[lldb][test] Synchronize __compressed_pair_padding with libc++

[frederick-vs-ja]

This PR mirrors changes of __compressed_pair_padding in libc++ into lldb test suite.

Related PR for libc++:

• [libc++] Fix constant initialization of unique_ptr in C++17 and prior #108956
• [libc++] Remove potential 0-sized array in __compressed_pair_padding #109028
• [libc++] Fix padding calculation for function reference types #142125

[llvmbot]

@llvm/pr-subscribers-lldb

Author: A. Jiang (frederick-vs-ja)

Changes

This PR mirrors changes of __compressed_pair_padding in libc++ into lldb test suite.

Related PR for libc++:

• #108956
• #109028
• #142125

---

Full diff: https://github.com/llvm/llvm-project/pull/142516.diff

1 Files Affected:

• (modified) lldb/packages/Python/lldbsuite/test/make/libcxx-simulators-common/compressed_pair.h (+16-6)

diff --git a/lldb/packages/Python/lldbsuite/test/make/libcxx-simulators-common/compressed_pair.h b/lldb/packages/Python/lldbsuite/test/make/libcxx-simulators-common/compressed_pair.h
index 6dc53a4e88ffd..3f305bdcb4d54 100644
--- a/lldb/packages/Python/lldbsuite/test/make/libcxx-simulators-common/compressed_pair.h
+++ b/lldb/packages/Python/lldbsuite/test/make/libcxx-simulators-common/compressed_pair.h
@@ -72,14 +72,24 @@ inline const size_t __datasizeof_v =
 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>];
+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> {};
+
 #define _LLDB_COMPRESSED_PAIR(T1, Initializer1, T2, Initializer2)              \
   [[__gnu__::__aligned__(                                                      \
       alignof(T2))]] _LLDB_NO_UNIQUE_ADDRESS T1 Initializer1;                  \

[Michael137]

Thanks for keeping this in sync! What we would usually do with these simulators is to add the new implementation behind a ifdef COMPRESSED_PAIR_REV == <new version>. To make sure we don't regress users still on the older layout. Do you mind doing that? If it's too finicky I'm happy to give it a shot

[frederick-vs-ja]

Sorry for late replying. I'll do this soon I've done this, although this seems unnecessary as there doesn't seem any case where the layout will change.

[Michael137]

Thanks for adjusting! I know it's quite gnarly with all these ifdefs