From 065dddc6e07a917c57c7955db13b1fe77abbcabc Mon Sep 17 00:00:00 2001
From: Paul Keir <paul.keir@uws.ac.uk>
Date: Mon, 12 Feb 2024 18:15:49 +0000
Subject: [PATCH] libstdc++: Fix constexpr basic_string union member [PR113294]
A call to `basic_string::clear()` in the std::string move assignment
operator leads to a constexpr error from an access of inactive union
member `_M_local_buf` in the added test (`test_move()`). Changing
`__str._M_local_buf` to `__str._M_use_local_data()` in
`operator=(basic_string&& __str)` fixes this.
PR libstdc++/113294
libstdc++-v3/ChangeLog:
* include/bits/basic_string.h (basic_string::operator=): Use
_M_use_local_data() instead of _M_local_buf on the moved-from
string.
* testsuite/21_strings/basic_string/modifiers/constexpr.cc
(test_move): New test.
Signed-off-by: Paul Keir <paul.keir@uws.ac.uk>
Reviewed-by: Patrick Palka <ppalka@redhat.com>
Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
---
libstdc++-v3/include/bits/basic_string.h | 2 +-
.../21_strings/basic_string/modifiers/constexpr.cc | 14 ++++++++++++++
2 files changed, 15 insertions(+), 1 deletion(-)
diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h
index 43efc99bea9d..8a695a494efd 100644
--- a/libstdc++-v3/include/bits/basic_string.h
+++ b/libstdc++-v3/include/bits/basic_string.h
@@ -909,7 +909,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
__str._M_capacity(__capacity);
}
else
- __str._M_data(__str._M_local_buf);
+ __str._M_data(__str._M_use_local_data());
}
else // Need to do a deep copy
assign(__str);
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/modifiers/constexpr.cc b/libstdc++-v3/testsuite/21_strings/basic_string/modifiers/constexpr.cc
index 0e28a6d44872..d7022af3cabe 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string/modifiers/constexpr.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string/modifiers/constexpr.cc
@@ -50,3 +50,17 @@ test_erasure()
}
static_assert( test_erasure() );
+
+constexpr bool
+test_move()
+{
+ // PR libstdc++/113294
+ std::string s1;
+ std::string s2 = "1234567890123456"; // 16 chars: more than _S_local_capacity
+ s1 = std::move(s2);
+ VERIFY( s1 == "1234567890123456" );
+
+ return true;
+}
+
+static_assert( test_move() );
--
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