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gnu/gcc/4442e8b6cbffd113ec7bd25f449cc18f104f7150^!/.
commit
4442e8b6cbffd113ec7bd25f449cc18f104f7150
[log]
author
Jakub Jelinek <jakub@redhat.com>
Mon Sep 14 18:17:32 2026 +0200
committer
Jakub Jelinek <jakub@gcc.gnu.org>
Mon Sep 14 18:17:32 2026 +0200
tree
925c02e77c24c3b99e75cb7145715e1db7fecc48
parent
3f18211853985a2bedc1621c999c2ac97b184333 [diff]
libstdc++, testsuite: Implement C++26 P3450R1: Extend std::is_within_lifetime paper

Now that r17-4186 fixed constexpr evaluation of static_cast downcasts to diagnose
UB, this patch implements the C++26 P3450R1: Extend std::is_within_lifetime paper
purely in library by using __builtin_constant_p to verify if the static_cast
mandated by the standard is a constant expression.

2026-09-14  Jakub Jelinek  <jakub@redhat.com>

libstdc++-v3/
	* include/bits/version.def (within_lifetime): Change value from 202306
	to 202603.
	* include/bits/version.h: Regenerate.
	* include/std/type_traits: Implement C++26 P3450R1: Extend
	std::is_within_lifetime paper.
	(std::is_within_lifetime): Add _Up template argument defaulted to void
	and verify static_cast<const volatile _Up*>(__p) is a constant
	expression.
gcc/testsuite/
	* g++.dg/cpp26/within-lifetime1.C: Fix up C++26 paper number and name.
	* g++.dg/cpp26/within-lifetime2.C: Likewise.
	* g++.dg/cpp26/within-lifetime3.C: Likewise.
	* g++.dg/cpp26/within-lifetime4.C: Likewise.
	* g++.dg/cpp26/within-lifetime5.C: Likewise.
	* g++.dg/cpp26/within-lifetime6.C: Likewise.
	* g++.dg/cpp26/within-lifetime7.C: Likewise.
	* g++.dg/cpp26/within-lifetime8.C: Likewise.
	* g++.dg/cpp26/within-lifetime9.C: Likewise.
	* g++.dg/cpp26/within-lifetime10.C: New test.
	* g++.dg/cpp26/within-lifetime11.C: New test.
	* g++.dg/cpp26/within-lifetime12.C: New test.

Reviewed-by: Jonathan Wakely <jwakely@redhat.com>

diff --git a/gcc/testsuite/g++.dg/cpp26/within-lifetime1.C b/gcc/testsuite/g++.dg/cpp26/within-lifetime1.C
index e5ce7bd..54e2152 100644
--- a/gcc/testsuite/g++.dg/cpp26/within-lifetime1.C
+++ b/gcc/testsuite/g++.dg/cpp26/within-lifetime1.C

@@ -1,4 +1,4 @@
-// P3450R1 - Extend std::is_within_lifetime
+// P2641R4 - Checking if a union alternative is active
 // { dg-do compile { target c++20 } }
 
 #if __has_builtin(__builtin_is_within_lifetime)

diff --git a/gcc/testsuite/g++.dg/cpp26/within-lifetime10.C b/gcc/testsuite/g++.dg/cpp26/within-lifetime10.C
new file mode 100644
index 0000000..45cbbaa
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp26/within-lifetime10.C

