michael137]

Depends on #97752

This patch changes the way we retrieve the key/value pair in the std::unordered_map::iterator formatter (similar to how we are changing it for std::map::iterator in #97713, the motivations being the same).

The old logic was not very easy to follow, and encoded the libc++ layout in non-obvious ways. But mainly it was also fragile to alignment miscalculations (#97443); this would break once the new layout of std::unordered_map landed as part of #93069.

Instead, this patch simply casts the __hash_iterator to a __node_pointer (which is what libc++ does too) and uses a straightforward GetChildMemberWithName("__value_") to get to the key/value we care about.

The std::unordered_map already does it this way, so we align the iterator counterpart to do the same. We can eventually re-use the core-part of the std::unordered_map and std::unordered_map::iterator formatters. But it will be an easier to change to review once both simplifications landed.

[llvmbot]

@llvm/pr-subscribers-lldb

Author: Michael Buch (Michael137)

Changes

Depends on #97752

This patch changes the way we retrieve the key/value pair in the std::unordered_map::iterator formatter (similar to how we are changing it for std::map::iterator in #97713, the motivations being the same).

The std::unordered_map already does it this way, so we align the iterator counterpart to do the same.

---

Full diff: https://github.com/llvm/llvm-project/pull/97754.diff

5 Files Affected:

• (modified) lldb/source/Plugins/Language/CPlusPlus/LibCxx.cpp (-149)
• (modified) lldb/source/Plugins/Language/CPlusPlus/LibCxx.h (+4-50)
• (modified) lldb/source/Plugins/Language/CPlusPlus/LibCxxUnorderedMap.cpp (+150)
• (modified) lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx/iterator/TestDataFormatterLibccIterator.py (+16)
• (modified) lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx/iterator/main.cpp (+19-6)

diff --git a/lldb/source/Plugins/Language/CPlusPlus/LibCxx.cpp b/lldb/source/Plugins/Language/CPlusPlus/LibCxx.cpp
index 05cfa0568c25d..feaa51a96843a 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/LibCxx.cpp
+++ b/lldb/source/Plugins/Language/CPlusPlus/LibCxx.cpp
@@ -202,155 +202,6 @@ bool lldb_private::formatters::LibcxxUniquePointerSummaryProvider(
   return true;
 }
 
