[lldb][DataFormatters] Support newer _LIBCPP_COMPRESSED_PAIR layout (#155153)

Starting with #154686 the
compressed_pair children are now wrapped in an anonymous structure.

This patch adjusts the LLDB data-formatters to support that.

Outstanding questions:
1. Should GetChildMemberWithName look through anonymous structures? That
will break users most likely. But maybe introducing a new API is worth
it? Then we wouldnt have to do this awkward passing around of
`anon_struct_index`
2. Do we support the layout without the anonymous structure? It's not
too much added complexity. And we did release that version of libc++, so
there is code out there compiled against it. But there is no great way
of testing it (some of our macOS matrix bots do test it i suppose, but
not in a targeted way). We have the layout "simulator" tests for some of
the STL types which I will adjust.

Author: Michael137

lldb/packages/Python/lldbsuite/test/make/libcxx-simulators-common/compressed_pair.h

@@ -8,7 +8,9 @@
 // 0 -> Post-c88580c layout
 // 1 -> Post-27c83382d83dc layout
 // 2 -> Post-769c42f4a552a layout
-// 3 -> padding-less no_unique_address-based layout (introduced in 27c83382d83dc)
+// 3 -> Post-f5e687d7bf49c layout
+// 4 -> padding-less no_unique_address-based layout (introduced in
+// 27c83382d83dc)
 
 namespace std {
 namespace __lldb {
@@ -42,7 +44,7 @@ template <class _ToPad> class __compressed_pair_padding {
                       ? 0
                       : sizeof(_ToPad) - __datasizeof_v<_ToPad>];
 };
-#elif COMPRESSED_PAIR_REV > 1 && COMPRESSED_PAIR_REV < 3
+#elif COMPRESSED_PAIR_REV > 1 && COMPRESSED_PAIR_REV < 4
 template <class _ToPad>
 inline const bool __is_reference_or_unpadded_object =
     (std::is_empty<_ToPad>::value && !__lldb_is_final<_ToPad>::value) ||
@@ -125,6 +127,27 @@ class __compressed_pair : private __compressed_pair_elem<_T1, 0>,
   _LLDB_NO_UNIQUE_ADDRESS T3 Initializer3;                                     \
   _LLDB_NO_UNIQUE_ADDRESS __compressed_pair_padding<T3> __padding3_;
 #elif COMPRESSED_PAIR_REV == 3
+#define _LLDB_COMPRESSED_PAIR(T1, Initializer1, T2, Initializer2)              \
+  struct {                                                                     \
+    [[__gnu__::__aligned__(                                                    \
+        alignof(T2))]] _LLDB_NO_UNIQUE_ADDRESS T1 Initializer1;                \
+    _LLDB_NO_UNIQUE_ADDRESS __compressed_pair_padding<T1> __padding1_;         \
+    _LLDB_NO_UNIQUE_ADDRESS T2 Initializer2;                                   \
+    _LLDB_NO_UNIQUE_ADDRESS __compressed_pair_padding<T2> __padding2_;         \
+  }
+
+#define _LLDB_COMPRESSED_TRIPLE(T1, Initializer1, T2, Initializer2, T3,        \
+                                Initializer3)                                  \
+  struct {                                                                     \
+    [[using __gnu__: __aligned__(alignof(T2)),                                 \
+      __aligned__(alignof(T3))]] _LLDB_NO_UNIQUE_ADDRESS T1 Initializer1;      \
+    _LLDB_NO_UNIQUE_ADDRESS __compressed_pair_padding<T1> __padding1_;         \
+    _LLDB_NO_UNIQUE_ADDRESS T2 Initializer2;                                   \
+    _LLDB_NO_UNIQUE_ADDRESS __compressed_pair_padding<T2> __padding2_;         \
+    _LLDB_NO_UNIQUE_ADDRESS T3 Initializer3;                                   \
+    _LLDB_NO_UNIQUE_ADDRESS __compressed_pair_padding<T3> __padding3_;         \
+  }
+#elif COMPRESSED_PAIR_REV == 4
 #define _LLDB_COMPRESSED_PAIR(T1, Name1, T2, Name2)                            \
   _LLDB_NO_UNIQUE_ADDRESS T1 Name1;                                            \
   _LLDB_NO_UNIQUE_ADDRESS T2 Name2

lldb/source/Plugins/Language/CPlusPlus/GenericList.cpp

@@ -339,11 +339,18 @@ lldb::ChildCacheState LibCxxForwardListFrontEnd::Update() {
   if (err.Fail() || !backend_addr)
     return lldb::ChildCacheState::eRefetch;
 