@@ -0,0 +1,184 @@
+// P3450R1 - Extend std::is_within_lifetime
+// { dg-do compile { target c++20 } }
+
+#ifndef USE_HEADER
+#if __has_builtin(__builtin_is_within_lifetime)
+namespace std {
+  template <typename U = void, typename T>
+  consteval bool
+  is_within_lifetime (const T *p) noexcept
+  {
+    return (__builtin_is_within_lifetime (p)
+	    && __builtin_constant_p (static_cast <const volatile U *> (p)
+				     && true));
+  }
+}
+#endif
+#endif
+
+consteval int
+foo ()
+{
+  char a = 0;
+  struct B {} b;
+  struct C : B {} c;
+  struct D : C {} d;
+  struct E : B {} e;
+  if (!std::is_within_lifetime (&a))
+    return __LINE__;
+  if (!std::is_within_lifetime <char> (&a))
+    return __LINE__;
+  if (!std::is_within_lifetime <char const> (&a))
+    return __LINE__;
+  if (!std::is_within_lifetime <char volatile const> (&a))
+    return __LINE__;
+  if (!std::is_within_lifetime (&b))
+    return __LINE__;
+  if (!std::is_within_lifetime <B> (&b))
+    return __LINE__;
+  if (std::is_within_lifetime <C> (&b))
+    return __LINE__;
+  if (!std::is_within_lifetime (&c))
+    return __LINE__;
+  if (!std::is_within_lifetime <B> (&c))
+    return __LINE__;
+  if (!std::is_within_lifetime <C> (&c))
+    return __LINE__;
+  B *pb = &b;
+  B *pc = &c;
+  B *pd = &d;
+  B *pe = &e;
+  if (!std::is_within_lifetime <B> (pb))
+    return __LINE__;
+  if (!std::is_within_lifetime <B> (pc))
+    return __LINE__;
+  if (!std::is_within_lifetime <B> (pd))
+    return __LINE__;
+  if (!std::is_within_lifetime <B> (pe))
+    return __LINE__;
+  if (std::is_within_lifetime <C> (pb))
+    return __LINE__;
+  if (!std::is_within_lifetime <C> (pc))
+    return __LINE__;
+  if (!std::is_within_lifetime <C> (pd))
+    return __LINE__;
+  if (std::is_within_lifetime <C> (pe))
+    return __LINE__;
+  if (std::is_within_lifetime <D> (pb))
+    return __LINE__;
+  if (std::is_within_lifetime <D> (pc))
+    return __LINE__;
+  if (!std::is_within_lifetime <D> (pd))
+    return __LINE__;
+  if (std::is_within_lifetime <D> (pe))
+    return __LINE__;
+  if (std::is_within_lifetime <E> (pb))
+    return __LINE__;
+  if (std::is_within_lifetime <E> (pc))
+    return __LINE__;
+  if (std::is_within_lifetime <E> (pd))
+    return __LINE__;
+  if (!std::is_within_lifetime <E> (pe))
+    return __LINE__;
+  C *pf = &c;
+  C *pg = &d;
+  if (!std::is_within_lifetime <B> (pf))
+    return __LINE__;
+  if (!std::is_within_lifetime <B> (pg))
+    return __LINE__;
+  if (!std::is_within_lifetime <C> (pf))
+    return __LINE__;
+  if (!std::is_within_lifetime <C> (pg))
+    return __LINE__;
+  if (std::is_within_lifetime <D> (pf))
+    return __LINE__;
+  if (!std::is_within_lifetime <D> (pg))
+    return __LINE__;
+  return 0;
+}
+
+static_assert (foo () == 0);
+
+static constexpr char a = 0;
+static constexpr struct B { int b; } b {};
+static constexpr struct C : B {} c {};
+static constexpr struct D : C {} d {};
+static constexpr struct E : B {} e {};
+static constexpr const B *pb = &b;
+static constexpr const B *pc = &c;
+static constexpr const B *pd = &d;
+static constexpr const B *pe = &e;
+static constexpr const C *pf = &c;
+static constexpr const C *pg = &d;
+
+consteval int
+bar ()
+{
+  if (!std::is_within_lifetime (&a))
+    return __LINE__;
+  if (!std::is_within_lifetime <char> (&a))
+    return __LINE__;
+  if (!std::is_within_lifetime <char const> (&a))
+    return __LINE__;
+  if (!std::is_within_lifetime <char volatile const> (&a))
+    return __LINE__;
+  if (!std::is_within_lifetime (&b))
+    return __LINE__;
+  if (!std::is_within_lifetime <B> (&b))
+    return __LINE__;
+  if (std::is_within_lifetime <C> (&b))
+    return __LINE__;
+  if (!std::is_within_lifetime (&c))
+    return __LINE__;
+  if (!std::is_within_lifetime <B> (&c))
+    return __LINE__;
+  if (!std::is_within_lifetime <C> (&c))
+    return __LINE__;
+  if (!std::is_within_lifetime <B> (pb))
+    return __LINE__;
+  if (!std::is_within_lifetime <B> (pc))
+    return __LINE__;
+  if (!std::is_within_lifetime <B> (pd))
+    return __LINE__;
+  if (!std::is_within_lifetime <B> (pe))
+    return __LINE__;
+  if (std::is_within_lifetime <C> (pb))
+    return __LINE__;
+  if (!std::is_within_lifetime <C> (pc))
+    return __LINE__;
+  if (!std::is_within_lifetime <C> (pd))
+    return __LINE__;
+  if (std::is_within_lifetime <C> (pe))
+    return __LINE__;
+  if (std::is_within_lifetime <D> (pb))
+    return __LINE__;
+  if (std::is_within_lifetime <D> (pc))
+    return __LINE__;
+  if (!std::is_within_lifetime <D> (pd))
+    return __LINE__;
+  if (std::is_within_lifetime <D> (pe))
+    return __LINE__;
+  if (std::is_within_lifetime <E> (pb))
+    return __LINE__;
+  if (std::is_within_lifetime <E> (pc))
+    return __LINE__;
+  if (std::is_within_lifetime <E> (pd))
+    return __LINE__;
+  if (!std::is_within_lifetime <E> (pe))
+    return __LINE__;
+  if (!std::is_within_lifetime <B> (pf))
+    return __LINE__;
+  if (!std::is_within_lifetime <B> (pg))
+    return __LINE__;
+  if (!std::is_within_lifetime <C> (pf))
+    return __LINE__;
+  if (!std::is_within_lifetime <C> (pg))
+    return __LINE__;
+  if (std::is_within_lifetime <D> (pf))
+    return __LINE__;
+  if (!std::is_within_lifetime <D> (pg))
+    return __LINE__;
+  return 0;
+}
+
+static_assert (bar () == 0);