-lldb_private::formatters::LibCxxUnorderedMapIteratorSyntheticFrontEnd::
-    LibCxxUnorderedMapIteratorSyntheticFrontEnd(lldb::ValueObjectSP valobj_sp)
-    : SyntheticChildrenFrontEnd(*valobj_sp) {
-  if (valobj_sp)
-    Update();
-}
-
-lldb::ChildCacheState lldb_private::formatters::
-    LibCxxUnorderedMapIteratorSyntheticFrontEnd::Update() {
-  m_pair_sp.reset();
-  m_iter_ptr = nullptr;
-
-  ValueObjectSP valobj_sp = m_backend.GetSP();
-  if (!valobj_sp)
-    return lldb::ChildCacheState::eRefetch;
-
-  TargetSP target_sp(valobj_sp->GetTargetSP());
-
-  if (!target_sp)
-    return lldb::ChildCacheState::eRefetch;
-
-  if (!valobj_sp)
-    return lldb::ChildCacheState::eRefetch;
-
-  auto exprPathOptions = ValueObject::GetValueForExpressionPathOptions()
-                             .DontCheckDotVsArrowSyntax()
-                             .SetSyntheticChildrenTraversal(
-                                 ValueObject::GetValueForExpressionPathOptions::
-                                     SyntheticChildrenTraversal::None);
-
-  // This must be a ValueObject* because it is a child of the ValueObject we
-  // are producing children for it if were a ValueObjectSP, we would end up
-  // with a loop (iterator -> synthetic -> child -> parent == iterator) and
-  // that would in turn leak memory by never allowing the ValueObjects to die
-  // and free their memory.
-  m_iter_ptr =
-      valobj_sp
-          ->GetValueForExpressionPath(".__i_.__node_", nullptr, nullptr,
-                                      exprPathOptions, nullptr)
-          .get();
-
-  if (m_iter_ptr) {
-    auto iter_child(valobj_sp->GetChildMemberWithName("__i_"));
-    if (!iter_child) {
-      m_iter_ptr = nullptr;
-      return lldb::ChildCacheState::eRefetch;
-    }
-
-    CompilerType node_type(iter_child->GetCompilerType()
-                               .GetTypeTemplateArgument(0)
-                               .GetPointeeType());
-
-    CompilerType pair_type(node_type.GetTypeTemplateArgument(0));
-
-    std::string name;
-    uint64_t bit_offset_ptr;
-    uint32_t bitfield_bit_size_ptr;
-    bool is_bitfield_ptr;
-
-    pair_type = pair_type.GetFieldAtIndex(
-        0, name, &bit_offset_ptr, &bitfield_bit_size_ptr, &is_bitfield_ptr);
-    if (!pair_type) {
-      m_iter_ptr = nullptr;
-      return lldb::ChildCacheState::eRefetch;
-    }
-
-    uint64_t addr = m_iter_ptr->GetValueAsUnsigned(LLDB_INVALID_ADDRESS);
-    m_iter_ptr = nullptr;
-
-    if (addr == 0 || addr == LLDB_INVALID_ADDRESS)
-      return lldb::ChildCacheState::eRefetch;
-
-    auto ts = pair_type.GetTypeSystem();
-    auto ast_ctx = ts.dyn_cast_or_null<TypeSystemClang>();
-    if (!ast_ctx)
-      return lldb::ChildCacheState::eRefetch;
-
-    // Mimick layout of std::__hash_iterator::__node_ and read it in
-    // from process memory.
-    //
-    // The following shows the contiguous block of memory:
-    //
-    //         +-----------------------------+ class __hash_node_base
-    // __node_ | __next_pointer __next_;     |
-    //         +-----------------------------+ class __hash_node
-    //         | size_t __hash_;             |
-    //         | __node_value_type __value_; | <<< our key/value pair
-    //         +-----------------------------+
-    //
-    CompilerType tree_node_type = ast_ctx->CreateStructForIdentifier(
-        llvm::StringRef(),
-        {{"__next_",
-          ast_ctx->GetBasicType(lldb::eBasicTypeVoid).GetPointerType()},
-         {"__hash_", ast_ctx->GetBasicType(lldb::eBasicTypeUnsignedLongLong)},
-         {"__value_", pair_type}});
-    std::optional<uint64_t> size = tree_node_type.GetByteSize(nullptr);
-    if (!size)
-      return lldb::ChildCacheState::eRefetch;
-    WritableDataBufferSP buffer_sp(new DataBufferHeap(*size, 0));
-    ProcessSP process_sp(target_sp->GetProcessSP());
-    Status error;
-    process_sp->ReadMemory(addr, buffer_sp->GetBytes(),
-                           buffer_sp->GetByteSize(), error);
-    if (error.Fail())
-      return lldb::ChildCacheState::eRefetch;
-    DataExtractor extractor(buffer_sp, process_sp->GetByteOrder(),
-                            process_sp->GetAddressByteSize());
-    auto pair_sp = CreateValueObjectFromData(
-        "pair", extractor, valobj_sp->GetExecutionContextRef(), tree_node_type);
-    if (pair_sp)
-      m_pair_sp = pair_sp->GetChildAtIndex(2);
-  }
-
-  return lldb::ChildCacheState::eRefetch;
-}
-
-llvm::Expected<uint32_t> lldb_private::formatters::
-    LibCxxUnorderedMapIteratorSyntheticFrontEnd::CalculateNumChildren() {
-  return 2;
-}
-
-lldb::ValueObjectSP lldb_private::formatters::
-    LibCxxUnorderedMapIteratorSyntheticFrontEnd::GetChildAtIndex(uint32_t idx) {
-  if (m_pair_sp)
-    return m_pair_sp->GetChildAtIndex(idx);
-  return lldb::ValueObjectSP();
-}
-
-bool lldb_private::formatters::LibCxxUnorderedMapIteratorSyntheticFrontEnd::
-    MightHaveChildren() {
-  return true;
-}
-
-size_t lldb_private::formatters::LibCxxUnorderedMapIteratorSyntheticFrontEnd::
-    GetIndexOfChildWithName(ConstString name) {
-  if (name == "first")
-    return 0;
-  if (name == "second")
-    return 1;
-  return UINT32_MAX;
-}
-
-SyntheticChildrenFrontEnd *
-lldb_private::formatters::LibCxxUnorderedMapIteratorSyntheticFrontEndCreator(
-    CXXSyntheticChildren *, lldb::ValueObjectSP valobj_sp) {
-  return (valobj_sp ? new LibCxxUnorderedMapIteratorSyntheticFrontEnd(valobj_sp)
-                    : nullptr);
-}
-
 /*
  (lldb) fr var ibeg --raw --ptr-depth 1 -T
  (std::__1::__wrap_iter<int *>) ibeg = {
diff --git a/lldb/source/Plugins/Language/CPlusPlus/LibCxx.h b/lldb/source/Plugins/Language/CPlusPlus/LibCxx.h
index 21dba015d1ba1..5307b5251ca84 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/LibCxx.h
+++ b/lldb/source/Plugins/Language/CPlusPlus/LibCxx.h
@@ -87,56 +87,6 @@ bool LibcxxContainerSummaryProvider(ValueObject &valobj, Stream &stream,
 bool LibcxxSpanSummaryProvider(ValueObject &valobj, Stream &stream,
                                const TypeSummaryOptions &options);
 