-  ValueObjectSP impl_sp(m_backend.GetChildMemberWithName("__before_begin_"));
+  auto list_base_sp = m_backend.GetChildAtIndex(0);
+  if (!list_base_sp)
+    return lldb::ChildCacheState::eRefetch;
+
+  // Anonymous strucutre index is in base class at index 0.
+  auto [impl_sp, is_compressed_pair] =
+      GetValueOrOldCompressedPair(*list_base_sp, /*anon_struct_idx=*/0,
+                                  "__before_begin_", "__before_begin_");
   if (!impl_sp)
     return ChildCacheState::eRefetch;
 
-  if (isOldCompressedPairLayout(*impl_sp))
+  if (is_compressed_pair)
     impl_sp = GetFirstValueOfLibCXXCompressedPair(*impl_sp);
 
   if (!impl_sp)
@@ -366,17 +373,10 @@ llvm::Expected<uint32_t> LibCxxListFrontEnd::CalculateNumChildren() {
   if (!m_head || !m_tail || m_node_address == 0)
     return 0;
 
-  ValueObjectSP size_node_sp(m_backend.GetChildMemberWithName("__size_"));
-  if (!size_node_sp) {
-    size_node_sp = m_backend.GetChildMemberWithName(
-        "__size_alloc_"); // pre-compressed_pair rework
-
-    if (!isOldCompressedPairLayout(*size_node_sp))
-      return llvm::createStringError("Unexpected std::list layout: expected "
-                                     "old __compressed_pair layout.");
-
+  auto [size_node_sp, is_compressed_pair] = GetValueOrOldCompressedPair(
+      m_backend, /*anon_struct_idx=*/1, "__size_", "__size_alloc_");
+  if (is_compressed_pair)
     size_node_sp = GetFirstValueOfLibCXXCompressedPair(*size_node_sp);
-  }
 
   if (size_node_sp)
     m_count = size_node_sp->GetValueAsUnsigned(UINT32_MAX);

lldb/source/Plugins/Language/CPlusPlus/LibCxx.cpp

@@ -49,11 +49,6 @@ static void consumeInlineNamespace(llvm::StringRef &name) {
   }
 }
 
-bool lldb_private::formatters::isOldCompressedPairLayout(
-    ValueObject &pair_obj) {
-  return isStdTemplate(pair_obj.GetTypeName(), "__compressed_pair");
-}
-
 bool lldb_private::formatters::isStdTemplate(ConstString type_name,
                                              llvm::StringRef type) {
   llvm::StringRef name = type_name.GetStringRef();
@@ -105,6 +100,44 @@ lldb_private::formatters::GetSecondValueOfLibCXXCompressedPair(
   return value;
 }
 
+std::pair<lldb::ValueObjectSP, bool>
+lldb_private::formatters::GetValueOrOldCompressedPair(
+    ValueObject &obj, size_t anon_struct_idx, llvm::StringRef child_name,
+    llvm::StringRef compressed_pair_name) {
+  auto is_old_compressed_pair = [](ValueObject &pair_obj) -> bool {
+    return isStdTemplate(pair_obj.GetTypeName(), "__compressed_pair");
+  };
+
+  // Try searching the child member in an anonymous structure first.
+  if (auto unwrapped = obj.GetChildAtIndex(anon_struct_idx)) {
+    ValueObjectSP node_sp(obj.GetChildMemberWithName(child_name));
+    if (node_sp)
+      return {node_sp, is_old_compressed_pair(*node_sp)};
+  }
+
+  // Older versions of libc++ don't wrap the children in anonymous structures.
+  // Try that instead.
+  ValueObjectSP node_sp(obj.GetChildMemberWithName(child_name));
+  if (node_sp)
+    return {node_sp, is_old_compressed_pair(*node_sp)};
+
+  // Try the even older __compressed_pair layout.
+
+  assert(!compressed_pair_name.empty());
+
+  node_sp = obj.GetChildMemberWithName(compressed_pair_name);
+
+  // Unrecognized layout (possibly older than LLDB supports).
+  if (!node_sp)
+    return {nullptr, false};
+
+  // Expected old compressed_pair layout, but got something else.
+  if (!is_old_compressed_pair(*node_sp))
+    return {nullptr, false};
+
+  return {node_sp, true};
+}
+
 bool lldb_private::formatters::LibcxxFunctionSummaryProvider(
     ValueObject &valobj, Stream &stream, const TypeSummaryOptions &options) {
 
