[lldb][DataFormatters] Support newer _LIBCPP_COMPRESSED_PAIR layout

[Michael137]

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.

[llvmbot]

@llvm/pr-subscribers-lldb

Author: Michael Buch (Michael137)

Changes

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

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

---

Full diff: https://github.com/llvm/llvm-project/pull/155153.diff

6 Files Affected:

• (modified) lldb/source/Plugins/Language/CPlusPlus/GenericList.cpp (+12-12)
• (modified) lldb/source/Plugins/Language/CPlusPlus/LibCxx.cpp (+35-2)
• (modified) lldb/source/Plugins/Language/CPlusPlus/LibCxx.h (+16-1)
• (modified) lldb/source/Plugins/Language/CPlusPlus/LibCxxMap.cpp (+13-16)
• (modified) lldb/source/Plugins/Language/CPlusPlus/LibCxxUnorderedMap.cpp (+22-37)
• (modified) lldb/source/Plugins/Language/CPlusPlus/LibCxxVector.cpp (+5-7)

diff --git a/lldb/source/Plugins/Language/CPlusPlus/GenericList.cpp b/lldb/source/Plugins/Language/CPlusPlus/GenericList.cpp
index ea1edbfd3ac9b..5289027fbd8af 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/GenericList.cpp
+++ b/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);
diff --git a/lldb/source/Plugins/Language/CPlusPlus/LibCxx.cpp b/lldb/source/Plugins/Language/CPlusPlus/LibCxx.cpp
index a7874047942c4..6d41132122641 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/LibCxx.cpp
+++ b/lldb/source/Plugins/Language/CPlusPlus/LibCxx.cpp
@@ -49,8 +49,7 @@ static void consumeInlineNamespace(llvm::StringRef &name) {
   }
 }
 
-bool lldb_private::formatters::isOldCompressedPairLayout(
-    ValueObject &pair_obj) {
+static bool isOldCompressedPairLayout(ValueObject &pair_obj) {
   return isStdTemplate(pair_obj.GetTypeName(), "__compressed_pair");
 }
 
@@ -105,6 +104,40 @@ 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) {
+  // 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, isOldCompressedPairLayout(*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, isOldCompressedPairLayout(*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 (!isOldCompressedPairLayout(*node_sp))
+    return {nullptr, false};
+
+  return {node_sp, true};
+}
+
 bool lldb_private::formatters::LibcxxFunctionSummaryProvider(
     ValueObject &valobj, Stream &stream, const TypeSummaryOptions &options) {
 
diff --git a/lldb/source/Plugins/Language/CPlusPlus/LibCxx.h b/lldb/source/Plugins/Language/CPlusPlus/LibCxx.h
index d88a6ecb1fa89..819f8a985f9b9 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/LibCxx.h
+++ b/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(
diff --git a/lldb/source/Plugins/Language/CPlusPlus/LibCxxMap.cpp b/lldb/source/Plugins/Language/CPlusPlus/LibCxxMap.cpp
index 41441dfbc7180..85766966f1554 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/LibCxxMap.cpp
+++ b/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
diff --git a/lldb/source/Plugins/Language/CPlusPlus/LibCxxUnorderedMap.cpp b/lldb/source/Plugins/Language/CPlusPlus/LibCxxUnorderedMap.cpp
index 501fd0945b82c..f88a5319068a2 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/LibCxxUnorderedMap.cpp
+++ b/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_");
 }
diff --git a/lldb/source/Plugins/Language/CPlusPlus/LibCxxVector.cpp b/lldb/source/Plugins/Language/CPlusPlus/LibCxxVector.cpp
index 4bcdf01c221a3..60913e5c1ac56 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/LibCxxVector.cpp
+++ b/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

[nikic]

/cherry-pick 7b22660 20dd053

[llvmbot]

/pull-request #155366