-/// Formats libcxx's std::unordered_map iterators
-///
-/// In raw form a std::unordered_map::iterator is represented as follows:
-///
-/// (lldb) var it --raw --ptr-depth 1
-/// (std::__1::__hash_map_iterator<
-///    std::__1::__hash_iterator<
-///      std::__1::__hash_node<
-///        std::__1::__hash_value_type<
-///            std::__1::basic_string<char, std::__1::char_traits<char>,
-///            std::__1::allocator<char> >, std::__1::basic_string<char,
-///            std::__1::char_traits<char>, std::__1::allocator<char> > >,
-///        void *> *> >)
-///  it = {
-///   __i_ = {
-///     __node_ = 0x0000600001700040 {
-///       __next_ = 0x0000600001704000
-///     }
-///   }
-/// }
-class LibCxxUnorderedMapIteratorSyntheticFrontEnd
-    : public SyntheticChildrenFrontEnd {
-public:
-  LibCxxUnorderedMapIteratorSyntheticFrontEnd(lldb::ValueObjectSP valobj_sp);
-
-  ~LibCxxUnorderedMapIteratorSyntheticFrontEnd() override = default;
-
-  llvm::Expected<uint32_t> CalculateNumChildren() override;
-
-  lldb::ValueObjectSP GetChildAtIndex(uint32_t idx) override;
-
-  lldb::ChildCacheState Update() override;
-
-  bool MightHaveChildren() override;
-
-  size_t GetIndexOfChildWithName(ConstString name) override;
-
-private:
-  ValueObject *m_iter_ptr = nullptr; ///< Held, not owned. Child of iterator
-                                     ///< ValueObject supplied at construction.
-
-  lldb::ValueObjectSP m_pair_sp; ///< ValueObject for the key/value pair
-                                 ///< that the iterator currently points
-                                 ///< to.
-};
-
-SyntheticChildrenFrontEnd *
-LibCxxUnorderedMapIteratorSyntheticFrontEndCreator(CXXSyntheticChildren *,
-                                                   lldb::ValueObjectSP);
-
 SyntheticChildrenFrontEnd *
 LibCxxVectorIteratorSyntheticFrontEndCreator(CXXSyntheticChildren *,
                                              lldb::ValueObjectSP);
@@ -230,6 +180,10 @@ SyntheticChildrenFrontEnd *
 LibcxxStdUnorderedMapSyntheticFrontEndCreator(CXXSyntheticChildren *,
                                               lldb::ValueObjectSP);
 
