libstdc++: Replace use of __mindist in ranges::uninitialized_xxx algos [PR101587]

In r15-8980-gf4b6acfc36fb1f I introduced a new function object for
finding the smaller of two distances. In bugzilla Hewill Kang pointed
out that we still need to explicitly convert the result back to the
right difference type, because the result might be an integer-like class
type that doesn't convert to an integral type explicitly.

Rather than doing that conversion in the __mindist function object, I
think it's simpler to remove it again and just do a comparison and
assignment. We always want the result to have a specific type, so we can
just check if the value of the other type is smaller, and then convert
that to the other type if so.

libstdc++-v3/ChangeLog:

	PR libstdc++/101587
	* include/bits/ranges_uninitialized.h (__detail::__mindist):
	Remove.
	(ranges::uninitialized_copy, ranges::uninitialized_copy_n)
	(ranges::uninitialized_move, ranges::uninitialized_move_n): Use
	comparison and assignment instead of __mindist.
	* testsuite/20_util/specialized_algorithms/uninitialized_copy/constrained.cc:
	Check with ranges that use integer-like class type for
	difference type.
	* testsuite/20_util/specialized_algorithms/uninitialized_move/constrained.cc:
	Likewise.

Reviewed-by: Tomasz Kaminski <tkaminsk@redhat.com>
Reviewed-by: Hewill Kang <hewillk@gmail.com>

3 files changed, 71 insertions, 34 deletions

diff --git a/libstdc++-v3/include/bits/ranges_uninitialized.h b/libstdc++-v3/include/bits/ranges_uninitialized.h
index b558007..12a714b 100644
--- a/libstdc++-v3/include/bits/ranges_uninitialized.h
+++ b/libstdc++-v3/include/bits/ranges_uninitialized.h
@@ -263,26 +263,6 @@ namespace ranges
   inline constexpr __uninitialized_value_construct_n_fn
     uninitialized_value_construct_n;
 
-  namespace __detail
-  {
-    // This is only intended for finding smaller iterator differences below,
-    // not as a general purpose replacement for std::min.
-    struct __mindist_fn
-    {
-      template<typename _Dp1, typename _Dp2>
-	constexpr common_type_t<_Dp1, _Dp2>
-	operator()(_Dp1 __d1, _Dp2 __d2) const noexcept
-	{
-	  // Every C++20 iterator I satisfies weakly_incrementable<I> which
-	  // requires signed-integer-like<iter_difference_t<I>>.
-	  static_assert(std::__detail::__is_signed_integer_like<_Dp1>);
-	  static_assert(std::__detail::__is_signed_integer_like<_Dp2>);
-	  return std::min<common_type_t<_Dp1, _Dp2>>(__d1, __d2);
-	}
-    };
-    inline constexpr __mindist_fn __mindist{};
-  }
-
   template<typename _Iter, typename _Out>
     using uninitialized_copy_result = in_out_result<_Iter, _Out>;
 
