Here ever since r10-7313-gb599bf9d6d1e18, reduced_constant_expression_p
in C++11/14 is rejecting the marked sub-aggregate initializer (of type S)
W w = {.D.2445={.s={.D.2387={.m=0}, .b=0}}}
^
ultimately because said initializer has CONSTRUCTOR_NO_CLEARING set, and
so the function proceeds to verify that all fields of S are initialized.
And before C++17 we don't expect to see base class fields (since
next_initializable_field skips over the), so the base class initializer
causes r_c_e_p to return false. The base class initializer comes from
the constructor call S::S(int).
The reason this is caused by r10-7313-gb599bf9d6d1e18 is because in that
commit we began using CONSTRUCTOR_NO_CLEARING to also track whether we're
in middle of activating a union member. This overloaded use of the flag
affects clear_no_implicit_zero, which recurses into sub-aggregate
initializers only if the outer initializer has CONSTRUCTOR_NO_CLEARING
set. After that commit, the outer union initializer above no longer has
the flag set at this point and so clear_no_implicit_zero no longer clears
CONSTRUCTOR_NO_CLEARING for the marked inner initializer.
This patch fixes this by restoring the recursive behavior of
clear_no_implicit_zero for union initializers. Arguably we should
we could improve reduced_constant_expression_p to accept the marked
initializer in C++11/14 even if it has CONSTRUCTOR_NO_CLEARING set, but
adjusting clear_no_implicit_zero seems safer to backport.
Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk/12/11/10?
PR c++/105491
gcc/cp/ChangeLog:
* constexpr.cc (clear_no_implicit_zero): Recurse into a union
initializer even if CONSTRUCTOR_NO_CLEARING is already cleared.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/constexpr-union7.C: New test.
* g++.dg/cpp0x/constexpr-union7a.C: New test.
* g++.dg/cpp2a/constinit17.C: New test.
---
gcc/cp/constexpr.cc | 7 +++++-
gcc/testsuite/g++.dg/cpp0x/constexpr-union7.C | 17 +++++++++++++
.../g++.dg/cpp0x/constexpr-union7a.C | 15 ++++++++++++
gcc/testsuite/g++.dg/cpp2a/constinit17.C | 24 +++++++++++++++++++
4 files changed, 62 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-union7.C
create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-union7a.C
create mode 100644 gcc/testsuite/g++.dg/cpp2a/constinit17.C
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index 9b1e71857fc..75fecbcbcb7 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -1886,7 +1886,12 @@ cxx_eval_internal_function (const constexpr_ctx *ctx,
tree t,
static void
clear_no_implicit_zero (tree ctor)
{
- if (CONSTRUCTOR_NO_CLEARING (ctor))
+ if (CONSTRUCTOR_NO_CLEARING (ctor)
+ /* For a union initializer, the flag could already be cleared but not
+ necessarily yet for its sub-aggregates, since for unions the flag is
+ also used by cxx_eval_store_expression to track whether we're in the
+ middle of activating one of its members. */
+ || TREE_CODE (TREE_TYPE (ctor)) == UNION_TYPE)
{
CONSTRUCTOR_NO_CLEARING (ctor) = false;
for (auto &e: CONSTRUCTOR_ELTS (ctor))
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-union7.C
b/gcc/testsuite/g++.dg/cpp0x/constexpr-union7.C
new file mode 100644
index 00000000000..b3147d9db50
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-union7.C
@@ -0,0 +1,17 @@
+// PR c++/105491
+// { dg-do compile { target c++11 } }
+
+struct V {
+ int m = 0;
+};
+struct S : V {
+ constexpr S(int) : b() { }
+ bool b;
+};
+struct W {
+ constexpr W() : s(0) { }
+ union {
+ S s;
+ };
+};
+constexpr W w;
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-union7a.C
b/gcc/testsuite/g++.dg/cpp0x/constexpr-union7a.C
new file mode 100644
index 00000000000..b676e7d1748
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-union7a.C
@@ -0,0 +1,15 @@
+// PR c++/105491
+// { dg-do compile { target c++11 } }
+
+struct V {
+ int m = 0;
+};
+struct S : V {
+ constexpr S(int) : b() { }
+ bool b;
+};
+union W {
+ constexpr W() : s(0) { }
+ S s;
+};
+constexpr W w;
diff --git a/gcc/testsuite/g++.dg/cpp2a/constinit17.C
b/gcc/testsuite/g++.dg/cpp2a/constinit17.C
new file mode 100644
index 00000000000..6431654ac85
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/constinit17.C
@@ -0,0 +1,24 @@
+// PR c++/105491
+// { dg-do compile { target c++11 } }
+
+class Message {
+ virtual int GetMetadata();
+};
+class ProtobufCFileOptions : Message {
+public:
+ constexpr ProtobufCFileOptions(int);
+ bool no_generate_;
+ bool const_strings_;
+ bool use_oneof_field_name_;
+ bool gen_pack_helpers_;
+ bool gen_init_helpers_;
+};
+constexpr ProtobufCFileOptions::ProtobufCFileOptions(int)
+ : no_generate_(), const_strings_(), use_oneof_field_name_(),
+ gen_pack_helpers_(), gen_init_helpers_() {}
+struct ProtobufCFileOptionsDefaultTypeInternal {
+ constexpr ProtobufCFileOptionsDefaultTypeInternal() : _instance({}) {}
+ union {
+ ProtobufCFileOptions _instance;
+ };
+} __constinit _ProtobufCFileOptions_default_instance_;
--
2.36.0.63.gf5aaf72f1b