+SyntheticChildrenFrontEnd *
+LibCxxUnorderedMapIteratorSyntheticFrontEndCreator(CXXSyntheticChildren *,
+                                                   lldb::ValueObjectSP);
+
 SyntheticChildrenFrontEnd *
 LibcxxInitializerListSyntheticFrontEndCreator(CXXSyntheticChildren *,
                                               lldb::ValueObjectSP);
diff --git a/lldb/source/Plugins/Language/CPlusPlus/LibCxxUnorderedMap.cpp b/lldb/source/Plugins/Language/CPlusPlus/LibCxxUnorderedMap.cpp
index af29fdb6d0010..bfd8b648a6a46 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/LibCxxUnorderedMap.cpp
+++ b/lldb/source/Plugins/Language/CPlusPlus/LibCxxUnorderedMap.cpp
@@ -51,6 +51,50 @@ class LibcxxStdUnorderedMapSyntheticFrontEnd
   ValueObject *m_next_element = nullptr;
   std::vector<std::pair<ValueObject *, uint64_t>> m_elements_cache;
 };
+
+/// Formats libcxx's std::unordered_map iterators
+///
+/// In raw form a std::unordered_map::iterator is represented as follows:
+///
+/// (lldb) var it --raw --ptr-depth 1
+/// (std::__1::__hash_map_iterator<
+///    std::__1::__hash_iterator<
+///      std::__1::__hash_node<
+///        std::__1::__hash_value_type<
+///            std::__1::basic_string<char, std::__1::char_traits<char>,
+///            std::__1::allocator<char> >, std::__1::basic_string<char,
+///            std::__1::char_traits<char>, std::__1::allocator<char> > >,
+///        void *> *> >)
+///  it = {
+///   __i_ = {
+///     __node_ = 0x0000600001700040 {
+///       __next_ = 0x0000600001704000
+///     }
+///   }
+/// }
+class LibCxxUnorderedMapIteratorSyntheticFrontEnd
+    : public SyntheticChildrenFrontEnd {
+public:
+  LibCxxUnorderedMapIteratorSyntheticFrontEnd(lldb::ValueObjectSP valobj_sp);
+
+  ~LibCxxUnorderedMapIteratorSyntheticFrontEnd() override = default;
+
+  llvm::Expected<uint32_t> CalculateNumChildren() override;
+
+  lldb::ValueObjectSP GetChildAtIndex(uint32_t idx) override;
+
+  lldb::ChildCacheState Update() override;
+
+  bool MightHaveChildren() override;
+
+  size_t GetIndexOfChildWithName(ConstString name) override;
+
+private:
+  lldb::ValueObjectSP m_pair_sp; ///< ValueObject for the key/value pair
+                                 ///< that the iterator currently points
+                                 ///< to.
+};
+
 } // namespace formatters
 } // namespace lldb_private
 
