[libc++] Refactor vector's ASan annotations to only ever delete and add the annotations

[philnik777]

This significantly simplifies the places where we insert/delete elements, since the code is exactly what you'd naively implement now. This also probably fixes some annotation issues when exceptions are thrown, since that will be handled correctly now through __scope_guard.

[github-actions]

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diff --git a/libcxx/include/__utility/scope_guard.h b/libcxx/include/__utility/scope_guard.h
index 24f96e5b5..e833c95f5 100644
--- a/libcxx/include/__utility/scope_guard.h
+++ b/libcxx/include/__utility/scope_guard.h
@@ -37,10 +37,10 @@ public:
 // C++14 doesn't have mandatory RVO, so we have to provide a declaration even though no compiler will ever generate
 // a call to the move constructor.
 #if _LIBCPP_STD_VER <= 14
-_LIBCPP_DIAGNOSTIC_PUSH
-_LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wundefined-internal")
+  _LIBCPP_DIAGNOSTIC_PUSH
+  _LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wundefined-internal")
   __scope_guard(__scope_guard&&);
-_LIBCPP_DIAGNOSTIC_POP
+  _LIBCPP_DIAGNOSTIC_POP
 #else
   __scope_guard(__scope_guard&&) = delete;
 #endif

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: Nikolas Klauser (philnik777)

Changes

This significantly simplifies the places where we insert/delete elements, since the code is exactly what you'd naively implement now. This also probably fixes some annotation issues when exceptions are thrown, since that will be handled correctly now through __scope_guard.

---

Full diff: https://github.com/llvm/llvm-project/pull/152967.diff

2 Files Affected:

• (modified) libcxx/include/__utility/scope_guard.h (+3)
• (modified) libcxx/include/__vector/vector.h (+43-60)

diff --git a/libcxx/include/__utility/scope_guard.h b/libcxx/include/__utility/scope_guard.h
index 3972102eee891..24f96e5b5fb53 100644
--- a/libcxx/include/__utility/scope_guard.h
+++ b/libcxx/include/__utility/scope_guard.h
@@ -37,7 +37,10 @@ class __scope_guard {
 // C++14 doesn't have mandatory RVO, so we have to provide a declaration even though no compiler will ever generate
 // a call to the move constructor.
 #if _LIBCPP_STD_VER <= 14
+_LIBCPP_DIAGNOSTIC_PUSH
+_LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wundefined-internal")
   __scope_guard(__scope_guard&&);
+_LIBCPP_DIAGNOSTIC_POP
 #else
   __scope_guard(__scope_guard&&) = delete;
 #endif
diff --git a/libcxx/include/__vector/vector.h b/libcxx/include/__vector/vector.h
index 4307e78f6ddbc..c4d56a49f218f 100644
--- a/libcxx/include/__vector/vector.h
+++ b/libcxx/include/__vector/vector.h
@@ -65,6 +65,7 @@
 #include <__utility/is_pointer_in_range.h>
 #include <__utility/move.h>
 #include <__utility/pair.h>
+#include <__utility/scope_guard.h>
 #include <__utility/swap.h>
 #include <initializer_list>
 #include <limits>
@@ -479,9 +480,10 @@ class vector {
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __emplace_back_assume_capacity(_Args&&... __args) {
     _LIBCPP_ASSERT_INTERNAL(
         size() < capacity(), "We assume that we have enough space to insert an element at the end of the vector");
-    _ConstructTransaction __tx(*this, 1);
-    __alloc_traits::construct(this->__alloc_, std::__to_address(__tx.__pos_), std::forward<_Args>(__args)...);
-    ++__tx.__pos_;
+    __annotate_delete();
+    auto __guard = std::__make_scope_guard(__annotate_new_size(*this));
+    __alloc_traits::construct(this->__alloc_, std::__to_address(__end_), std::forward<_Args>(__args)...);
+    ++__end_;
   }
 
 #if _LIBCPP_STD_VER >= 23
@@ -548,9 +550,9 @@ class vector {
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI iterator erase(const_iterator __first, const_iterator __last);
 
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void clear() _NOEXCEPT {
-    size_type __old_size = size();
+    __annotate_delete();
+    auto __guard = std::__make_scope_guard(__annotate_new_size(*this));
     __base_destruct_at_end(this->__begin_);
-    __annotate_shrink(__old_size);
   }
 
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void resize(size_type __sz);
@@ -599,7 +601,7 @@ class vector {
 
     if (__n > 0) {
       __vallocate(__n);
-      __construct_at_end(std::move(__first), std::move(__last), __n);
+      __construct_at_end(std::move(__first), std::move(__last));
     }
 
     __guard.__complete();
@@ -659,8 +661,7 @@ class vector {
   __insert_with_size(const_iterator __position, _Iterator __first, _Sentinel __last, difference_type __n);
 
   template <class _InputIterator, class _Sentinel>
-  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void
-  __construct_at_end(_InputIterator __first, _Sentinel __last, size_type __n);
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __construct_at_end(_InputIterator __first, _Sentinel __last);
 
