[gcc/devel/c++-coroutines] libstdc++: Fix use of is_nothrow_assignable_v in <bits/ranges_uninitialized.h>

[Iain D Sandoe]

https://gcc.gnu.org/g:05779e2c89e06d09a6b685797e87723f7906a5ce

commit 05779e2c89e06d09a6b685797e87723f7906a5ce
Author: Patrick Palka <ppalka@redhat.com>
Date:   Mon Mar 2 19:39:13 2020 -0500

    libstdc++: Fix use of is_nothrow_assignable_v in <bits/ranges_uninitialized.h>
    
    We are passing a value type as the first argument to is_nothrow_assignable_v,
    but the result of that is inevitably false.  Since this predicate is a part of
    the condition that guards the corresponding optimizations for these algorithms,
    this bug means these optimizations are never used.  We should be passing a
    reference type to is_nothrow_assignable_v instead.
    
    libstdc++-v3/ChangeLog:
    
    	* include/bits/ranges_uninitialized.h
    	(uninitialized_copy_fn::operator()): Pass a reference type as the first
    	argument to is_nothrow_assignable_v.
    	(uninitialized_copy_fn::operator()): Likewise.
    	(uninitialized_move_fn::operator()): Likewise.  Return an in_out_result
    	with the input iterator stripped of its move_iterator.
    	(uninitialized_move_n_fn::operator()): Likewise.
    	(uninitialized_fill_fn::operator()): Pass a reference type as the first
    	argument to is_nothrow_assignable_v.
    	(uninitialized_fill_n_fn::operator()): Likewise.

Diff:
---
 libstdc++-v3/ChangeLog                           | 13 +++++++++++++
 libstdc++-v3/include/bits/ranges_uninitialized.h | 24 ++++++++++++++----------
 2 files changed, 27 insertions(+), 10 deletions(-)

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 640c5be..45ff06d 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,16 @@
+2020-03-04  Patrick Palka  <ppalka@redhat.com>
+
+	* include/bits/ranges_uninitialized.h
+	(uninitialized_copy_fn::operator()): Pass a reference type as the first
+	argument to is_nothrow_assignable_v.
+	(uninitialized_copy_fn::operator()): Likewise.
+	(uninitialized_move_fn::operator()): Likewise.  Return an in_out_result
+	with the input iterator stripped of its move_iterator.
+	(uninitialized_move_n_fn::operator()): Likewise.
+	(uninitialized_fill_fn::operator()): Pass a reference type as the first
+	argument to is_nothrow_assignable_v.
+	(uninitialized_fill_n_fn::operator()): Likewise.
+
 2020-03-03  Jonathan Wakely  <jwakely@redhat.com>
 
 	PR libstdc++/94013
diff --git a/libstdc++-v3/include/bits/ranges_uninitialized.h b/libstdc++-v3/include/bits/ranges_uninitialized.h
index 01e1cad..f97a07a 100644
--- a/libstdc++-v3/include/bits/ranges_uninitialized.h
+++ b/libstdc++-v3/include/bits/ranges_uninitialized.h
@@ -269,7 +269,7 @@ namespace ranges
 	if constexpr (sized_sentinel_for<_ISent, _Iter>
 		      && sized_sentinel_for<_OSent, _Out>
 		      && is_trivial_v<_OutType>
-		      && is_nothrow_assignable_v<_OutType,
+		      && is_nothrow_assignable_v<_OutType&,
 						 iter_reference_t<_Iter>>)
 	  {
 	    auto __d1 = ranges::distance(__ifirst, __ilast);
@@ -316,7 +316,7 @@ namespace ranges
 	using _OutType = remove_reference_t<iter_reference_t<_Out>>;
 	if constexpr (sized_sentinel_for<_Sent, _Out>
 		      && is_trivial_v<_OutType>
-		      && is_nothrow_assignable_v<_OutType,
+		      && is_nothrow_assignable_v<_OutType&,
 						 iter_reference_t<_Iter>>)
 	  {
 	    auto __d = ranges::distance(__ofirst, __olast);
@@ -354,13 +354,15 @@ namespace ranges
 	if constexpr (sized_sentinel_for<_ISent, _Iter>
 		      && sized_sentinel_for<_OSent, _Out>
 		      && is_trivial_v<_OutType>
-		      && is_nothrow_assignable_v<_OutType,
+		      && is_nothrow_assignable_v<_OutType&,
 						 iter_rvalue_reference_t<_Iter>>)
 	  {
 	    auto __d1 = ranges::distance(__ifirst, __ilast);
 	    auto __d2 = ranges::distance(__ofirst, __olast);
-	    return ranges::copy_n(std::make_move_iterator(__ifirst),
-				  std::min(__d1, __d2), __ofirst);
+	    auto [__in, __out]
+	      = ranges::copy_n(std::make_move_iterator(__ifirst),
+			       std::min(__d1, __d2), __ofirst);
+	    return {std::move(__in).base(), __out};
 	  }
 	else
 	  {
@@ -404,12 +406,14 @@ namespace ranges
 	using _OutType = remove_reference_t<iter_reference_t<_Out>>;
 	if constexpr (sized_sentinel_for<_Sent, _Out>
 		      && is_trivial_v<_OutType>
-		      && is_nothrow_assignable_v<_OutType,
+		      && is_nothrow_assignable_v<_OutType&,
 						 iter_rvalue_reference_t<_Iter>>)
 	  {
 	    auto __d = ranges::distance(__ofirst, __olast);
-	    return ranges::copy_n(std::make_move_iterator(__ifirst),
-				  std::min(__n, __d), __ofirst);
+	    auto [__in, __out]
+	      = ranges::copy_n(std::make_move_iterator(__ifirst),
+			       std::min(__n, __d), __ofirst);
+	    return {std::move(__in).base(), __out};
 	  }
 	else
 	  {
@@ -436,7 +440,7 @@ namespace ranges
       {
 	using _ValueType = remove_reference_t<iter_reference_t<_Iter>>;
 	if constexpr (is_trivial_v<_ValueType>
-		      && is_nothrow_assignable_v<_ValueType, const _Tp&>)
+		      && is_nothrow_assignable_v<_ValueType&, const _Tp&>)
 	  return ranges::fill(__first, __last, __x);
 	else
 	  {
@@ -469,7 +473,7 @@ namespace ranges
       {
 	using _ValueType = remove_reference_t<iter_reference_t<_Iter>>;
 	if constexpr (is_trivial_v<_ValueType>
-		      && is_nothrow_assignable_v<_ValueType, const _Tp&>)
+		      && is_nothrow_assignable_v<_ValueType&, const _Tp&>)
 	  return ranges::fill_n(__first, __n, __x);
 	else
 	  {