This patch implements the C++20 specifier constinit, as described in
<http://wg21.link/p1143r2>. It makes sure that the compiler requires constant
initialization of a variable (it can only be applied to variables with static
or thread storage duration). Note the variable is *not* const; it is posssible
to modify it even after initialization has taken place.
The main bits are in store_init_value. The c-family/ and parser.c bits
handle parsing this new decl-specifier. decl.c is sprinkled with various
checks, e.g. you can't have a parameter declared "constinit".
It was also needed to add the -Wc++20-compat option to warn when "constinit"
was used as an identifier. Note that I am a bit presumptuous about C++20 here,
perhaps I should be only adding -Wc++2a-compat at this point.
As an extension, I'm also adding the __constinit keyword, so that you can
use this feature in C++17 and lesser, effectively supplanting the clang
require_constant_initialization attribute.
I spent significant time writing the tests (I stol^Wborrowed a couple of
reference-related tests from clang, I'll cop to that).
Here's an example of the new diagnostic. For
int nonconst;
constinit int i = nonconst;
we now issue:
q.C:2:15: error: ‘constinit’ variable ‘i’ does not have a constant initializer
2 | constinit int i = nonconst;
| ^
q.C:2:19: error: the value of ‘nonconst’ is not usable in a constant expression
2 | constinit int i = nonconst;
| ^~~~~~~~
q.C:1:5: note: ‘int nonconst’ is not const
1 | int nonconst;
| ^~~~~~~~
I'm not crazy about the two errors, but I felt that revamping the diagnostics
would be out of scope for this patch.
Bootstrapped/regtested on x86_64-linux, ok for trunk?
2019-08-14 Marek Polacek <pola...@redhat.com>
PR c++/91360 - Implement C++20 P1143R2: constinit.
* c-common.c (c_common_reswords): Add constinit and __constinit.
(keyword_is_decl_specifier): Handle RID_CONSTINIT.
* c-common.h (enum rid): Add RID_CONSTINIT, RID_FIRST_CXX20, and
RID_LAST_CXX20.
(D_CXX20): Define.
* c-cppbuiltin.c (c_cpp_builtins): Define __cpp_constinit.
* c-format.c (cxx_keywords): Add "constinit".
* c.opt (Wc++2a-compat, Wc++20-compat): New options.
* cp-tree.h (DECL_DECLARED_CONSTINIT_P): Define.
(enum cp_decl_spec): Add ds_constinit.
* decl.c (duplicate_decls): Set DECL_DECLARED_CONSTINIT_P.
(check_tag_decl): Give an error for constinit in type declarations.
(check_initializer): Also check DECL_DECLARED_CONSTINIT_P.
(cp_finish_decl): Add checking for a constinit declaration.
(grokdeclarator): Add checking for a declaration with the constinit
specifier. Set DECL_DECLARED_CONSTINIT_P for VAR_Ps.
* lex.c (init_reswords): Handle D_CXX20.
* parser.c (cp_lexer_get_preprocessor_token): Pass a better location
to warning_at. Warn about C++20 keywords.
(cp_keyword_starts_decl_specifier_p): Handle RID_CONSTINIT.
(cp_parser_diagnose_invalid_type_name): Add an inform about constinit.
(cp_parser_decl_specifier_seq): Handle RID_CONSTINIT.
(set_and_check_decl_spec_loc): Add "constinit".
* typeck2.c (store_init_value): If a constinit variable wasn't
initialized using a constant initializer, give an error.
* doc/invoke.texi: Document -Wc++20-compat.
* g++.dg/cpp2a/constinit1.C: New test.
* g++.dg/cpp2a/constinit2.C: New test.
* g++.dg/cpp2a/constinit3.C: New test.
* g++.dg/cpp2a/constinit4.C: New test.
* g++.dg/cpp2a/constinit5.C: New test.
* g++.dg/cpp2a/constinit6.C: New test.
* g++.dg/cpp2a/constinit7.C: New test.
* g++.dg/cpp2a/constinit8.C: New test.
* g++.dg/cpp2a/constinit9.C: New test.
* g++.dg/cpp2a/constinit10.C: New test.
* g++.dg/cpp2a/constinit11.C: New test.
