[libc++] Use __unwrap_iter_impl for both unwrapping and rewrapping

Reviewed By: ldionne, #libc

Spies: arichardson, sstefan1, libcxx-commits

Differential Revision: https://reviews.llvm.org/D129039

libcxx/include/__algorithm/unwrap_iter.h

@@ -12,6 +12,7 @@
 #include <__config>
 #include <__iterator/iterator_traits.h>
 #include <__memory/pointer_traits.h>
+#include <__utility/move.h>
 #include <type_traits>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
@@ -20,77 +21,50 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-// The job of __unwrap_iter is to lower contiguous iterators (such as
+// TODO: Change the name of __unwrap_iter_impl to something more appropriate
-// vector<T>::iterator) into pointers, to reduce the number of template
+// The job of __unwrap_iter is to remove iterator wrappers (like reverse_iterator or __wrap_iter),
-// instantiations and to enable pointer-based optimizations e.g. in std::copy.
+// to reduce the number of template instantiations and to enable pointer-based optimizations e.g. in std::copy.
-// For iterators that are not contiguous, it must be a no-op.
 // In debug mode, we don't do this.
 //
-// __unwrap_iter is non-constexpr for user-defined iterators whose
-// `to_address` and/or `operator->` is non-constexpr. This is okay; but we
-// try to avoid doing __unwrap_iter in constant-evaluated contexts anyway.
-//
 // Some algorithms (e.g. std::copy, but not std::sort) need to convert an
-// "unwrapped" result back into a contiguous iterator. Since contiguous iterators
+// "unwrapped" result back into the original iterator type. Doing that is the job of __rewrap_iter.
-// are random-access, we can do this portably using iterator arithmetic; this
-// is the job of __rewrap_iter.
 
+// Default case - we can't unwrap anything
 template <class _Iter, bool = __is_cpp17_contiguous_iterator<_Iter>::value>
 struct __unwrap_iter_impl {
-    static _LIBCPP_CONSTEXPR _Iter
+  static _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _Iter __rewrap(_Iter, _Iter __iter) { return __iter; }
-    __apply(_Iter __i) _NOEXCEPT {
+  static _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _Iter __unwrap(_Iter __i) _NOEXCEPT { return __i; }
-        return __i;
-    }
 };
 
 #ifndef _LIBCPP_ENABLE_DEBUG_MODE
 
+// It's a contiguous iterator, so we can use a raw pointer instead
 template <class _Iter>
 struct __unwrap_iter_impl<_Iter, true> {
-    static _LIBCPP_CONSTEXPR decltype(_VSTD::__to_address(declval<_Iter>()))
+  using _ToAddressT = decltype(std::__to_address(std::declval<_Iter>()));
-    __apply(_Iter __i) _NOEXCEPT {
+
-        return _VSTD::__to_address(__i);
+  static _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _Iter __rewrap(_Iter __orig_iter, _ToAddressT __unwrapped_iter) {
+    return __orig_iter + (__unwrapped_iter - std::__to_address(__orig_iter));
+  }
+
+  static _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _ToAddressT __unwrap(_Iter __i) _NOEXCEPT {
+    return std::__to_address(__i);
   }
 };
 
 #endif // !_LIBCPP_ENABLE_DEBUG_MODE
 
-template<class _Iter, class _Impl = __unwrap_iter_impl<_Iter> >
+template<class _Iter,
-inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
+         class _Impl = __unwrap_iter_impl<_Iter>,
-decltype(_Impl::__apply(declval<_Iter>()))
+         __enable_if_t<is_copy_constructible<_Iter>::value, int> = 0>
-__unwrap_iter(_Iter __i) _NOEXCEPT
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX11
-{
+decltype(_Impl::__unwrap(std::declval<_Iter>())) __unwrap_iter(_Iter __i) _NOEXCEPT {
-    return _Impl::__apply(__i);
+  return _Impl::__unwrap(__i);
 }
 