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __append(size_type __n);
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __append(size_type __n, const_reference __x);
@@ -708,9 +709,9 @@ class vector {
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __move_assign(vector& __c, false_type)
       _NOEXCEPT_(__alloc_traits::is_always_equal::value);
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __destruct_at_end(pointer __new_last) _NOEXCEPT {
-    size_type __old_size = size();
+    __annotate_delete();
+    auto __guard = std::__make_scope_guard(__annotate_new_size(*this));
     __base_destruct_at_end(__new_last);
-    __annotate_shrink(__old_size);
   }
 
   template <class... _Args>
@@ -737,33 +738,11 @@ class vector {
     __annotate_contiguous_container(data() + size(), data() + capacity());
   }
 
-  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __annotate_increase(size_type __n) const _NOEXCEPT {
-    __annotate_contiguous_container(data() + size(), data() + size() + __n);
-  }
-
-  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __annotate_shrink(size_type __old_size) const _NOEXCEPT {
-    __annotate_contiguous_container(data() + __old_size, data() + size());
-  }
-
-  struct _ConstructTransaction {
-    _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI explicit _ConstructTransaction(vector& __v, size_type __n)
-        : __v_(__v), __pos_(__v.__end_), __new_end_(__v.__end_ + __n) {
-      __v_.__annotate_increase(__n);
-    }
-
-    _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI ~_ConstructTransaction() {
-      __v_.__end_ = __pos_;
-      if (__pos_ != __new_end_) {
-        __v_.__annotate_shrink(__new_end_ - __v_.__begin_);
-      }
-    }
-
-    vector& __v_;
-    pointer __pos_;
-    const_pointer const __new_end_;
+  struct __annotate_new_size {
+    vector& __vec_;
 
-    _ConstructTransaction(_ConstructTransaction const&)            = delete;
-    _ConstructTransaction& operator=(_ConstructTransaction const&) = delete;
+    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __annotate_new_size(vector& __vec) : __vec_(__vec) {}
+    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void operator()() { __vec_.__annotate_new(__vec_.size()); }
   };
 
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __base_destruct_at_end(pointer __new_last) _NOEXCEPT {
@@ -850,6 +829,7 @@ template <class _Tp, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20 void
 vector<_Tp, _Allocator>::__swap_out_circular_buffer(__split_buffer<value_type, allocator_type&>& __v) {
   __annotate_delete();
+  auto __guard = std::__make_scope_guard(__annotate_new_size(*this));
   auto __new_begin = __v.__begin_ - (__end_ - __begin_);
   std::__uninitialized_allocator_relocate(
       this->__alloc_, std::__to_address(__begin_), std::__to_address(__end_), std::__to_address(__new_begin));
@@ -859,7 +839,6 @@ vector<_Tp, _Allocator>::__swap_out_circular_buffer(__split_buffer<value_type, a
   std::swap(this->__end_, __v.__end_);
   std::swap(this->__cap_, __v.__cap_);
   __v.__first_ = __v.__begin_;
-  __annotate_new(size());
 }
 
 // __swap_out_circular_buffer relocates the objects in [__begin_, __p) into the front of __v, the objects in
@@ -870,6 +849,7 @@ template <class _Tp, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20 typename vector<_Tp, _Allocator>::pointer
 vector<_Tp, _Allocator>::__swap_out_circular_buffer(__split_buffer<value_type, allocator_type&>& __v, pointer __p) {
   __annotate_delete();
+  auto __guard = std::__make_scope_guard(__annotate_new_size(*this));
   pointer __ret = __v.__begin_;
 
   // Relocate [__p, __end_) first to avoid having a hole in [__begin_, __end_)
@@ -889,7 +869,6 @@ vector<_Tp, _Allocator>::__swap_out_circular_buffer(__split_buffer<value_type, a
   std::swap(this->__end_, __v.__end_);
   std::swap(this->__cap_, __v.__cap_);
   __v.__first_ = __v.__begin_;
-  __annotate_new(size());
   return __ret;
 }
 
@@ -923,10 +902,12 @@ vector<_Tp, _Allocator>::__recommend(size_type __new_size) const {
 //  Postcondition:  size() == size() + __n
 template <class _Tp, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20 void vector<_Tp, _Allocator>::__construct_at_end(size_type __n) {
-  _ConstructTransaction __tx(*this, __n);
-  const_pointer __new_end = __tx.__new_end_;
-  for (pointer __pos = __tx.__pos_; __pos != __new_end; __tx.__pos_ = ++__pos) {
-    __alloc_traits::construct(this->__alloc_, std::__to_address(__pos));
+  __annotate_delete();
+  auto __guard = std::__make_scope_guard(__annotate_new_size(*this));
+
+  for (size_t __i = 0; __i != __n; ++__i) {
+    __alloc_traits::construct(this->__alloc_, std::__to_address(__end_));
+    ++__end_;
   }
 }
 