diff --git a/gcc/testsuite/g++.dg/cpp26/within-lifetime11.C b/gcc/testsuite/g++.dg/cpp26/within-lifetime11.C
new file mode 100644
index 0000000..0624abe
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp26/within-lifetime11.C

@@ -0,0 +1,6 @@
+// P3450R1 - Extend std::is_within_lifetime
+// { dg-do compile { target c++26 } }
+
+#include <type_traits>
+#define USE_HEADER
+#include "within-lifetime10.C"

diff --git a/gcc/testsuite/g++.dg/cpp26/within-lifetime12.C b/gcc/testsuite/g++.dg/cpp26/within-lifetime12.C
new file mode 100644
index 0000000..5381118
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp26/within-lifetime12.C

@@ -0,0 +1,46 @@
+// P3450R1 - Extend std::is_within_lifetime
+// { dg-do compile { target c++20 } }
+
+#if __has_builtin(__builtin_is_within_lifetime)
+namespace std {
+  template <typename U = void, typename T>
+  consteval bool
+  is_within_lifetime (const T *p) noexcept
+  {
+    return (__builtin_is_within_lifetime (p)
+	    && __builtin_constant_p (static_cast <const volatile U *> (p)
+				     && true));
+// { dg-error "invalid 'static_cast' from type 'void \\\(\\\*\\\)\\\(\\\)' to type 'const volatile void\\\*'" "" { target *-*-* } .-2 }
+// { dg-error "invalid 'static_cast' from type 'const int\\\*' to type 'const volatile long int\\\*'" "" { target *-*-* } .-3 }
+// { dg-error "invalid 'static_cast' from type 'const int\\\*' to type 'int \\\(\\\*\\\)\\\(\\\)'" "" { target *-*-* } .-4 }
+// { dg-error "'A' is an inaccessible base of 'C'" "" { target *-*-* } .-5 }
+// { dg-error "'A' is an inaccessible base of 'D'" "" { target *-*-* } .-6 }
+// { dg-error "'A' is an ambiguous base of 'E'" "" { target *-*-* } .-7 }
+// { dg-error "cannot convert from pointer to base class 'A' to pointer to derived class 'F' because the base is virtual" "" { target *-*-* } .-8 }
+  }
+}
+#endif
+
+template <typename U, typename T>
+consteval bool
+baz (T *p)
+{
+  return p ? std::is_within_lifetime <U, T> (p) : false;
+}
+
+static_assert (!baz <void, int> (nullptr));
+bool a = baz <void, void ()> (nullptr);		// { dg-message "required from here" }
+bool b = baz <long, int> (nullptr);		// { dg-message "required from here" }
+bool c = baz <int (), int> (nullptr);		// { dg-message "required from here" }
+
+struct A {};
+struct B : A {};
+struct C : protected A {};
+struct D : private A {};
+struct E : B, C, D {};
+struct F : virtual A {};
+
+bool d = baz <C, A> (nullptr);			// { dg-message "required from here" }
+bool e = baz <D, A> (nullptr);			// { dg-message "required from here" }
+bool f = baz <E, A> (nullptr);			// { dg-message "required from here" }
+bool g = baz <F, A> (nullptr);			// { dg-message "required from here" }

