https://gcc.gnu.org/g:b51ca7d2f548ffdad03fa779e3ff7bcc3441ff03
commit r16-2770-gb51ca7d2f548ffdad03fa779e3ff7bcc3441ff03
Author: Patrick Palka <ppa...@redhat.com>
Date: Mon Aug 4 16:43:33 2025 -0400
c++: constexpr evaluation of abi::__dynamic_cast [PR120620]
r13-3299 changed our internal declaration of __dynamic_cast to reside
inside the abi/__cxxabiv1:: namespace instead of the global namespace,
matching the real declaration. This inadvertently made us now attempt
constexpr evaluation of user-written calls to abi::__dynamic_cast since
cxx_dynamic_cast_fn_p now also returns true for them, but we're not
prepared to handle arbitrary calls to __dynamic_cast, and therefore ICE.
This patch restores cxx_dynamic_cast_fn_p to return true only for
synthesized calls to __dynamic_cast, which can be distinguished by
DECL_ARTIFICIAL, since apparently the synthesized declaration of
__dynamic_cast doesn't get merged with the actual declaration.
PR c++/120620
gcc/cp/ChangeLog:
* constexpr.cc (cxx_dynamic_cast_fn_p): Return true only
for synthesized __dynamic_cast.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/constexpr-dynamic19.C: New test.
* g++.dg/cpp2a/constexpr-dynamic1a.C: New test.
Reviewed-by: Jason Merrill <ja...@redhat.com>
Diff:
---
gcc/cp/constexpr.cc | 6 +++++-
gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic19.C | 10 ++++++++++
gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic1a.C | 6 ++++++
3 files changed, 21 insertions(+), 1 deletion(-)
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index be24ae2feda6..142579a91029 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -3240,7 +3240,11 @@ cxx_dynamic_cast_fn_p (tree fndecl)
{
return (cxx_dialect >= cxx20
&& id_equal (DECL_NAME (fndecl), "__dynamic_cast")
- && CP_DECL_CONTEXT (fndecl) == abi_node);
+ && CP_DECL_CONTEXT (fndecl) == abi_node
+ /* Only consider implementation-detail __dynamic_cast calls that
+ correspond to a dynamic_cast, and ignore direct calls to
+ abi::__dynamic_cast. */
+ && DECL_ARTIFICIAL (fndecl));
}
/* Often, we have an expression in the form of address + offset, e.g.
diff --git a/gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic19.C
b/gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic19.C
new file mode 100644
index 000000000000..27d167cebc35
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic19.C
@@ -0,0 +1,10 @@
+// PR c++/120620
+// { dg-do compile }
+
+#include <cxxabi.h>
+
+struct A* a;
+
+void f() {
+ void* const p = abi::__dynamic_cast(&a, 0, 0, 42);
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic1a.C
b/gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic1a.C
new file mode 100644
index 000000000000..4077a47055c7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/constexpr-dynamic1a.C
@@ -0,0 +1,6 @@
+// Test that including <cxxabi.h>, whence the actual abi:__dynamic_cast
+// is declared, doesn't affect our constexpr dynamic_cast handling.
+// { dg-do compile { target c++20 } }
+
+#include <cxxabi.h>
+#include "constexpr-dynamic1.C"