@@ -939,19 +920,21 @@ _LIBCPP_CONSTEXPR_SINCE_CXX20 void vector<_Tp, _Allocator>::__construct_at_end(s
 template <class _Tp, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20 inline void
 vector<_Tp, _Allocator>::__construct_at_end(size_type __n, const_reference __x) {
-  _ConstructTransaction __tx(*this, __n);
-  const_pointer __new_end = __tx.__new_end_;
-  for (pointer __pos = __tx.__pos_; __pos != __new_end; __tx.__pos_ = ++__pos) {
-    __alloc_traits::construct(this->__alloc_, std::__to_address(__pos), __x);
+  __annotate_delete();
+  auto __guard = std::__make_scope_guard(__annotate_new_size(*this));
+
+  for (size_t __i = 0; __i != __n; ++__i) {
+    __alloc_traits::construct(this->__alloc_, std::__to_address(__end_), __x);
+    ++__end_;
   }
 }
 
 template <class _Tp, class _Allocator>
 template <class _InputIterator, class _Sentinel>
 _LIBCPP_CONSTEXPR_SINCE_CXX20 void
-vector<_Tp, _Allocator>::__construct_at_end(_InputIterator __first, _Sentinel __last, size_type __n) {
-  _ConstructTransaction __tx(*this, __n);
-  __tx.__pos_ = std::__uninitialized_allocator_copy(this->__alloc_, std::move(__first), std::move(__last), __tx.__pos_);
+vector<_Tp, _Allocator>::__construct_at_end(_InputIterator __first, _Sentinel __last) {
+  auto __guard = std::__make_scope_guard(__annotate_new_size(*this));
+  __end_       = std::__uninitialized_allocator_copy(this->__alloc_, std::move(__first), std::move(__last), __end_);
 }
 
 //  Default constructs __n objects starting at __end_
@@ -1068,12 +1051,11 @@ vector<_Tp, _Allocator>::__assign_with_size(_Iterator __first, _Sentinel __last,
     if (__new_size > size()) {
 #if _LIBCPP_STD_VER >= 23
       auto __mid = ranges::copy_n(std::move(__first), size(), this->__begin_).in;
-      __construct_at_end(std::move(__mid), std::move(__last), __new_size - size());
 #else
       _Iterator __mid = std::next(__first, size());
       std::copy(__first, __mid, this->__begin_);
-      __construct_at_end(__mid, __last, __new_size - size());
 #endif
+      __construct_at_end(std::move(__mid), std::move(__last));
     } else {
       pointer __m = std::__copy(std::move(__first), __last, this->__begin_).second;
       this->__destruct_at_end(__m);
@@ -1081,7 +1063,7 @@ vector<_Tp, _Allocator>::__assign_with_size(_Iterator __first, _Sentinel __last,
   } else {
     __vdeallocate();
     __vallocate(__recommend(__new_size));
-    __construct_at_end(std::move(__first), std::move(__last), __new_size);
+    __construct_at_end(std::move(__first), std::move(__last));
   }
 }
 
@@ -1189,15 +1171,16 @@ vector<_Tp, _Allocator>::erase(const_iterator __first, const_iterator __last) {
 template <class _Tp, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20 void
 vector<_Tp, _Allocator>::__move_range(pointer __from_s, pointer __from_e, pointer __to) {
+  __annotate_delete();
+  auto __guard = std::__make_scope_guard(__annotate_new_size(*this));
   pointer __old_last  = this->__end_;
   difference_type __n = __old_last - __to;
-  {
-    pointer __i = __from_s + __n;
-    _ConstructTransaction __tx(*this, __from_e - __i);
-    for (pointer __pos = __tx.__pos_; __i < __from_e; ++__i, (void)++__pos, __tx.__pos_ = __pos) {
-      __alloc_traits::construct(this->__alloc_, std::__to_address(__pos), std::move(*__i));
-    }
+
+  for (pointer __i = __from_s + __n; __i != __from_e; ++__i) {
+    __alloc_traits::construct(this->__alloc_, std::__to_address(__end_), std::move(*__i));
+    ++__end_;
   }
+
   std::move_backward(__from_s, __from_s + __n, __old_last);
 }
 
@@ -1338,13 +1321,13 @@ vector<_Tp, _Allocator>::__insert_with_size(
       if (__n > __dx) {
 #if _LIBCPP_STD_VER >= 23
         if constexpr (!forward_iterator<_Iterator>) {
-          __construct_at_end(std::move(__first), std::move(__last), __n);
+          __construct_at_end(std::move(__first), std::move(__last));
           std::rotate(__p, __old_last, this->__end_);
         } else
 #endif
         {
           _Iterator __m = std::next(__first, __dx);
-          __construct_at_end(__m, __last, __n - __dx);
+          __construct_at_end(__m, __last);
           if (__dx > 0) {
             __move_range(__p, __old_last, __p + __n);
             __insert_assign_n_unchecked(__first, __dx, __p);

[ldionne]

This LGTM. I like the simplification and the correctness fixes in the case of exceptions being thrown.

The commit message should mention that we technically decrease ASAN coverage while we're creating a new element, but I think that's the right tradeoff to keep the code correct and simpler.

Also, let's run the benchmarks. This touches enough important stuff that I wouldn't be surprised to see swings.

[cjdb]

Would it be possible to defer landing this patch until after #155330 has landed, please?