@@ -246,3 +290,109 @@ lldb_private::formatters::LibcxxStdUnorderedMapSyntheticFrontEndCreator(
   return (valobj_sp ? new LibcxxStdUnorderedMapSyntheticFrontEnd(valobj_sp)
                     : nullptr);
 }
+
+lldb_private::formatters::LibCxxUnorderedMapIteratorSyntheticFrontEnd::
+    LibCxxUnorderedMapIteratorSyntheticFrontEnd(lldb::ValueObjectSP valobj_sp)
+    : SyntheticChildrenFrontEnd(*valobj_sp) {
+  if (valobj_sp)
+    Update();
+}
+
+lldb::ChildCacheState lldb_private::formatters::
+    LibCxxUnorderedMapIteratorSyntheticFrontEnd::Update() {
+  m_pair_sp.reset();
+
+  ValueObjectSP valobj_sp = m_backend.GetSP();
+  if (!valobj_sp)
+    return lldb::ChildCacheState::eRefetch;
+
+  TargetSP target_sp(valobj_sp->GetTargetSP());
+
+  if (!target_sp)
+    return lldb::ChildCacheState::eRefetch;
+
+  auto hash_iter_sp = valobj_sp->GetChildMemberWithName("__i_");
+  if (!hash_iter_sp)
+    return lldb::ChildCacheState::eRefetch;
+
+  auto hash_iter_type = hash_iter_sp->GetCompilerType();
+  if (!hash_iter_type.IsValid())
+    return lldb::ChildCacheState::eRefetch;
+
+  auto node_pointer_type = hash_iter_type.GetTypeTemplateArgument(0);
+  if (!node_pointer_type.IsValid())
+    return lldb::ChildCacheState::eRefetch;
+
+  auto hash_node_sp = hash_iter_sp->GetChildMemberWithName("__node_");
+  if (!hash_node_sp)
+    return lldb::ChildCacheState::eRefetch;
+
+  hash_node_sp = hash_iter_sp->Cast(node_pointer_type);
+  if (!hash_node_sp)
+    return lldb::ChildCacheState::eRefetch;
+
+  auto key_value_sp = hash_node_sp->GetChildMemberWithName("__value_");
+  if (!key_value_sp) {
+    key_value_sp = hash_node_sp->GetChildMemberWithName("__value_");
+    if (!key_value_sp) {
+      // clang-format off
+      // Since D101206 (ba79fb2e1f), libc++ wraps the `__value_` in an
+      // anonymous union.
+      // Child 0: __hash_node_base base class
+      // Child 1: __hash_
+      // Child 2: anonymous union
+      // clang-format on
+      auto anon_union_sp = hash_node_sp->GetChildAtIndex(2);
+      if (!anon_union_sp)
+        return lldb::ChildCacheState::eRefetch;
+
+      key_value_sp = anon_union_sp->GetChildMemberWithName("__value_");
+      if (!key_value_sp)
+        return lldb::ChildCacheState::eRefetch;
+    }
+  }
+
+  auto potential_child_sp = key_value_sp->Clone(ConstString("pair"));
+  if (potential_child_sp)
+    if (potential_child_sp->GetNumChildrenIgnoringErrors() == 1)
+      if (auto child0_sp = potential_child_sp->GetChildAtIndex(0);
+          child0_sp->GetName() == "__cc_" || child0_sp->GetName() == "__cc")
+        potential_child_sp = child0_sp->Clone(ConstString("pair"));
+
+  m_pair_sp = potential_child_sp;
+
+  return lldb::ChildCacheState::eRefetch;
+}
+
+llvm::Expected<uint32_t> lldb_private::formatters::
+    LibCxxUnorderedMapIteratorSyntheticFrontEnd::CalculateNumChildren() {
+  return 2;
+}
+
+lldb::ValueObjectSP lldb_private::formatters::
+    LibCxxUnorderedMapIteratorSyntheticFrontEnd::GetChildAtIndex(uint32_t idx) {
+  if (m_pair_sp)
+    return m_pair_sp->GetChildAtIndex(idx);
+  return lldb::ValueObjectSP();
+}
+
+bool lldb_private::formatters::LibCxxUnorderedMapIteratorSyntheticFrontEnd::
+    MightHaveChildren() {
+  return true;
+}
+
+size_t lldb_private::formatters::LibCxxUnorderedMapIteratorSyntheticFrontEnd::
+    GetIndexOfChildWithName(ConstString name) {
+  if (name == "first")
+    return 0;
+  if (name == "second")
+    return 1;
+  return UINT32_MAX;
+}
+
+SyntheticChildrenFrontEnd *
+lldb_private::formatters::LibCxxUnorderedMapIteratorSyntheticFrontEndCreator(
+    CXXSyntheticChildren *, lldb::ValueObjectSP valobj_sp) {
+  return (valobj_sp ? new LibCxxUnorderedMapIteratorSyntheticFrontEnd(valobj_sp)
+                    : nullptr);
+}
diff --git a/lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx/iterator/TestDataFormatterLibccIterator.py b/lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx/iterator/TestDataFormatterLibccIterator.py
index d9e316b9b8f4e..efd7128cd6ac7 100644
--- a/lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx/iterator/TestDataFormatterLibccIterator.py
+++ b/lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx/iterator/TestDataFormatterLibccIterator.py
@@ -59,3 +59,19 @@ def cleanup():
 