* g++.dg/cpp2a/constinit12.C: New test.
diff --git gcc/c-family/c-common.c gcc/c-family/c-common.c
index 610cb905814..eb0f1ba9993 100644
--- gcc/c-family/c-common.c
+++ gcc/c-family/c-common.c
@@ -326,8 +326,9 @@ static bool nonnull_check_p (tree, unsigned HOST_WIDE_INT);
C --std=c89: D_C99 | D_CXXONLY | D_OBJC | D_CXX_OBJC
C --std=c99: D_CXXONLY | D_OBJC
ObjC is like C except that D_OBJC and D_CXX_OBJC are not set
- C++ --std=c++98: D_CONLY | D_CXX11 | D_OBJC
- C++ --std=c++11: D_CONLY | D_OBJC
+ C++ --std=c++98: D_CONLY | D_CXX11 | D_CXX20 | D_OBJC
+ C++ --std=c++11: D_CONLY | D_CXX20 | D_OBJC
+ C++ --std=c++2a: D_CONLY | D_OBJC
ObjC++ is like C++ except that D_OBJC is not set
If -fno-asm is used, D_ASM is added to the mask. If
@@ -392,6 +393,7 @@ const struct c_common_resword c_common_reswords[] =
{ "__complex__", RID_COMPLEX, 0 },
{ "__const", RID_CONST, 0 },
{ "__const__", RID_CONST, 0 },
+ { "__constinit", RID_CONSTINIT, D_CXXONLY },
{ "__decltype", RID_DECLTYPE, D_CXXONLY },
{ "__direct_bases", RID_DIRECT_BASES, D_CXXONLY },
{ "__extension__", RID_EXTENSION, 0 },
@@ -462,6 +464,7 @@ const struct c_common_resword c_common_reswords[] =
{ "class", RID_CLASS, D_CXX_OBJC | D_CXXWARN },
{ "const", RID_CONST, 0 },
{ "constexpr", RID_CONSTEXPR, D_CXXONLY | D_CXX11 | D_CXXWARN },
+ { "constinit", RID_CONSTINIT, D_CXXONLY | D_CXX20 | D_CXXWARN },
{ "const_cast", RID_CONSTCAST, D_CXXONLY | D_CXXWARN },
{ "continue", RID_CONTINUE, 0 },
{ "decltype", RID_DECLTYPE, D_CXXONLY | D_CXX11 | D_CXXWARN },
@@ -7912,6 +7915,7 @@ keyword_is_decl_specifier (enum rid keyword)
case RID_TYPEDEF:
case RID_FRIEND:
case RID_CONSTEXPR:
+ case RID_CONSTINIT:
return true;
default:
return false;
diff --git gcc/c-family/c-common.h gcc/c-family/c-common.h
index 117d729091a..17bd7b1c7d8 100644
--- gcc/c-family/c-common.h
+++ gcc/c-family/c-common.h
@@ -180,6 +180,9 @@ enum rid
/* C++11 */
RID_CONSTEXPR, RID_DECLTYPE, RID_NOEXCEPT, RID_NULLPTR, RID_STATIC_ASSERT,
+ /* C++20 */
+ RID_CONSTINIT,
+
/* char8_t */
RID_CHAR8,
@@ -250,6 +253,8 @@ enum rid
RID_FIRST_CXX11 = RID_CONSTEXPR,
RID_LAST_CXX11 = RID_STATIC_ASSERT,
+ RID_FIRST_CXX20 = RID_CONSTINIT,
+ RID_LAST_CXX20 = RID_CONSTINIT,
RID_FIRST_AT = RID_AT_ENCODE,
RID_LAST_AT = RID_AT_IMPLEMENTATION,
RID_FIRST_PQ = RID_IN,
@@ -427,6 +432,7 @@ extern machine_mode c_default_pointer_mode;
#define D_CXX_CONCEPTS 0x0400 /* In C++, only with concepts. */
#define D_TRANSMEM 0X0800 /* C++ transactional memory TS. */
#define D_CXX_CHAR8_T 0X1000 /* In C++, only with -fchar8_t. */
+#define D_CXX20 0x2000 /* In C++, C++20 only. */
#define D_CXX_CONCEPTS_FLAGS D_CXXONLY | D_CXX_CONCEPTS
#define D_CXX_CHAR8_T_FLAGS D_CXXONLY | D_CXX_CHAR8_T
diff --git gcc/c-family/c-cppbuiltin.c gcc/c-family/c-cppbuiltin.c
index d389f8ca4a0..a08b5918209 100644
--- gcc/c-family/c-cppbuiltin.c
+++ gcc/c-family/c-cppbuiltin.c
@@ -986,6 +986,7 @@ c_cpp_builtins (cpp_reader *pfile)
{
/* Set feature test macros for C++2a. */
cpp_define (pfile, "__cpp_conditional_explicit=201806");
+ cpp_define (pfile, "__cpp_constinit=201907");
cpp_define (pfile, "__cpp_nontype_template_parameter_class=201806");
cpp_define (pfile, "__cpp_impl_destroying_delete=201806");
}
diff --git gcc/c-family/c-format.c gcc/c-family/c-format.c
index 6b059969e67..91bae3d6096 100644
--- gcc/c-family/c-format.c
+++ gcc/c-family/c-format.c
@@ -2958,6 +2958,7 @@ static const token_t cxx_keywords[] =
NAME ("catch", NULL),
NAME ("constexpr if", NULL),
NAME ("constexpr", NULL),
+ NAME ("constinit", NULL),
NAME ("consteval", NULL),
NAME ("decltype", NULL),
NAME ("nullptr", NULL),
diff --git gcc/c-family/c.opt gcc/c-family/c.opt
index 257cadfa5f1..4c468d0f6c2 100644
--- gcc/c-family/c.opt
+++ gcc/c-family/c.opt
@@ -400,6 +400,13 @@ Wc++17-compat
C++ ObjC++ Var(warn_cxx17_compat) Warning LangEnabledBy(C++ ObjC++,Wall)
Warn about C++ constructs whose meaning differs between ISO C++ 2014 and ISO
C++ 2017.
