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c++: constexpr empty aggr [PR105795]

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In this testcase, leaving ctx->ctor pointing to the enclosing object meant
that evaluating the initializer for the subobject clobbered previous
initializers for the enclosing object.  So do update ctx->ctor, just don't
add it to the enclosing object ctor.

	PR c++/105795

gcc/cp/ChangeLog:

	* constexpr.cc (cxx_eval_bare_aggregate): Always call
	init_subob_ctx.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp1z/constexpr-aggr-base1.C: New test.
This commit is contained in:
Jason Merrill 2022-06-01 16:13:48 -04:00
parent 37e4e7f77d
commit db4243bb68
2 changed files with 29 additions and 5 deletions
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7
gcc/cp/constexpr.cc
View file

@ -4777,12 +4777,9 @@ cxx_eval_bare_aggregate (const constexpr_ctx *ctx, tree t,
tree orig_value = value;
/* Like in cxx_eval_store_expression, omit entries for empty fields. */
bool no_slot = TREE_CODE (type) == RECORD_TYPE && is_empty_field (index);
if (no_slot)
new_ctx = *ctx;
else
init_subob_ctx (ctx, new_ctx, index, value);
init_subob_ctx (ctx, new_ctx, index, value);
int pos_hint = -1;
if (new_ctx.ctor != ctx->ctor)
if (new_ctx.ctor != ctx->ctor && !no_slot)
{
/* If we built a new CONSTRUCTOR, attach it now so that other
initializers can refer to it. */

27
gcc/testsuite/g++.dg/cpp1z/constexpr-aggr-base1.C Normal file
View file

@ -0,0 +1,27 @@
// PR c++/105795
// { dg-do compile { target c++17 } }
struct empty
{};
template <typename T>
struct tuple_holder
{
[[no_unique_address]] T value;
};
struct tuple : tuple_holder<int>, tuple_holder<empty>
{};
constexpr auto make_tuple(int&& i, empty&& e)
{
return tuple{i, e};
}
constexpr int foo()
{
auto tuple = make_tuple(1, empty{});
return static_cast<const tuple_holder<int>&>(tuple).value;
}
static_assert (foo() == 1);