diff --git a/gcc/testsuite/g++.dg/cpp26/within-lifetime2.C b/gcc/testsuite/g++.dg/cpp26/within-lifetime2.C
index dc05448..469e783 100644
--- a/gcc/testsuite/g++.dg/cpp26/within-lifetime2.C
+++ b/gcc/testsuite/g++.dg/cpp26/within-lifetime2.C

@@ -1,4 +1,4 @@
-// P3450R1 - Extend std::is_within_lifetime
+// P2641R4 - Checking if a union alternative is active
 // { dg-do compile { target c++20 } }
 
 #include "../cpp2a/construct_at.h"

diff --git a/gcc/testsuite/g++.dg/cpp26/within-lifetime3.C b/gcc/testsuite/g++.dg/cpp26/within-lifetime3.C
index 36afd2e..972039c 100644
--- a/gcc/testsuite/g++.dg/cpp26/within-lifetime3.C
+++ b/gcc/testsuite/g++.dg/cpp26/within-lifetime3.C

@@ -1,4 +1,4 @@
-// P3450R1 - Extend std::is_within_lifetime
+// P2641R4 - Checking if a union alternative is active
 // { dg-do compile { target c++20 } }
 
 #include "../cpp2a/construct_at.h"

diff --git a/gcc/testsuite/g++.dg/cpp26/within-lifetime4.C b/gcc/testsuite/g++.dg/cpp26/within-lifetime4.C
index b420dea..1cb895d 100644
--- a/gcc/testsuite/g++.dg/cpp26/within-lifetime4.C
+++ b/gcc/testsuite/g++.dg/cpp26/within-lifetime4.C

@@ -1,4 +1,4 @@
-// P3450R1 - Extend std::is_within_lifetime
+// P2641R4 - Checking if a union alternative is active
 // { dg-do compile { target c++20 } }
 
 template <typename T>

diff --git a/gcc/testsuite/g++.dg/cpp26/within-lifetime5.C b/gcc/testsuite/g++.dg/cpp26/within-lifetime5.C
index 1f780cf..1b96fe2 100644
--- a/gcc/testsuite/g++.dg/cpp26/within-lifetime5.C
+++ b/gcc/testsuite/g++.dg/cpp26/within-lifetime5.C

@@ -1,4 +1,4 @@
-// P3450R1 - Extend std::is_within_lifetime
+// P2641R4 - Checking if a union alternative is active
 // { dg-do compile { target c++23 } }
 // { dg-skip-if "sizeof (bool) > 1" { powerpc-*-darwin* } }
 

diff --git a/gcc/testsuite/g++.dg/cpp26/within-lifetime6.C b/gcc/testsuite/g++.dg/cpp26/within-lifetime6.C
index 6e9ddf9..ef2544e 100644
--- a/gcc/testsuite/g++.dg/cpp26/within-lifetime6.C
+++ b/gcc/testsuite/g++.dg/cpp26/within-lifetime6.C

