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c++: constexpr ref to array of array [PR102307]

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The problem here is that first check_initializer calls
build_aggr_init_full_exprs, which does overload resolution, but then in the
case of failed constexpr throws away the result and does it again in
build_functional_cast.  But in the first overload resolution,
reshape_init_array_1 decided to reuse the inner CONSTRUCTORs because
tf_error is set, so we know we're committed.  But the second pass gets
confused by the CONSTRUCTORs with non-init-list types.

Fixed by avoiding a second pass: instead, pass the call from build_aggr_init
to build_cplus_new, which will turn it into a TARGET_EXPR.  I don't bother
to change the object argument because it will be replaced later in
simplify_aggr_init_expr.

	PR c++/102307

gcc/cp/ChangeLog:

	* decl.cc (check_initializer): Use build_cplus_new in case of
	constexpr failure.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp1z/constexpr-array2.C: New test.
This commit is contained in:
Jason Merrill 2022-04-26 11:15:04 -04:00
parent f106ef5302
commit a578b17b59
2 changed files with 24 additions and 5 deletions
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17
gcc/cp/decl.cc
View File

@ -7397,12 +7397,19 @@ check_initializer (tree decl, tree init, int flags, vec<tree, va_gc> **cleanups)
/* Declared constexpr or constinit, but no suitable initializer;
massage init appropriately so we can pass it into
store_init_value for the error. */
if (CLASS_TYPE_P (type)
&& (!init || TREE_CODE (init) == TREE_LIST))
tree new_init = NULL_TREE;
if (!processing_template_decl
&& TREE_CODE (init_code) == CALL_EXPR)
new_init = build_cplus_new (type, init_code, tf_none);
else if (CLASS_TYPE_P (type)
&& (!init || TREE_CODE (init) == TREE_LIST))
new_init = build_functional_cast (input_location, type,
init, tf_none);
if (new_init)
{
init = build_functional_cast (input_location, type,
init, tf_none);
if (TREE_CODE (init) == TARGET_EXPR)
init = new_init;
if (TREE_CODE (init) == TARGET_EXPR
&& !(flags & LOOKUP_ONLYCONVERTING))
TARGET_EXPR_DIRECT_INIT_P (init) = true;
}
init_code = NULL_TREE;

12
gcc/testsuite/g++.dg/cpp1z/constexpr-array2.C Normal file
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@ -0,0 +1,12 @@
// PR c++/102307
// { dg-do compile { target c++11 } }
#include <array>
template <unsigned N, unsigned M> struct Matrix {
constexpr Matrix(double const (&arr)[N][M]); // { dg-warning "never defined" }
constexpr Matrix(std::array<std::array<double, M>, N> const &arr);
};
int main() {
constexpr Matrix<2, 3>
mat {{ {1.0, 2.0, 3.0}, {4.0, 5.0, 6.0} }}; // { dg-error "before its definition" }
}