         self.expect("frame variable svI", substrs=['item = "hello"'])
         self.expect("expr svI", substrs=['item = "hello"'])
+
+        self.expect("frame variable iiumI", substrs=["first = 61453", "second = 51966"])
+        self.expect("expr iiumI", substrs=["first = 61453", "second = 51966"])
+
+        self.expect("frame variable siumI", substrs=['first = "hello"', "second = 137"])
+        self.expect("expr siumI", substrs=['first = "hello"', "second = 137"])
+
+        self.expect("frame variable iiumI.first", substrs=["first = 61453"])
+        self.expect("frame variable iiumI.first", substrs=["second"], matching=False)
+        self.expect("frame variable iiumI.second", substrs=["second = 51966"])
+        self.expect("frame variable iiumI.second", substrs=["first"], matching=False)
+
+        self.expect("frame variable siumI.first", substrs=['first = "hello"'])
+        self.expect("frame variable siumI.first", substrs=["second"], matching=False)
+        self.expect("frame variable siumI.second", substrs=["second = 137"])
+        self.expect("frame variable siumI.second", substrs=["first"], matching=False)
diff --git a/lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx/iterator/main.cpp b/lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx/iterator/main.cpp
index 9d1cbfd912868..534a22f98ffb8 100644
--- a/lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx/iterator/main.cpp
+++ b/lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx/iterator/main.cpp
@@ -5,11 +5,16 @@
 typedef std::map<int, int> intint_map;
 typedef std::map<std::string, int> strint_map;
 
+typedef std::unordered_map<int, int> intint_umap;
+typedef std::unordered_map<std::string, int> strint_umap;
+
 typedef std::vector<int> int_vector;
 typedef std::vector<std::string> string_vector;
 
-typedef intint_map::iterator iimter;
-typedef strint_map::iterator simter;
+typedef intint_map::iterator ii_map_iter;
+typedef strint_map::iterator si_map_iter;
+typedef intint_umap::iterator ii_umap_iter;
+typedef strint_umap::iterator si_umap_iter;
 
 typedef int_vector::iterator ivter;
 typedef string_vector::iterator svter;
@@ -22,16 +27,24 @@ int main()
 	strint_map sim;
 	sim["world"] = 42;
 
-	int_vector iv;
+        intint_umap iium;
+        iium[0xF00D] = 0xCAFE;
+
+        strint_umap sium;
+        sium["hello"] = 137;
+
+        int_vector iv;
 	iv.push_back(3);
 
 	string_vector sv;
 	sv.push_back("hello");
 
-	iimter iimI = iim.begin();
-	simter simI = sim.begin();
+        ii_map_iter iimI = iim.begin();
+        si_map_iter simI = sim.begin();
+        ii_umap_iter iiumI = iium.begin();
+        si_umap_iter siumI = sium.begin();
 
-	ivter ivI = iv.begin();
+        ivter ivI = iv.begin();
 	svter svI = sv.begin();
 
 	return 0; // Set break point at this line.

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[labath]

remove extra //