+Wc++2a-compat
+C++ ObjC++ Warning Alias(Wc++20-compat) Undocumented
+
+Wc++20-compat
+C++ ObjC++ Var(warn_cxx20_compat) Warning LangEnabledBy(C++ ObjC++,Wall)
+Warn about C++ constructs whose meaning differs between ISO C++ 2017 and ISO
C++ 2020.
+
Wcast-function-type
C ObjC C++ ObjC++ Var(warn_cast_function_type) Warning EnabledBy(Wextra)
Warn about casts between incompatible function types.
diff --git gcc/cp/cp-tree.h gcc/cp/cp-tree.h
index bdb7778c04b..4b4070fdb8e 100644
--- gcc/cp/cp-tree.h
+++ gcc/cp/cp-tree.h
@@ -489,6 +489,7 @@ extern GTY(()) tree cp_global_trees[CPTI_MAX];
DECL_MUTABLE_P (in FIELD_DECL)
DECL_DEPENDENT_P (in USING_DECL)
LABEL_DECL_BREAK (in LABEL_DECL)
+ DECL_DECLARED_CONSTINIT_P (in VAR_DECL)
1: C_TYPEDEF_EXPLICITLY_SIGNED (in TYPE_DECL).
DECL_TEMPLATE_INSTANTIATED (in a VAR_DECL or a FUNCTION_DECL)
DECL_MEMBER_TEMPLATE_P (in TEMPLATE_DECL)
@@ -3162,6 +3163,10 @@ struct GTY(()) lang_decl {
#define DECL_DECLARED_CONSTEXPR_P(DECL) \
DECL_LANG_FLAG_8 (VAR_OR_FUNCTION_DECL_CHECK (STRIP_TEMPLATE (DECL)))
+/* True if DECL is declared 'constinit'. */
+#define DECL_DECLARED_CONSTINIT_P(DECL) \
+ DECL_LANG_FLAG_0 (VAR_DECL_CHECK (STRIP_TEMPLATE (DECL)))
+
// True if NODE was declared as 'concept'. The flag implies that the
// declaration is constexpr, that the declaration cannot be specialized or
// refined, and that the result type must be convertible to bool.