@@ -205,11 +238,12 @@ bool lldb_private::formatters::LibcxxUniquePointerSummaryProvider(
   if (!valobj_sp)
     return false;
 
-  ValueObjectSP ptr_sp(valobj_sp->GetChildMemberWithName("__ptr_"));
+  auto [ptr_sp, is_compressed_pair] = GetValueOrOldCompressedPair(
+      *valobj_sp, /*anon_struct_idx=*/0, "__ptr_", "__ptr_");
   if (!ptr_sp)
     return false;
 
-  if (isOldCompressedPairLayout(*ptr_sp))
+  if (is_compressed_pair)
     ptr_sp = GetFirstValueOfLibCXXCompressedPair(*ptr_sp);
 
   if (!ptr_sp)
@@ -379,13 +413,14 @@ lldb_private::formatters::LibcxxUniquePtrSyntheticFrontEnd::Update() {
   if (!valobj_sp)
     return lldb::ChildCacheState::eRefetch;
 
-  ValueObjectSP ptr_sp(valobj_sp->GetChildMemberWithName("__ptr_"));
+  auto [ptr_sp, is_compressed_pair] = GetValueOrOldCompressedPair(
+      *valobj_sp, /*anon_struct_idx=*/0, "__ptr_", "__ptr_");
   if (!ptr_sp)
     return lldb::ChildCacheState::eRefetch;
 
   // Retrieve the actual pointer and the deleter, and clone them to give them
   // user-friendly names.
-  if (isOldCompressedPairLayout(*ptr_sp)) {
+  if (is_compressed_pair) {
     if (ValueObjectSP value_pointer_sp =
             GetFirstValueOfLibCXXCompressedPair(*ptr_sp))
       m_value_ptr_sp = value_pointer_sp->Clone(ConstString("pointer"));
@@ -424,17 +459,15 @@ enum class StringLayout { CSD, DSC };
 }
 
 static ValueObjectSP ExtractLibCxxStringData(ValueObject &valobj) {
-  if (auto rep_sp = valobj.GetChildMemberWithName("__rep_"))
-    return rep_sp;
-
-  ValueObjectSP valobj_r_sp = valobj.GetChildMemberWithName("__r_");
-  if (!valobj_r_sp || !valobj_r_sp->GetError().Success())
+  auto [valobj_r_sp, is_compressed_pair] = GetValueOrOldCompressedPair(
+      valobj, /*anon_struct_idx=*/0, "__rep_", "__r_");
+  if (!valobj_r_sp)
     return nullptr;
 
-  if (!isOldCompressedPairLayout(*valobj_r_sp))
-    return nullptr;
+  if (is_compressed_pair)
+    return GetFirstValueOfLibCXXCompressedPair(*valobj_r_sp);
 
-  return GetFirstValueOfLibCXXCompressedPair(*valobj_r_sp);
+  return valobj_r_sp;
 }
 
 /// Determine the size in bytes of \p valobj (a libc++ std::string object) and

lldb/source/Plugins/Language/CPlusPlus/LibCxx.h

@@ -25,7 +25,22 @@ GetChildMemberWithName(ValueObject &obj,
 
 lldb::ValueObjectSP GetFirstValueOfLibCXXCompressedPair(ValueObject &pair);
 lldb::ValueObjectSP GetSecondValueOfLibCXXCompressedPair(ValueObject &pair);
-bool isOldCompressedPairLayout(ValueObject &pair_obj);
+
+/// Returns the ValueObjectSP of the child of \c obj. If \c obj has no
+/// child named \c child_name, returns the __compressed_pair child instead
+/// with \c compressed_pair_name, if one exists.
+///
+/// Latest libc++ wrap the compressed children in an anonymous structure.
+/// The \c anon_struct_idx indicates the location of this struct.
+///
+/// The returned boolean is \c true if the returned child was has an old-style
+/// libc++ __compressed_pair layout.
+///
+/// If no child was found returns a nullptr.
+std::pair<lldb::ValueObjectSP, bool>
+GetValueOrOldCompressedPair(ValueObject &obj, size_t anon_struct_idx,
+                            llvm::StringRef child_name,
+                            llvm::StringRef compressed_pair_name);
 bool isStdTemplate(ConstString type_name, llvm::StringRef type);
 
