https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91353
--- Comment #6 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Current patch (modulo testsuite changes) that seems to work pretty well:
diff --git gcc/c-family/c-cppbuiltin.c gcc/c-family/c-cppbuiltin.c
index 76d1e4a380e..9766d7f96c4 100644
--- gcc/c-family/c-cppbuiltin.c
+++ gcc/c-family/c-cppbuiltin.c
@@ -972,7 +972,8 @@ c_cpp_builtins (cpp_reader *pfile)
cpp_define (pfile, "__cpp_fold_expressions=201603L");
cpp_define (pfile, "__cpp_nontype_template_args=201411L");
cpp_define (pfile, "__cpp_range_based_for=201603L");
- cpp_define (pfile, "__cpp_constexpr=201603L");
+ if (cxx_dialect <= cxx17)
+ cpp_define (pfile, "__cpp_constexpr=201603L");
cpp_define (pfile, "__cpp_if_constexpr=201606L");
cpp_define (pfile, "__cpp_capture_star_this=201603L");
cpp_define (pfile, "__cpp_inline_variables=201606L");
@@ -991,6 +992,7 @@ c_cpp_builtins (cpp_reader *pfile)
{
/* Set feature test macros for C++2a. */
cpp_define (pfile, "__cpp_conditional_explicit=201806L");
+ cpp_define (pfile, "__cpp_constexpr=201907L");
cpp_define (pfile, "__cpp_constinit=201907L");
cpp_define (pfile, "__cpp_nontype_template_parameter_class=201806L");
cpp_define (pfile, "__cpp_impl_destroying_delete=201806L");
diff --git gcc/cp/constexpr.c gcc/cp/constexpr.c
index 8c79b0484fc..5bfbc1f7ce5 100644
--- gcc/cp/constexpr.c
+++ gcc/cp/constexpr.c
@@ -765,7 +765,7 @@ massage_constexpr_body (tree fun, tree body)
bases/fields are uninitialized, and complain if COMPLAIN. */
static bool
-cx_check_missing_mem_inits (tree ctype, tree body, bool complain)
+cx_check_missing_mem_inits (tree ctype, tree body, bool complain, bool
allow_missing = true)
{
unsigned nelts = 0;
@@ -815,13 +815,15 @@ cx_check_missing_mem_inits (tree ctype, tree body, bool
complain)
continue;
if (ANON_AGGR_TYPE_P (TREE_TYPE (field)))
{
- /* Recurse to check the anonummous aggregate member. */
+ /* Recurse to check the anonymous aggregate member. */
bad |= cx_check_missing_mem_inits
- (TREE_TYPE (field), NULL_TREE, complain);
+ (TREE_TYPE (field), NULL_TREE, complain, allow_missing);
if (bad && !complain)
return true;
continue;
}
+ if (cxx_dialect >= cxx2a && allow_missing)
+ continue;
ftype = strip_array_types (TREE_TYPE (field));
if (type_has_constexpr_default_constructor (ftype))
{
@@ -829,6 +831,10 @@ cx_check_missing_mem_inits (tree ctype, tree body, bool
complain)
A constexpr ctor that isn't trivial should have been
added in by now. */
gcc_checking_assert (!TYPE_HAS_COMPLEX_DFLT (ftype)
+ /* If we're only checking for missing
+ inits, non-trivial ctors have not been
+ added yet. */
+ || (cxx_dialect >= cxx2a && !allow_missing)
|| errorcount != 0);
continue;
}
@@ -847,7 +853,7 @@ cx_check_missing_mem_inits (tree ctype, tree body, bool
complain)
{
/* Check the anonymous aggregate initializer is valid. */
bad |= cx_check_missing_mem_inits
- (TREE_TYPE (index), CONSTRUCTOR_ELT (body, i)->value, complain);
+ (TREE_TYPE (index), CONSTRUCTOR_ELT (body, i)->value, complain,
allow_missing);
if (bad && !complain)
return true;
}
@@ -2150,8 +2156,18 @@ cxx_eval_call_expression (const constexpr_ctx *ctx, tree
t,
}
/* The result of a constexpr function must be completely initialized. */
+ // XXX not in C++20 constructor
+ // XXX pedwarn somewhere
if (TREE_CODE (result) == CONSTRUCTOR)
- clear_no_implicit_zero (result);
+ {
+ clear_no_implicit_zero (result);
+ if (cxx_dialect >= cxx2a
+ && DECL_CONSTRUCTOR_P (fun)
+ && DECL_DECLARED_CONSTEXPR_P (fun)
+ && NON_UNION_CLASS_TYPE_P (TREE_TYPE (result))
+ && cx_check_missing_mem_inits (TREE_TYPE (result), result, false,
false))
+ CONSTRUCTOR_NO_CLEARING (result) = true;
+ }
pop_cx_call_context ();
return result;
@@ -2903,8 +2919,7 @@ cxx_eval_array_reference (const constexpr_ctx *ctx, tree
t,
/* Not found. */
- if (TREE_CODE (ary) == CONSTRUCTOR
- && CONSTRUCTOR_NO_CLEARING (ary))
+ if (TREE_CODE (ary) == CONSTRUCTOR && CONSTRUCTOR_NO_CLEARING (ary))
{
/* 'ary' is part of the aggregate initializer we're currently
building; if there's no initializer for this element yet,
diff --git gcc/cp/decl.c gcc/cp/decl.c
index 86e38f4af69..ab6da6080a5 100644
--- gcc/cp/decl.c
+++ gcc/cp/decl.c
@@ -5835,8 +5835,12 @@ check_for_uninitialized_const_var (tree decl, bool
constexpr_context_p,
7.1.6 */
if (VAR_P (decl)
&& !TYPE_REF_P (type)
- && (constexpr_context_p
- || CP_TYPE_CONST_P (type) || var_in_constexpr_fn (decl))
+ && (CP_TYPE_CONST_P (type)
+ /* C++20 permits trivial default initialization in constexpr
+ context (P1331R2). */
+ || (cxx_dialect < cxx2a
+ && (constexpr_context_p
+ || var_in_constexpr_fn (decl))))
&& !DECL_NONTRIVIALLY_INITIALIZED_P (decl))
{
tree field = default_init_uninitialized_part (type);
@@ -5845,7 +5849,7 @@ check_for_uninitialized_const_var (tree decl, bool
constexpr_context_p,
bool show_notes = true;
- if (!constexpr_context_p)
+ if (!constexpr_context_p || cxx_dialect >= cxx2a)
{
if (CP_TYPE_CONST_P (type))
{
diff --git gcc/cp/method.c gcc/cp/method.c
index acba6c6da8c..f01ea6a9128 100644
--- gcc/cp/method.c
+++ gcc/cp/method.c
@@ -1985,10 +1985,12 @@ walk_field_subobs (tree fields, special_function_kind
sfk, tree fnname,
if (bad && deleted_p)
*deleted_p = true;
- /* For an implicitly-defined default constructor to be constexpr,
- every member must have a user-provided default constructor or
- an explicit initializer. */
- if (constexpr_p && !CLASS_TYPE_P (mem_type)
+ /* Before C++20, for an implicitly-defined default constructor to be
+ constexpr, every member must have a user-provided default
constructor
+ or an explicit initializer. */
+ if (constexpr_p
+ && cxx_dialect < cxx2a
+ && !CLASS_TYPE_P (mem_type)
&& TREE_CODE (DECL_CONTEXT (field)) != UNION_TYPE)
{
*constexpr_p = false;