@@ -5815,6 +5820,7 @@ enum cp_decl_spec {
ds_alias,
ds_constexpr,
ds_complex,
+ ds_constinit,
ds_thread,
ds_type_spec,
ds_redefined_builtin_type_spec,
diff --git gcc/cp/decl.c gcc/cp/decl.c
index ff3b90dba54..943f338696c 100644
--- gcc/cp/decl.c
+++ gcc/cp/decl.c
@@ -2205,8 +2205,12 @@ duplicate_decls (tree newdecl, tree olddecl, bool
newdecl_is_friend)
DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P (newdecl)
|= DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P (olddecl);
if (DECL_CLASS_SCOPE_P (olddecl))
- DECL_DECLARED_CONSTEXPR_P (newdecl)
- |= DECL_DECLARED_CONSTEXPR_P (olddecl);
+ {
+ DECL_DECLARED_CONSTEXPR_P (newdecl)
+ |= DECL_DECLARED_CONSTEXPR_P (olddecl);
+ DECL_DECLARED_CONSTINIT_P (newdecl)
+ |= DECL_DECLARED_CONSTINIT_P (olddecl);
+ }
/* Merge the threadprivate attribute from OLDDECL into NEWDECL. */
if (DECL_LANG_SPECIFIC (olddecl)
@@ -4963,6 +4967,9 @@ check_tag_decl (cp_decl_specifier_seq *declspecs,
else if (decl_spec_seq_has_spec_p (declspecs, ds_constexpr))
error_at (declspecs->locations[ds_constexpr],
"%<constexpr%> cannot be used for type declarations");
+ else if (decl_spec_seq_has_spec_p (declspecs, ds_constinit))
+ error_at (declspecs->locations[ds_constinit],
+ "%<constinit%> cannot be used for type declarations");
}
if (declspecs->attributes && warn_attributes && declared_type)
@@ -6596,11 +6603,12 @@ check_initializer (tree decl, tree init, int flags,
vec<tree, va_gc> **cleanups)
about aggregate initialization of non-aggregate classes. */
flags |= LOOKUP_ALREADY_DIGESTED;
}
- else if (DECL_DECLARED_CONSTEXPR_P (decl))
+ else if (DECL_DECLARED_CONSTEXPR_P (decl)
+ || DECL_DECLARED_CONSTINIT_P (decl))
{
- /* Declared constexpr, but no suitable initializer; massage
- init appropriately so we can pass it into store_init_value
- for the error. */
+ /* 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))
{
@@ -7254,6 +7262,18 @@ cp_finish_decl (tree decl, tree init, bool
init_const_expr_p,
if (VAR_P (decl))
{
+ duration_kind dk = decl_storage_duration (decl);
+ /* [dcl.constinit]/1 "The constinit specifier shall be applied
+ only to a declaration of a variable with static or thread storage
+ duration." */
+ if (DECL_DECLARED_CONSTINIT_P (decl)
+ && !(dk == dk_thread || dk == dk_static))
+ {
+ error ("%<constinit%> can only be applied to a variable with static "
+ "or thread storage duration");
+ return;
+ }
+
/* If this is a local variable that will need a mangled name,
register it now. We must do this before processing the
initializer for the variable, since the initialization might
@@ -10478,6 +10498,7 @@ grokdeclarator (const cp_declarator *declarator,
bool template_parm_flag = false;
bool typedef_p = decl_spec_seq_has_spec_p (declspecs, ds_typedef);
bool constexpr_p = decl_spec_seq_has_spec_p (declspecs, ds_constexpr);
+ bool constinit_p = decl_spec_seq_has_spec_p (declspecs, ds_constinit);
bool late_return_type_p = false;
bool array_parameter_p = false;
location_t saved_loc = input_location;
@@ -10764,6 +10785,24 @@ grokdeclarator (const cp_declarator *declarator,
return error_mark_node;
}
+ if (constinit_p && typedef_p)
+ {
+ error_at (declspecs->locations[ds_constinit],
+ "%<constinit%> cannot appear in a typedef declaration");
+ return error_mark_node;
+ }
+
+ /* [dcl.spec]/2 "At most one of the constexpr, consteval, and constinit
+ keywords shall appear in a decl-specifier-seq." */
+ if (constinit_p && constexpr_p)
+ {
+ error_at (min_location (declspecs->locations[ds_constinit],
+ declspecs->locations[ds_constexpr]),
+ "can use at most one of the %<constinit%> and %<constexpr%> "
+ "specifiers");
+ return error_mark_node;
+ }
+
/* If there were multiple types specified in the decl-specifier-seq,
issue an error message. */
if (declspecs->multiple_types_p)