 bool LibcxxStringSummaryProviderASCII(

lldb/source/Plugins/Language/CPlusPlus/LibCxxMap.cpp

@@ -200,7 +200,8 @@ class LibcxxStdMapSyntheticFrontEnd : public SyntheticChildrenFrontEnd {
   llvm::Expected<size_t> GetIndexOfChildWithName(ConstString name) override;
 
 private:
-  llvm::Expected<uint32_t> CalculateNumChildrenForOldCompressedPairLayout();
+  llvm::Expected<uint32_t>
+  CalculateNumChildrenForOldCompressedPairLayout(ValueObject &pair);
 
   /// Returns the ValueObject for the __tree_node type that
   /// holds the key/value pair of the node at index \ref idx.
@@ -254,16 +255,8 @@ lldb_private::formatters::LibcxxStdMapSyntheticFrontEnd::
 
 llvm::Expected<uint32_t>
 lldb_private::formatters::LibcxxStdMapSyntheticFrontEnd::
-    CalculateNumChildrenForOldCompressedPairLayout() {
-  ValueObjectSP node_sp(m_tree->GetChildMemberWithName("__pair3_"));
-  if (!node_sp)
-    return 0;
-
-  if (!isOldCompressedPairLayout(*node_sp))
-    return llvm::createStringError("Unexpected std::map layout: expected "
-                                   "old __compressed_pair layout.");
-
-  node_sp = GetFirstValueOfLibCXXCompressedPair(*node_sp);
+    CalculateNumChildrenForOldCompressedPairLayout(ValueObject &pair) {
+  auto node_sp = GetFirstValueOfLibCXXCompressedPair(pair);
 
   if (!node_sp)
     return 0;
@@ -281,12 +274,16 @@ llvm::Expected<uint32_t> lldb_private::formatters::
   if (m_tree == nullptr)
     return 0;
 
-  if (auto node_sp = m_tree->GetChildMemberWithName("__size_")) {
-    m_count = node_sp->GetValueAsUnsigned(0);
-    return m_count;
-  }
+  auto [size_sp, is_compressed_pair] = GetValueOrOldCompressedPair(
+      *m_tree, /*anon_struct_idx=*/2, "__size_", "__pair3_");
+  if (!size_sp)
+    return llvm::createStringError("Unexpected std::map layout");
 
-  return CalculateNumChildrenForOldCompressedPairLayout();
+  if (is_compressed_pair)
+    return CalculateNumChildrenForOldCompressedPairLayout(*size_sp);
+
+  m_count = size_sp->GetValueAsUnsigned(0);
+  return m_count;
 }
 
 ValueObjectSP

lldb/source/Plugins/Language/CPlusPlus/LibCxxUnorderedMap.cpp

@@ -130,22 +130,17 @@ CompilerType lldb_private::formatters::LibcxxStdUnorderedMapSyntheticFrontEnd::
 
 CompilerType lldb_private::formatters::LibcxxStdUnorderedMapSyntheticFrontEnd::
     GetNodeType() {
-  auto node_sp = m_backend.GetChildAtNamePath({"__table_", "__first_node_"});
-
-  if (!node_sp) {
-    auto p1_sp = m_backend.GetChildAtNamePath({"__table_", "__p1_"});
-    if (!p1_sp)
-      return {};
+  auto table_sp = m_backend.GetChildMemberWithName("__table_");
+  if (!table_sp)
+    return {};
 
-    if (!isOldCompressedPairLayout(*p1_sp))
-      return {};
+  auto [node_sp, is_compressed_pair] = GetValueOrOldCompressedPair(
+      *table_sp, /*anon_struct_idx=*/1, "__first_node_", "__p1_");
+  if (is_compressed_pair)
+    node_sp = GetFirstValueOfLibCXXCompressedPair(*node_sp);
 