@@ -305,10 +285,10 @@ namespace ranges
 		      && is_trivially_assignable_v<_OutType&,
 						 iter_reference_t<_Iter>>)
 	  {
-	    auto __d1 = __ilast - __ifirst;
-	    auto __d2 = __olast - __ofirst;
-	    return ranges::copy_n(std::move(__ifirst),
-				  __detail::__mindist(__d1, __d2), __ofirst);
+	    auto __d = __ilast - __ifirst;
+	    if (auto __d2 = __olast - __ofirst; __d2 < __d)
+	      __d = static_cast<iter_difference_t<_Iter>>(__d2);
+	    return ranges::copy_n(std::move(__ifirst), __d, __ofirst);
 	  }
 	else
 	  {
@@ -356,9 +336,9 @@ namespace ranges
 		      && is_trivially_assignable_v<_OutType&,
 						 iter_reference_t<_Iter>>)
 	  {
-	    auto __d = __olast - __ofirst;
-	    return ranges::copy_n(std::move(__ifirst),
-				  __detail::__mindist(__n, __d), __ofirst);
+	    if (auto __d = __olast - __ofirst; __d < __n)
+	      __n = static_cast<iter_difference_t<_Iter>>(__d);
+	    return ranges::copy_n(std::move(__ifirst), __n, __ofirst);
 	  }
 	else
 	  {
@@ -397,11 +377,12 @@ namespace ranges
 		      && is_trivially_assignable_v<_OutType&,
 						 iter_rvalue_reference_t<_Iter>>)
 	  {
-	    auto __d1 = __ilast - __ifirst;
-	    auto __d2 = __olast - __ofirst;
+	    auto __d = __ilast - __ifirst;
+	    if (auto __d2 = __olast - __ofirst; __d2 < __d)
+	      __d = static_cast<iter_difference_t<_Iter>>(__d2);
 	    auto [__in, __out]
 	      = ranges::copy_n(std::make_move_iterator(std::move(__ifirst)),
-			       __detail::__mindist(__d1, __d2), __ofirst);
+			       __d, __ofirst);
 	    return {std::move(__in).base(), __out};
 	  }
 	else
@@ -452,10 +433,11 @@ namespace ranges
 		      && is_trivially_assignable_v<_OutType&,
 						 iter_rvalue_reference_t<_Iter>>)
 	  {
-	    auto __d = __olast - __ofirst;
+	    if (auto __d = __olast - __ofirst; __d < __n)
+	      __n = static_cast<iter_difference_t<_Iter>>(__d);
 	    auto [__in, __out]
 	      = ranges::copy_n(std::make_move_iterator(std::move(__ifirst)),
-			       __detail::__mindist(__n, __d), __ofirst);
+			       __n, __ofirst);
 	    return {std::move(__in).base(), __out};
 	  }
 	else
diff --git a/libstdc++-v3/testsuite/20_util/specialized_algorithms/uninitialized_copy/constrained.cc b/libstdc++-v3/testsuite/20_util/specialized_algorithms/uninitialized_copy/constrained.cc
index af3b733..5dff0da 100644
--- a/libstdc++-v3/testsuite/20_util/specialized_algorithms/uninitialized_copy/constrained.cc
+++ b/libstdc++-v3/testsuite/20_util/specialized_algorithms/uninitialized_copy/constrained.cc
@@ -178,12 +178,40 @@ test03()
 void
 test_pr101587()
 {
-  short in[1];
+  short in[1]{};
   __gnu_test::test_contiguous_range r(in); // difference_type is integer-like
   long out[1];
   std::span<long> o(out); // difference_type is ptrdiff_t
   ranges::uninitialized_copy(r, o);
   ranges::uninitialized_copy_n(ranges::begin(r), 0, o.begin(), o.end());
+
+  // iterator that has an integer-like class type for difference_type
+  struct Iter
+  {
+    using value_type = long;
+    using difference_type = std::ranges::__detail::__max_diff_type;
+
+    long& operator*() const { return *p; }
+
+    Iter& operator++() { ++p; return *this; }
+    Iter operator++(int) { return Iter{p++}; }
+
+    difference_type operator-(Iter i) const { return p - i.p; }
+    bool operator==(const Iter&) const = default;
+
+    long* p = nullptr;
+  };
+  static_assert(std::sized_sentinel_for<Iter, Iter>);
+
+  std::ranges::subrange<Iter> rmax(Iter{out+0}, Iter{out+1});
+  // Check with integer-like class type for output range:
+  std::ranges::uninitialized_copy(in, rmax);
+  std::ranges::uninitialized_copy_n(in+0, 1, rmax.begin(), rmax.end());
+
+  int to[1];
+  // And for input range:
+  std::ranges::uninitialized_copy(rmax, to);
+  std::ranges::uninitialized_copy_n(rmax.begin(), 1, to+0, to+1);
 }
 
 int
diff --git a/libstdc++-v3/testsuite/20_util/specialized_algorithms/uninitialized_move/constrained.cc b/libstdc++-v3/testsuite/20_util/specialized_algorithms/uninitialized_move/constrained.cc
index fe82d1f1..3e81244 100644
--- a/libstdc++-v3/testsuite/20_util/specialized_algorithms/uninitialized_move/constrained.cc
+++ b/libstdc++-v3/testsuite/20_util/specialized_algorithms/uninitialized_move/constrained.cc
@@ -188,12 +188,39 @@ test03()
 void
 test_pr101587()
 {
-  short in[1];
+  short in[1]{};
   __gnu_test::test_contiguous_range r(in); // difference_type is integer-like
   long out[1];
   std::span<long> o(out); // difference_type is ptrdiff_t
   ranges::uninitialized_move(r, o);
   ranges::uninitialized_move_n(ranges::begin(r), 0, o.begin(), o.end());
+
+  struct Iter
+  {
+    using value_type = long;
+    using difference_type = std::ranges::__detail::__max_diff_type;
+
+    long& operator*() const { return *p; }
+
+    Iter& operator++() { ++p; return *this; }
+    Iter operator++(int) { return Iter{p++}; }
+
+    difference_type operator-(Iter i) const { return p - i.p; }
+    bool operator==(const Iter&) const = default;
+
+    long* p = nullptr;
+  };
+  static_assert(std::sized_sentinel_for<Iter, Iter>);
+
+  std::ranges::subrange<Iter> rmax(Iter{out+0}, Iter{out+1});
+  // Check with integer-like class type for output range:
+  std::ranges::uninitialized_move(in, rmax);
+  std::ranges::uninitialized_move_n(in+0, 1, rmax.begin(), rmax.end());
+
+  int to[1];
+  // And for input range:
+  std::ranges::uninitialized_copy(rmax, to);
+  std::ranges::uninitialized_copy_n(rmax.begin(), 1, to+0, to+1);
 }
 
 int