@@ -11155,6 +11194,12 @@ grokdeclarator (const cp_declarator *declarator,
"a parameter cannot be declared %<constexpr%>");
constexpr_p = 0;
}
+ else if (constinit_p)
+ {
+ error_at (declspecs->locations[ds_constinit],
+ "a parameter cannot be declared %<constinit%>");
+ constexpr_p = 0;
+ }
}
/* Give error if `virtual' is used outside of class declaration. */
@@ -11595,6 +11640,13 @@ grokdeclarator (const cp_declarator *declarator,
"an array", name);
return error_mark_node;
}
+ if (constinit_p)
+ {
+ error_at (declspecs->locations[ds_constinit],
+ "%<constinit%> on function return type is not "
+ "allowed");
+ return error_mark_node;
+ }
if (ctype == NULL_TREE
&& decl_context == FIELD
@@ -12792,10 +12844,17 @@ grokdeclarator (const cp_declarator *declarator,
else if (constexpr_p)
{
error_at (declspecs->locations[ds_constexpr],
- "non-static data member %qE declared
%<constexpr%>",
- unqualified_id);
+ "non-static data member %qE declared "
+ "%<constexpr%>", unqualified_id);
constexpr_p = false;
}
+ else if (constinit_p)
+ {
+ error_at (declspecs->locations[ds_constinit],
+ "non-static data member %qE declared "
+ "%<constinit%>", unqualified_id);
+ constinit_p = false;
+ }
decl = build_decl (id_loc, FIELD_DECL, unqualified_id, type);
DECL_NONADDRESSABLE_P (decl) = bitfield;
if (bitfield && !unqualified_id)
@@ -13069,6 +13128,9 @@ grokdeclarator (const cp_declarator *declarator,
/* Set constexpr flag on vars (functions got it in grokfndecl). */
if (constexpr_p && VAR_P (decl))
DECL_DECLARED_CONSTEXPR_P (decl) = true;
+ /* And the constinit flag (which only applies to variables). */
+ else if (constinit_p && VAR_P (decl))
+ DECL_DECLARED_CONSTINIT_P (decl) = true;
/* Record constancy and volatility on the DECL itself . There's
no need to do this when processing a template; we'll do this
diff --git gcc/cp/lex.c gcc/cp/lex.c
index 12567da39c4..5b43723a8fa 100644
--- gcc/cp/lex.c
+++ gcc/cp/lex.c
@@ -229,6 +229,8 @@ init_reswords (void)
if (cxx_dialect < cxx11)
mask |= D_CXX11;
+ if (cxx_dialect < cxx2a)
+ mask |= D_CXX20;
if (!flag_concepts)
mask |= D_CXX_CONCEPTS;
if (!flag_tm)
diff --git gcc/cp/parser.c gcc/cp/parser.c
index b56cc6924f4..d5587e2b1fc 100644
--- gcc/cp/parser.c
+++ gcc/cp/parser.c
@@ -834,14 +834,28 @@ cp_lexer_get_preprocessor_token (cp_lexer *lexer,
cp_token *token)
{
/* Warn about the C++0x keyword (but still treat it as
an identifier). */
- warning (OPT_Wc__11_compat,
- "identifier %qE is a keyword in C++11",
- token->u.value);
+ warning_at (token->location, OPT_Wc__11_compat,
+ "identifier %qE is a keyword in C++11",
+ token->u.value);
/* Clear out the C_RID_CODE so we don't warn about this
particular identifier-turned-keyword again. */
C_SET_RID_CODE (token->u.value, RID_MAX);
}
+ if (warn_cxx20_compat
+ && C_RID_CODE (token->u.value) >= RID_FIRST_CXX20
+ && C_RID_CODE (token->u.value) <= RID_LAST_CXX20)
+ {
+ /* Warn about the C++20 keyword (but still treat it as
+ an identifier). */
+ warning_at (token->location, OPT_Wc__20_compat,
+ "identifier %qE is a keyword in C++20",
+ token->u.value);
+
+ /* Clear out the C_RID_CODE so we don't warn about this
+ particular identifier-turned-keyword again. */
+ C_SET_RID_CODE (token->u.value, RID_MAX);
+ }
token->keyword = RID_MAX;
}
@@ -986,6 +1000,7 @@ cp_keyword_starts_decl_specifier_p (enum rid keyword)
case RID_DECLTYPE:
case RID_UNDERLYING_TYPE:
case RID_CONSTEXPR:
+ case RID_CONSTINIT:
return true;
default:
@@ -3355,6 +3370,9 @@ cp_parser_diagnose_invalid_type_name (cp_parser *parser,
tree id,
&& id_equal (id, "thread_local"))
inform (location, "C++11 %<thread_local%> only available with "
"%<-std=c++11%> or %<-std=gnu++11%>");
+ else if (cxx_dialect < cxx2a && id == ridpointers[(int)RID_CONSTINIT])
+ inform (location, "C++20 %<constinit%> only available with "
+ "%<-std=c++2a%> or %<-std=gnu++2a%>");