-    node_sp = GetFirstValueOfLibCXXCompressedPair(*p1_sp);
-    if (!node_sp)
-      return {};
-  }
-
-  assert(node_sp);
+  if (!node_sp)
+    return {};
 
   return node_sp->GetCompilerType().GetTypeTemplateArgument(0).GetPointeeType();
 }
@@ -223,19 +218,15 @@ lldb::ValueObjectSP lldb_private::formatters::
 llvm::Expected<size_t>
 lldb_private::formatters::LibcxxStdUnorderedMapSyntheticFrontEnd::
     CalculateNumChildrenImpl(ValueObject &table) {
-  if (auto size_sp = table.GetChildMemberWithName("__size_"))
+  auto [size_sp, is_compressed_pair] = GetValueOrOldCompressedPair(
+      table, /*anon_struct_idx=*/2, "__size_", "__p2_");
+  if (!is_compressed_pair && size_sp)
     return size_sp->GetValueAsUnsigned(0);
 
-  ValueObjectSP p2_sp = table.GetChildMemberWithName("__p2_");
-  if (!p2_sp)
-    return llvm::createStringError(
-        "Unexpected std::unordered_map layout: __p2_ member not found.");
+  if (!is_compressed_pair)
+    return llvm::createStringError("Unsupported std::unordered_map layout.");
 
-  if (!isOldCompressedPairLayout(*p2_sp))
-    return llvm::createStringError("Unexpected std::unordered_map layout: old "
-                                   "__compressed_pair layout not found.");
-
-  ValueObjectSP num_elements_sp = GetFirstValueOfLibCXXCompressedPair(*p2_sp);
+  ValueObjectSP num_elements_sp = GetFirstValueOfLibCXXCompressedPair(*size_sp);
 
   if (!num_elements_sp)
     return llvm::createStringError(
@@ -246,19 +237,13 @@ lldb_private::formatters::LibcxxStdUnorderedMapSyntheticFrontEnd::
 }
 
 static ValueObjectSP GetTreePointer(ValueObject &table) {
-  ValueObjectSP tree_sp = table.GetChildMemberWithName("__first_node_");
-  if (!tree_sp) {
-    ValueObjectSP p1_sp = table.GetChildMemberWithName("__p1_");
-    if (!p1_sp)
-      return nullptr;
-
-    if (!isOldCompressedPairLayout(*p1_sp))
-      return nullptr;
-
-    tree_sp = GetFirstValueOfLibCXXCompressedPair(*p1_sp);
-    if (!tree_sp)
-      return nullptr;
-  }
+  auto [tree_sp, is_compressed_pair] = GetValueOrOldCompressedPair(
+      table, /*anon_struct_idx=*/1, "__first_node_", "__p1_");
+  if (is_compressed_pair)
+    tree_sp = GetFirstValueOfLibCXXCompressedPair(*tree_sp);
+
+  if (!tree_sp)
+    return nullptr;
 
   return tree_sp->GetChildMemberWithName("__next_");
 }

lldb/source/Plugins/Language/CPlusPlus/LibCxxVector.cpp

@@ -126,17 +126,15 @@ lldb_private::formatters::LibcxxStdVectorSyntheticFrontEnd::GetChildAtIndex(
 }
 
 static ValueObjectSP GetDataPointer(ValueObject &root) {
-  if (auto cap_sp = root.GetChildMemberWithName("__cap_"))
-    return cap_sp;
-
-  ValueObjectSP cap_sp = root.GetChildMemberWithName("__end_cap_");
+  auto [cap_sp, is_compressed_pair] = GetValueOrOldCompressedPair(
+      root, /*anon_struct_idx=*/2, "__cap_", "__end_cap_");
   if (!cap_sp)
     return nullptr;
 
-  if (!isOldCompressedPairLayout(*cap_sp))
-    return nullptr;
+  if (is_compressed_pair)
+    return GetFirstValueOfLibCXXCompressedPair(*cap_sp);
 
-  return GetFirstValueOfLibCXXCompressedPair(*cap_sp);
+  return cap_sp;
 }
 
 lldb::ChildCacheState

lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx-simulators/invalid-vector/main.cpp

@@ -1,4 +1,4 @@
-#define COMPRESSED_PAIR_REV 3
+#define COMPRESSED_PAIR_REV 4
 #include <libcxx-simulators-common/compressed_pair.h>
 
 namespace std {