From 08f4496aa619f9b0e8dbb459452dd96edb870236 Mon Sep 17 00:00:00 2001
From: Marek Polacek <polacek@redhat.com>
Date: Thu, 25 May 2023 18:54:18 -0400
Subject: [PATCH] c++: wrong error with static constexpr var in tmpl [PR109876]
Since r8-509, we'll no longer create a static temporary var for
the initializer '{ 1, 2 }' for num in the attached test because
the code in finish_compound_literal is now guarded by
'&& fcl_context == fcl_c99' but it's fcl_functional here. This
causes us to reject num as non-constant when evaluating it in
a template.
Jason's idea was to treat num as value-dependent even though it
actually isn't. This patch implements that suggestion.
We weren't marking objects whose type is an empty class type
constant. This patch changes that so that v_d_e_p doesn't need
to check is_really_empty_class.
Co-authored-by: Jason Merrill <jason@redhat.com>
PR c++/109876
gcc/cp/ChangeLog:
* decl.cc (cp_finish_decl): Set TREE_CONSTANT when initializing
an object of empty class type.
* pt.cc (value_dependent_expression_p) <case VAR_DECL>: Treat a
constexpr-declared non-constant variable as value-dependent.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/constexpr-template12.C: New test.
* g++.dg/cpp1z/constexpr-template1.C: New test.
* g++.dg/cpp1z/constexpr-template2.C: New test.
(cherry picked from commit b5138df96a93d3b5070c88b8617eabd38cb24ab6)
---
gcc/cp/decl.cc | 13 +++++--
gcc/cp/pt.cc | 7 ++++
.../g++.dg/cpp0x/constexpr-template12.C | 38 +++++++++++++++++++
.../g++.dg/cpp1z/constexpr-template1.C | 25 ++++++++++++
.../g++.dg/cpp1z/constexpr-template2.C | 25 ++++++++++++
5 files changed, 105 insertions(+), 3 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-template12.C
create mode 100644 gcc/testsuite/g++.dg/cpp1z/constexpr-template1.C
create mode 100644 gcc/testsuite/g++.dg/cpp1z/constexpr-template2.C
diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 30d89bba9e86..bb4f2fb82080 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -8216,7 +8216,6 @@ void
cp_finish_decl (tree decl, tree init, bool init_const_expr_p,
tree asmspec_tree, int flags)
{
- tree type;
vec<tree, va_gc> *cleanups = NULL;
const char *asmspec = NULL;
int was_readonly = 0;
@@ -8236,7 +8235,7 @@ cp_finish_decl (tree decl, tree init, bool init_const_expr_p,
/* Parameters are handled by store_parm_decls, not cp_finish_decl. */
gcc_assert (TREE_CODE (decl) != PARM_DECL);
- type = TREE_TYPE (decl);
+ tree type = TREE_TYPE (decl);
if (type == error_mark_node)
return;
@@ -8426,7 +8425,7 @@ cp_finish_decl (tree decl, tree init, bool init_const_expr_p,
if (decl_maybe_constant_var_p (decl)
/* FIXME setting TREE_CONSTANT on refs breaks the back end. */
&& !TYPE_REF_P (type))
- TREE_CONSTANT (decl) = 1;
+ TREE_CONSTANT (decl) = true;
}
/* This is handled mostly by gimplify.cc, but we have to deal with
not warning about int x = x; as it is a GCC extension to turn off
@@ -8437,6 +8436,14 @@ cp_finish_decl (tree decl, tree init, bool init_const_expr_p,
&& !warning_enabled_at (DECL_SOURCE_LOCATION (decl), OPT_Winit_self))
suppress_warning (decl, OPT_Winit_self);
}
+ else if (VAR_P (decl)
+ && COMPLETE_TYPE_P (type)
+ && !TYPE_REF_P (type)
+ && !dependent_type_p (type)
+ && is_really_empty_class (type, /*ignore_vptr*/false))
+ /* We have no initializer but there's nothing to initialize anyway.
+ Treat DECL as constant due to c++/109876. */
+ TREE_CONSTANT (decl) = true;
if (flag_openmp
&& TREE_CODE (decl) == FUNCTION_DECL
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 761df45f2749..f056a4f38e64 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -27989,6 +27989,13 @@ value_dependent_expression_p (tree expression)
&& value_expr == error_mark_node))
return true;
}
+ /* We have a constexpr variable and we're processing a template. When
+ there's lifetime extension involved (for which finish_compound_literal
+ used to create a temporary), we'll not be able to evaluate the
+ variable until instantiating, so pretend it's value-dependent. */
+ else if (DECL_DECLARED_CONSTEXPR_P (expression)
+ && !TREE_CONSTANT (expression))
+ return true;
return false;
case DYNAMIC_CAST_EXPR:
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-template12.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-template12.C
new file mode 100644
index 000000000000..a9e065320c85
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-template12.C
@@ -0,0 +1,38 @@
+// PR c++/109876
+// { dg-do compile { target c++11 } }
+
+using size_t = decltype(sizeof 0);
+
+namespace std {
+template <class> struct initializer_list {
+ const int *_M_array;
+ size_t _M_len;
+ constexpr size_t size() const { return _M_len; }
+};
+} // namespace std
+
+constexpr std::initializer_list<int> gnum{2};
+
+template <int> struct Array {};
+template <int> void g()
+{
+ static constexpr std::initializer_list<int> num{2};
+ static_assert(num.size(), "");
+ Array<num.size()> ctx;
+
+ constexpr Array<1> num1{};
+}
+
+template <int N>
+struct Foo
+{
+ static constexpr std::initializer_list<int> num = { 1, 2 };
+ static_assert(num.size(), "");
+ Array<num.size()> ctx;
+};
+
+void
+f (Foo<5>)
+{
+ g<0>();
+}
diff --git a/gcc/testsuite/g++.dg/cpp1z/constexpr-template1.C b/gcc/testsuite/g++.dg/cpp1z/constexpr-template1.C
new file mode 100644
index 000000000000..58be046fd367
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/constexpr-template1.C
@@ -0,0 +1,25 @@
+// PR c++/109876
+// { dg-do compile { target c++17 } }
+
+struct Foo {};
+template <const Foo&> struct X {};
+
+void g()
+{
+ static constexpr Foo foo;
+ X<foo> x;
+}
+
+template<int>
+void f()
+{
+ static constexpr Foo foo;
+ X<foo> x;
+}
+
+void
+h ()
+{
+ f<0>();
+ f<1>();
+}
diff --git a/gcc/testsuite/g++.dg/cpp1z/constexpr-template2.C b/gcc/testsuite/g++.dg/cpp1z/constexpr-template2.C
new file mode 100644
index 000000000000..5a9a96ba60ad
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/constexpr-template2.C
@@ -0,0 +1,25 @@
+// PR c++/109876
+// { dg-do compile { target c++17 } }
+
+struct Foo {};
+template <const Foo&> struct X {};
+
+void g()
+{
+ static constexpr Foo foo{};
+ X<foo> x;
+}
+
+template<int>
+void f()
+{
+ static constexpr Foo foo{};
+ X<foo> x;
+}
+
+void
+h ()
+{
+ f<0>();
+ f<1>();
+}
--
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