According to [basic.start.static]/2 and [expr.const]/2, a variable
with static storage duration initialized with a constant initializer
has constant initialization, and such an initializer is manifestly
constant-evaluated.
We're already getting this right with copy initialization because in
that case check_initializer would consistently call store_init_value
(which for TREE_STATIC variables calls fold_non_dependent_init with
m_c_e=true).
But for direct (or default) initialization, we don't always call
store_init_value. We instead however always call maybe_constant_init
from expand_default_init[1], albeit with m_c_e=false which means we
don't always get the "manifestly constant-evaluated" part right for
copy-init.
This patch fixes this by simply passing m_c_e=true to this call to
maybe_constant_init for static storage duration variables, mirroring
what store_init_value basically does.
[1]: this maybe_constant_init call isn't reached in the copy-init
case because there init is a CONSTRUCTOR rather than a TREE_LIST so
expand_default_init exits early returning an INIT_EXPR. This INIT_EXPR
is ultimately what causes us to consistently hit the store_init_value
code path from check_initializer in the copy-init case.
Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk? Would it be suitable to backport this to the 12 branch since
it should only affect C++20 code?
PR c++/108243
gcc/cp/ChangeLog:
* init.cc (expand_default_init): Pass m_c_e=true instead of
=false to maybe_constant_init when initializing a variable
with static storage duration.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/is-constant-evaluated14.C: New test.
---
gcc/cp/init.cc | 5 +-
.../g++.dg/cpp2a/is-constant-evaluated14.C | 140 ++++++++++++++++++
2 files changed, 144 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated14.C
diff --git a/gcc/cp/init.cc b/gcc/cp/init.cc
index 52e96fbe590..705a5b3bdb6 100644
--- a/gcc/cp/init.cc
+++ b/gcc/cp/init.cc
@@ -2203,7 +2203,10 @@ expand_default_init (tree binfo, tree true_exp, tree
exp, tree init, int flags,
tree fn = get_callee_fndecl (rval);
if (fn && DECL_DECLARED_CONSTEXPR_P (fn))
{
- tree e = maybe_constant_init (rval, exp);
+ bool manifestly_const_eval = false;
+ if (VAR_P (exp) && TREE_STATIC (exp))
+ manifestly_const_eval = true;
+ tree e = maybe_constant_init (rval, exp, manifestly_const_eval);
if (TREE_CONSTANT (e))
rval = cp_build_init_expr (exp, e);
}
diff --git a/gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated14.C
b/gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated14.C
new file mode 100644
index 00000000000..365bca3fd9a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated14.C
@@ -0,0 +1,140 @@
+// PR c++/108243
+// Verify a variable with static storage duration initialized with a
+// constant initializer has constant initialization, and the initializer
+// is manifestly constant-evaluated.
+// { dg-do run { target c++11 } }
+// { dg-additional-options "-fdump-tree-original" }
+
+#include <initializer_list>
+
+struct A {
+ constexpr A(int n) : n(n), m(__builtin_is_constant_evaluated()) { }
+ constexpr A() : A(42) { }
+ void verify_mce() const {
+ if (m != 1) __builtin_abort();
+ }
+ int n;
+ int m;
+};
+
+A a1 = {42};
+A a2{42};
+A a3(42);
+A a4;
+A a5{};
+
+void f() {
+ static A a1 = {42};
+ static A a2{42};
+ static A a3(42);
+ static A a4;
+ static A a5{};
+ for (auto& a : {a1, a2, a3, a4, a5})
+ a.verify_mce();
+}
+
+template<int... N>
+void g() {
+ static A a1 = {42};
+ static A a2{42};
+ static A a3(42);
+ static A a4;
+ static A a5{};
+ static A a6 = {N...};
+ static A a7{N...};
+ static A a8(N...);
+ for (auto& a : {a1, a2, a3, a4, a5, a6, a7, a8})
+ a.verify_mce();
+}
+
+struct B {
+ static A a1;
+ static A a2;
+ static A a3;
+ static A a4;
+ static A a5;
+ static void verify_mce() {
+ for (auto& a : {a1, a2, a3, a4, a5})
+ a.verify_mce();
+ }
+};
+
+A B::a1 = {42};
+A B::a2{42};
+A B::a3(42);
+A B::a4;
+A B::a5{};
+
+template<int... N>
+struct BT {
+ static A a1;
+ static A a2;
+ static A a3;
+ static A a4;
+ static A a5;
+ static A a6;
+ static A a7;
+ static A a8;
+ static void verify_mce() {
+ for (auto& a : {a1, a2, a3, a4, a5})
+ a.verify_mce();
+ }
+};
+
+template<int... N> A BT<N...>::a1 = {42};
+template<int... N> A BT<N...>::a2{42};
+template<int... N> A BT<N...>::a3(42);
+template<int... N> A BT<N...>::a4;
+template<int... N> A BT<N...>::a5{};
+template<int... N> A BT<N...>::a6 = {N...};
+template<int... N> A BT<N...>::a7{N...};
+template<int... N> A BT<N...>::a8(N...);
+
+#if __cpp_inline_variables
+struct BI {
+ static inline A a1 = {42};
+ static inline A a2{42};
+ static inline A a3;
+ static inline A a4{};
+ static void verify_mce() {
+ for (auto& a : {a1, a2, a3, a4})
+ a.verify_mce();
+ }
+};
+
+template<int... N>
+struct BIT {
+ static inline A a1 = {42};
+ static inline A a2{42};
+ static inline A a3;
+ static inline A a4{};
+ static inline A a5 = {N...};
+ static inline A a6{N...};
+ static void verify_mce() {
+ for (auto& a : {a1, a2, a3, a4, a5, a6})
+ a.verify_mce();
+ }
+};
+#endif
+
+int main() {
+ for (auto& a : {a1, a2, a3, a4, a5})
+ a.verify_mce();
+
+ f();
+ g<42>();
+ g<>();
+
+ B::verify_mce();
+ BT<42>::verify_mce();
+ BT<>::verify_mce();
+
+#if __cpp_inline_variables
+ BI::verify_mce();
+ BIT<42>::verify_mce();
+ BIT<>::verify_mce();
+#endif
+}
+
+// { dg-final { scan-tree-dump-not "static initializers for" "original" } }
+// { dg-final { scan-tree-dump-not "cxa_guard_acquire" "original" } }
--
2.39.2.501.gd9d677b2d8
