[gcc r12-8936] libstdc++: Remove unnecessary variant member in std::expected

[Jonathan Wakely]

https://gcc.gnu.org/g:377f954242420c6bba380db400bf89ec677647bc

commit r12-8936-g377f954242420c6bba380db400bf89ec677647bc
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Nov 1 13:47:24 2022 +0000

    libstdc++: Remove unnecessary variant member in std::expected
    
    Hui Xie pointed out that we don't need a dummy member in the union,
    because all constructors always initialize either _M_val or _M_unex.
    
    We still need the _M_void member of the expected<void, E>
    specialization, because the constructor has to initialize something when
    not using the _M_unex member.
    
    libstdc++-v3/ChangeLog:
    
            * include/std/expected (expected::_M_invalid): Remove.
    
    (cherry picked from commit f4874691812bc20e3d8e3302db439c27f30c472c)

Diff:
---
 libstdc++-v3/include/std/expected | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/libstdc++-v3/include/std/expected b/libstdc++-v3/include/std/expected
index 3ee13aa95f6..e491ce41591 100644
--- a/libstdc++-v3/include/std/expected
+++ b/libstdc++-v3/include/std/expected
@@ -359,7 +359,7 @@ namespace __expected
       requires is_copy_constructible_v<_Tp> && is_copy_constructible_v<_Er>
       && (!is_trivially_copy_constructible_v<_Tp>
 	  || !is_trivially_copy_constructible_v<_Er>)
-      : _M_invalid(), _M_has_value(__x._M_has_value)
+      : _M_has_value(__x._M_has_value)
       {
 	if (_M_has_value)
 	  std::construct_at(__builtin_addressof(_M_val), __x._M_val);
@@ -376,7 +376,7 @@ namespace __expected
       requires is_move_constructible_v<_Tp> && is_move_constructible_v<_Er>
       && (!is_trivially_move_constructible_v<_Tp>
 	  || !is_trivially_move_constructible_v<_Er>)
-      : _M_invalid(), _M_has_value(__x._M_has_value)
+      : _M_has_value(__x._M_has_value)
       {
 	if (_M_has_value)
 	  std::construct_at(__builtin_addressof(_M_val),
@@ -394,7 +394,7 @@ namespace __expected
 	expected(const expected<_Up, _Gr>& __x)
 	noexcept(__and_v<is_nothrow_constructible<_Tp, const _Up&>,
 			 is_nothrow_constructible<_Er, const _Gr&>>)
-	: _M_invalid(), _M_has_value(__x._M_has_value)
+	: _M_has_value(__x._M_has_value)
 	{
 	  if (_M_has_value)
 	    std::construct_at(__builtin_addressof(_M_val), __x._M_val);
@@ -410,7 +410,7 @@ namespace __expected
 	expected(expected<_Up, _Gr>&& __x)
 	noexcept(__and_v<is_nothrow_constructible<_Tp, _Up>,
 			 is_nothrow_constructible<_Er, _Gr>>)
-	: _M_invalid(), _M_has_value(__x._M_has_value)
+	: _M_has_value(__x._M_has_value)
 	{
 	  if (_M_has_value)
 	    std::construct_at(__builtin_addressof(_M_val),
@@ -890,7 +890,6 @@ namespace __expected
       }
 
       union {
-	struct { } _M_invalid;
 	_Tp _M_val;
 	_Er _M_unex;
       };