-template <class _OrigIter, class _UnwrappedIter>
+template <class _OrigIter, class _Iter, class _Impl = __unwrap_iter_impl<_OrigIter> >
-struct __rewrap_iter_impl {
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _OrigIter __rewrap_iter(_OrigIter __orig_iter, _Iter __iter) _NOEXCEPT {
-  static _LIBCPP_CONSTEXPR _OrigIter __apply(_OrigIter __first, _UnwrappedIter __result) {
+  return _Impl::__rewrap(std::move(__orig_iter), std::move(__iter));
-    // Precondition: __result is reachable from __first
-    // Precondition: _OrigIter is a contiguous iterator
-    return __first + (__result - std::__unwrap_iter(__first));
-  }
-};
-
-template <class _OrigIter>
-struct __rewrap_iter_impl<_OrigIter, _OrigIter> {
-  static _LIBCPP_CONSTEXPR _OrigIter __apply(_OrigIter, _OrigIter __result) {
-    return __result;
-  }
-};
-
-template<class _OrigIter>
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR
-_OrigIter __rewrap_iter(_OrigIter, _OrigIter __result)
-{
-    return __result;
-}
-
-template<class _OrigIter, class _UnwrappedIter, class _Impl = __rewrap_iter_impl<_OrigIter, _UnwrappedIter> >
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR
-_OrigIter __rewrap_iter(_OrigIter __first, _UnwrappedIter __result)
-{
-  return _Impl::__apply(__first, __result);
 }
 
 _LIBCPP_END_NAMESPACE_STD

libcxx/include/__iterator/reverse_iterator.h

@@ -332,41 +332,16 @@ using _ReverseWrapper = reverse_iterator<reverse_iterator<_Iter> >;
 
 template <class _Iter, bool __b>
 struct __unwrap_iter_impl<_ReverseWrapper<_Iter>, __b> {
-  static _LIBCPP_CONSTEXPR decltype(std::__unwrap_iter(std::declval<_Iter>()))
+  using _UnwrappedIter = decltype(__unwrap_iter_impl<_Iter>::__unwrap(std::declval<_Iter>()));
-  __apply(_ReverseWrapper<_Iter> __i) _NOEXCEPT {
-    return std::__unwrap_iter(__i.base().base());
-  }
-};
 
-template <class _OrigIter, class _UnwrappedIter>
+  static _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _ReverseWrapper<_Iter>
-struct __rewrap_iter_impl<_ReverseWrapper<_OrigIter>, _UnwrappedIter> {
+  __rewrap(_ReverseWrapper<_Iter> __orig_iter, _UnwrappedIter __unwrapped_iter) {
-  template <class _Iter>
+    return _ReverseWrapper<_Iter>(
-  struct _ReverseWrapperCount {
+        reverse_iterator<_Iter>(__unwrap_iter_impl<_Iter>::__rewrap(__orig_iter.base().base(), __unwrapped_iter)));
-    static _LIBCPP_CONSTEXPR const size_t value = 1;
-  };
-
-  template <class _Iter>
-  struct _ReverseWrapperCount<_ReverseWrapper<_Iter> > {
-    static _LIBCPP_CONSTEXPR const size_t value = 1 + _ReverseWrapperCount<_Iter>::value;
-  };
-
-  template <size_t _RewrapCount, class _OIter, class _UIter, __enable_if_t<_RewrapCount != 0, int> = 0>
-  _LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR _ReverseWrapper<_OIter> __rewrap(_ReverseWrapper<_OIter> __iter1,
-                                                                                  _UIter __iter2) {
-    return _ReverseWrapper<_OIter>(
-        reverse_iterator<_OIter>(__rewrap<_RewrapCount - 1>(__iter1.base().base(), __iter2)));
   }
 
-  template <size_t _RewrapCount, class _OIter, class _UIter, __enable_if_t<_RewrapCount == 0, int> = 0>
+  static _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _UnwrappedIter __unwrap(_ReverseWrapper<_Iter> __i) _NOEXCEPT {
-  _LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR decltype(std::__rewrap_iter(std::declval<_OIter>(),
+    return __unwrap_iter_impl<_Iter>::__unwrap(__i.base().base());
-                                                                             std::declval<_UIter>()))
-  __rewrap(_OIter __iter1, _UIter __iter2) {
-    return std::__rewrap_iter(__iter1, __iter2);
-  }
-
-  _LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR _ReverseWrapper<_OrigIter> __apply(_ReverseWrapper<_OrigIter> __iter1,
-                                                                                    _UnwrappedIter __iter2) {
-    return __rewrap<_ReverseWrapperCount<_OrigIter>::value>(__iter1, __iter2);
   }
 };
 

libcxx/utils/libcxx/test/params.py

@@ -38,6 +38,9 @@ _warningFlags = [
   # TODO(mordante) investigate a solution for this issue.
   '-Wno-tautological-compare',
 
+  # -Wstringop-overread seems to be a bit buggy currently
+  '-Wno-stringop-overread',
+
   # These warnings should be enabled in order to support the MSVC
   # team using the test suite; They enable the warnings below and
   # expect the test suite to be clean.