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🍒[lldb][DataFormatters] Support newer _LIBCPP_COMPRESSED_PAIR layout #11258

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🍒[lldb][DataFormatters] Support newer _LIBCPP_COMPRESSED_PAIR layout #11258

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04975df
[lldb][test] Synchronize `__compressed_pair_padding` with libc++ (#14…
frederick-vs-ja Jul 3, 2025
b3a9d00
[lldb][test][NFC] Re-arrange ifdefs in compressed_pair.h
Michael137 Aug 24, 2025
eb0c070
[lldb][DataFormatters] Support newer _LIBCPP_COMPRESSED_PAIR layout (…
Michael137 Aug 25, 2025
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101 changes: 76 additions & 25 deletions lldb/packages/Python/lldbsuite/test/make/libcxx-simulators-common/compressed_pair.h
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,14 @@
#include <type_traits>
#include <utility> // for std::forward

// COMPRESSED_PAIR_REV versions:
// 0 -> Post-c88580c layout
// 1 -> Post-27c83382d83dc layout
// 2 -> Post-769c42f4a552a layout
// 3 -> Post-f5e687d7bf49c layout
// 4 -> padding-less no_unique_address-based layout (introduced in
// 27c83382d83dc)

namespace std {
namespace __lldb {

Expand All @@ -13,7 +21,50 @@ namespace __lldb {
#define _LLDB_NO_UNIQUE_ADDRESS [[__no_unique_address__]]
#endif

#if COMPRESSED_PAIR_REV == 0 // Post-c88580c layout
// From libc++ datasizeof.h
template <class _Tp> struct _FirstPaddingByte {
_LLDB_NO_UNIQUE_ADDRESS _Tp __v_;
char __first_padding_byte_;
};

template <class _Tp>
inline const size_t __datasizeof_v =
__builtin_offsetof(_FirstPaddingByte<_Tp>, __first_padding_byte_);

template <class _Tp>
struct __lldb_is_final : public integral_constant<bool, __is_final(_Tp)> {};

// The legacy layout has been patched, see
// https://github.com/llvm/llvm-project/pull/142516.
#if COMPRESSED_PAIR_REV == 1
template <class _ToPad> class __compressed_pair_padding {
char __padding_[((is_empty<_ToPad>::value &&
!__lldb_is_final<_ToPad>::value) ||
is_reference<_ToPad>::value)
? 0
: sizeof(_ToPad) - __datasizeof_v<_ToPad>];
};
#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) ||
sizeof(_ToPad) == __datasizeof_v<_ToPad>;

template <class _Tp>
inline const bool __is_reference_or_unpadded_object<_Tp &> = true;

template <class _Tp>
inline const bool __is_reference_or_unpadded_object<_Tp &&> = true;

template <class _ToPad, bool _Empty = __is_reference_or_unpadded_object<_ToPad>>
class __compressed_pair_padding {
char __padding_[sizeof(_ToPad) - __datasizeof_v<_ToPad>] = {};
};

template <class _ToPad> class __compressed_pair_padding<_ToPad, true> {};
#endif // COMPRESSED_PAIR_REV == 1

#if COMPRESSED_PAIR_REV == 0
struct __value_init_tag {};
struct __default_init_tag {};

Expand Down Expand Up @@ -58,28 +109,7 @@ class __compressed_pair : private __compressed_pair_elem<_T1, 0>,

_T1 &first() { return static_cast<_Base1 &>(*this).__get(); }
};
#elif COMPRESSED_PAIR_REV == 1
// From libc++ datasizeof.h
template <class _Tp> struct _FirstPaddingByte {
_LLDB_NO_UNIQUE_ADDRESS _Tp __v_;
char __first_padding_byte_;
};

template <class _Tp>
inline const size_t __datasizeof_v =
__builtin_offsetof(_FirstPaddingByte<_Tp>, __first_padding_byte_);

template <class _Tp>
struct __lldb_is_final : public integral_constant<bool, __is_final(_Tp)> {};

template <class _ToPad> class __compressed_pair_padding {
char __padding_[((is_empty<_ToPad>::value &&
!__lldb_is_final<_ToPad>::value) ||
is_reference<_ToPad>::value)
? 0
: sizeof(_ToPad) - __datasizeof_v<_ToPad>];
};

#elif COMPRESSED_PAIR_REV == 1 || COMPRESSED_PAIR_REV == 2
#define _LLDB_COMPRESSED_PAIR(T1, Initializer1, T2, Initializer2) \
[[__gnu__::__aligned__( \
alignof(T2))]] _LLDB_NO_UNIQUE_ADDRESS T1 Initializer1; \
Expand All @@ -96,7 +126,28 @@ template <class _ToPad> class __compressed_pair_padding {
_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 == 2
#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
Expand All @@ -105,7 +156,7 @@ template <class _ToPad> class __compressed_pair_padding {
_LLDB_NO_UNIQUE_ADDRESS T1 Name1; \
_LLDB_NO_UNIQUE_ADDRESS T2 Name2; \
_LLDB_NO_UNIQUE_ADDRESS T3 Name3
#endif
#endif // COMPRESSED_PAIR_REV == 3
} // namespace __lldb
} // namespace std

Expand Down
67 changes: 50 additions & 17 deletions lldb/source/Plugins/Language/CPlusPlus/LibCxx.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -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();
Expand Down Expand Up @@ -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) {

Expand Down Expand Up @@ -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)
Expand Down Expand Up @@ -382,13 +416,14 @@ 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"));
Expand Down Expand Up @@ -442,17 +477,15 @@ 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
Expand Down
17 changes: 16 additions & 1 deletion lldb/source/Plugins/Language/CPlusPlus/LibCxx.h
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Original file line number Diff line number Diff line change
Expand Up @@ -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(
Expand Down
24 changes: 12 additions & 12 deletions lldb/source/Plugins/Language/CPlusPlus/LibCxxList.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -293,11 +293,18 @@ lldb::ChildCacheState ForwardListFrontEnd::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)
Expand All @@ -320,17 +327,10 @@ llvm::Expected<uint32_t> ListFrontEnd::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);
Expand Down
29 changes: 13 additions & 16 deletions lldb/source/Plugins/Language/CPlusPlus/LibCxxMap.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -202,7 +202,8 @@ class LibcxxStdMapSyntheticFrontEnd : public SyntheticChildrenFrontEnd {
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.
Expand Down Expand Up @@ -258,16 +259,8 @@ 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;
Expand All @@ -285,12 +278,16 @@ 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
Expand Down
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