@@ -1,4 +1,4 @@
-// P3450R1 - Extend std::is_within_lifetime
+// P2641R4 - Checking if a union alternative is active
 // { dg-do compile { target c++26 } }
 // { dg-skip-if "sizeof (bool) > 1" { powerpc-*-darwin* } }
 

diff --git a/gcc/testsuite/g++.dg/cpp26/within-lifetime7.C b/gcc/testsuite/g++.dg/cpp26/within-lifetime7.C
index d920f5a..48098e8 100644
--- a/gcc/testsuite/g++.dg/cpp26/within-lifetime7.C
+++ b/gcc/testsuite/g++.dg/cpp26/within-lifetime7.C

@@ -1,4 +1,4 @@
-// P3450R1 - Extend std::is_within_lifetime
+// P2641R4 - Checking if a union alternative is active
 // { dg-do compile { target c++20 } }
 // { dg-options "" }
 

diff --git a/gcc/testsuite/g++.dg/cpp26/within-lifetime8.C b/gcc/testsuite/g++.dg/cpp26/within-lifetime8.C
index 98bfde2..5a28f92 100644
--- a/gcc/testsuite/g++.dg/cpp26/within-lifetime8.C
+++ b/gcc/testsuite/g++.dg/cpp26/within-lifetime8.C

@@ -1,4 +1,4 @@
-// P3450R1 - Extend std::is_within_lifetime
+// P2641R4 - Checking if a union alternative is active
 // { dg-do compile { target c++20 } }
 
 namespace std {

diff --git a/gcc/testsuite/g++.dg/cpp26/within-lifetime9.C b/gcc/testsuite/g++.dg/cpp26/within-lifetime9.C
index 905d544..d9751e4 100644
--- a/gcc/testsuite/g++.dg/cpp26/within-lifetime9.C
+++ b/gcc/testsuite/g++.dg/cpp26/within-lifetime9.C

@@ -1,4 +1,4 @@
-// P3450R1 - Extend std::is_within_lifetime
+// P2641R4 - Checking if a union alternative is active
 // { dg-do compile { target c++20 } }
 
 namespace std {

diff --git a/libstdc++-v3/include/bits/version.def b/libstdc++-v3/include/bits/version.def
index 36f8c9c..9c52358 100644
--- a/libstdc++-v3/include/bits/version.def
+++ b/libstdc++-v3/include/bits/version.def

@@ -2520,8 +2520,10 @@
 
 ftms = {
   name = within_lifetime;
+  // 202306 P2641R4 Checking if a union alternative is active
+  // 202603 P3450R1 Extend std::is_within_lifetime
   values = {
-    v = 202306;
+    v = 202603;
     cxxmin = 26;
     extra_cond = "__has_builtin(__builtin_is_within_lifetime)";
   };

diff --git a/libstdc++-v3/include/bits/version.h b/libstdc++-v3/include/bits/version.h
index e79ea50..e000305 100644
--- a/libstdc++-v3/include/bits/version.h
+++ b/libstdc++-v3/include/bits/version.h

@@ -2776,9 +2776,9 @@
 
 #if !defined(__cpp_lib_within_lifetime)
 # if (__cplusplus >  202302L) && (__has_builtin(__builtin_is_within_lifetime))
-#  define __glibcxx_within_lifetime 202306L
+#  define __glibcxx_within_lifetime 202603L
 #  if defined(__glibcxx_want_all) || defined(__glibcxx_want_within_lifetime)
-#   define __cpp_lib_within_lifetime 202306L
+#   define __cpp_lib_within_lifetime 202603L
 #  endif
 # endif
 #endif /* !defined(__cpp_lib_within_lifetime) */

diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index 921ef28..83dbad1 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits

@@ -4401,11 +4401,15 @@
     };
 #endif // C++11
 
-#if __cpp_lib_within_lifetime >= 202306L // C++ >= 26
-  template<typename _Tp>
+#if __cpp_lib_within_lifetime >= 202603L // C++ >= 26
+  template<typename _Up = void, typename _Tp>
     consteval bool
     is_within_lifetime(const _Tp* __p) noexcept
-    { return __builtin_is_within_lifetime (__p); }
+    {
+      return (__builtin_is_within_lifetime (__p)
+	      && __builtin_constant_p(static_cast<const volatile _Up*>(__p)
+				      && true));
+    }
 #endif
 
   /// @} group metaprogramming