[libcxx-commits] [libcxx] [libc++] Remove potential 0-sized array in __compressed_pair_padding (PR #109028)

[via libcxx-commits]

https://github.com/serge-sans-paille updated https://github.com/llvm/llvm-project/pull/109028

>From 06e7122cca9468db17b0415aa37f9124783164e0 Mon Sep 17 00:00:00 2001
From: serge-sans-paille <sguelton at mozilla.com>
Date: Tue, 17 Sep 2024 20:39:05 +0200
Subject: [PATCH 1/3] [libc++] Remove potential 0-sized array in
 __compressed_pair_padding

---
 libcxx/include/__memory/compressed_pair.h | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/libcxx/include/__memory/compressed_pair.h b/libcxx/include/__memory/compressed_pair.h
index 629e3ad8848ffa..77928af434f1f4 100644
--- a/libcxx/include/__memory/compressed_pair.h
+++ b/libcxx/include/__memory/compressed_pair.h
@@ -52,13 +52,16 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 
 #ifndef _LIBCPP_ABI_NO_COMPRESSED_PAIR_PADDING
 
-template <class _ToPad>
+template <class _ToPad,
+          bool _Empty = ((is_empty<_ToPad>::value && !__libcpp_is_final<_ToPad>::value) ||
+                         is_reference<_ToPad>::value || sizeof(_ToPad) - __datasizeof_v<_ToPad> == 0)>
 class __compressed_pair_padding {
-  char __padding_[((is_empty<_ToPad>::value && !__libcpp_is_final<_ToPad>::value) || is_reference<_ToPad>::value)
-                      ? 0
-                      : sizeof(_ToPad) - __datasizeof_v<_ToPad>];
+  char __padding_[sizeof(_ToPad) - __datasizeof_v<_ToPad>];
 };
 
+template <class _ToPad>
+class __compressed_pair_padding<_ToPad, true> {};
+
 #  define _LIBCPP_COMPRESSED_PAIR(T1, Initializer1, T2, Initializer2)                                                  \
     _LIBCPP_NO_UNIQUE_ADDRESS __attribute__((__aligned__(_LIBCPP_ALIGNOF(T2)))) T1 Initializer1;                       \
     _LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T1> _LIBCPP_CONCAT3(__padding1_, __LINE__, _);          \

>From dae40cdb2b64e7253f854314b46bb0c876129a66 Mon Sep 17 00:00:00 2001
From: serge-sans-paille <sguelton at mozilla.com>
Date: Wed, 18 Sep 2024 11:25:18 +0200
Subject: [PATCH 2/3] [libc++] Remove potential 0-sized array in
 __packed_format_arg_store

---
 libcxx/include/__format/format_arg_store.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/libcxx/include/__format/format_arg_store.h b/libcxx/include/__format/format_arg_store.h
index 68e936acecade7..9a4a41df6d4e68 100644
--- a/libcxx/include/__format/format_arg_store.h
+++ b/libcxx/include/__format/format_arg_store.h
@@ -234,6 +234,11 @@ struct __packed_format_arg_store {
   uint64_t __types_ = 0;
 };
 
+template <class _Context>
+struct __packed_format_arg_store<_Context, 0> {
+  uint64_t __types_ = 0;
+};
+
 template <class _Context, size_t _Np>
 struct __unpacked_format_arg_store {
   basic_format_arg<_Context> __args_[_Np];

>From 3d28f771e26fa332a1121c67408ae621bb620f19 Mon Sep 17 00:00:00 2001
From: serge-sans-paille <sguelton at mozilla.com>
Date: Wed, 18 Sep 2024 16:51:50 +0200
Subject: [PATCH 3/3] fixup! [libc++] Remove potential 0-sized array in
 __compressed_pair_padding

---
 libcxx/include/__memory/compressed_pair.h | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/libcxx/include/__memory/compressed_pair.h b/libcxx/include/__memory/compressed_pair.h
index 77928af434f1f4..d955aebad63e31 100644
--- a/libcxx/include/__memory/compressed_pair.h
+++ b/libcxx/include/__memory/compressed_pair.h
@@ -52,15 +52,11 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 
 #ifndef _LIBCPP_ABI_NO_COMPRESSED_PAIR_PADDING
 
-template <class _ToPad,
-          bool _Empty = ((is_empty<_ToPad>::value && !__libcpp_is_final<_ToPad>::value) ||
-                         is_reference<_ToPad>::value || sizeof(_ToPad) - __datasizeof_v<_ToPad> == 0)>
-class __compressed_pair_padding {
-  char __padding_[sizeof(_ToPad) - __datasizeof_v<_ToPad>];
-};
-
 template <class _ToPad>
-class __compressed_pair_padding<_ToPad, true> {};
+using __compressed_pair_padding =
+    __padding<((is_empty<_ToPad>::value && !__libcpp_is_final<_ToPad>::value) || is_reference<_ToPad>::value)
+                  ? 0
+                  : (sizeof(_ToPad) - __datasizeof_v<_ToPad>)>;
 
 #  define _LIBCPP_COMPRESSED_PAIR(T1, Initializer1, T2, Initializer2)                                                  \
     _LIBCPP_NO_UNIQUE_ADDRESS __attribute__((__aligned__(_LIBCPP_ALIGNOF(T2)))) T1 Initializer1;                       \