else if (!flag_concepts && id == ridpointers[(int)RID_CONCEPT])
inform (location, "%<concept%> only available with %<-fconcepts%>");
else if (processing_template_decl && current_class_type
@@ -14001,7 +14019,8 @@ cp_parser_decl_specifier_seq (cp_parser* parser,
{
/* decl-specifier:
friend
- constexpr */
+ constexpr
+ constinit */
case RID_FRIEND:
if (!at_class_scope_p ())
{
@@ -14023,6 +14042,11 @@ cp_parser_decl_specifier_seq (cp_parser* parser,
cp_lexer_consume_token (parser->lexer);
break;
+ case RID_CONSTINIT:
+ ds = ds_constinit;
+ cp_lexer_consume_token (parser->lexer);
+ break;
+
case RID_CONCEPT:
ds = ds_concept;
cp_lexer_consume_token (parser->lexer);
@@ -29510,7 +29534,8 @@ set_and_check_decl_spec_loc (cp_decl_specifier_seq
*decl_specs,
"typedef",
"using",
"constexpr",
- "__complex"
+ "__complex",
+ "constinit"
};
gcc_rich_location richloc (location);
richloc.add_fixit_remove ();
diff --git gcc/cp/typeck2.c gcc/cp/typeck2.c
index 02c3ad5efb0..da51b4232d9 100644
--- gcc/cp/typeck2.c
+++ gcc/cp/typeck2.c
@@ -885,7 +885,22 @@ store_init_value (tree decl, tree init, vec<tree, va_gc>**
cleanups, int flags)
if (!TYPE_REF_P (type))
TREE_CONSTANT (decl) = const_init && decl_maybe_constant_var_p (decl);
if (!const_init)
- value = oldval;
+ {
+ /* [dcl.constinit]/2 "If a variable declared with the constinit
+ specifier has dynamic initialization, the program is
+ ill-formed." */
+ if (DECL_DECLARED_CONSTINIT_P (decl))
+ {
+ error_at (location_of (decl),
+ "%<constinit%> variable %qD does not have a constant "
+ "initializer", decl);
+ if (require_constant_expression (value))
+ cxx_constant_init (value, decl);
+ value = error_mark_node;
+ }
+ else
+ value = oldval;
+ }
}
value = cp_fully_fold_init (value);
diff --git gcc/doc/invoke.texi gcc/doc/invoke.texi
index ca111792885..8782317db96 100644
--- gcc/doc/invoke.texi
+++ gcc/doc/invoke.texi
@@ -295,6 +295,7 @@ Objective-C and Objective-C++ Dialects}.
-Wno-builtin-declaration-mismatch @gol
-Wno-builtin-macro-redefined -Wc90-c99-compat -Wc99-c11-compat @gol
-Wc++-compat -Wc++11-compat -Wc++14-compat -Wc++17-compat @gol
+-Wc++20-compat @gol
-Wcast-align -Wcast-align=strict -Wcast-function-type -Wcast-qual @gol
-Wchar-subscripts -Wcatch-value -Wcatch-value=@var{n} @gol
-Wclobbered -Wcomment -Wconditionally-supported @gol
@@ -6792,6 +6793,12 @@ and ISO C++ 2014. This warning is enabled by
@option{-Wall}.
Warn about C++ constructs whose meaning differs between ISO C++ 2014
and ISO C++ 2017. This warning is enabled by @option{-Wall}.
+@item -Wc++20-compat @r{(C++ and Objective-C++ only)}
+@opindex Wc++20-compat
+@opindex Wno-c++20-compat
+Warn about C++ constructs whose meaning differs between ISO C++ 2017
+and ISO C++ 2020. This warning is enabled by @option{-Wall}.
+
@item -Wcast-qual
@opindex Wcast-qual
@opindex Wno-cast-qual
diff --git gcc/testsuite/g++.dg/cpp2a/constinit1.C
gcc/testsuite/g++.dg/cpp2a/constinit1.C
new file mode 100644
index 00000000000..9d1c0289a62
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp2a/constinit1.C
@@ -0,0 +1,38 @@
+// PR c++/91360 - Implement C++20 P1143R2: constinit
+// { dg-do compile { target c++2a } }
+// Test basic usage of 'constinit'.
+
+const char *g() { return "dynamic init"; }
+constexpr const char *f(bool p) { return p ? "constant init" : g(); } // {
dg-error "call to non-.constexpr. function" }
+
+constinit const char *c = f(true);
+constinit const char *d = f(false); // { dg-error "variable .d. does not have
a constant initializer" }
+// { dg-message "in .constexpr. expansion of" "" { target *-*-* } .-1 }
+static constinit const char *e = f(true);
+
+constexpr int foo(int x) { return x; }
+constinit int i = foo(42);
+constinit int j // { dg-error "variable .j. does not have a constant
initializer" }
+ = foo(i); // { dg-error "not usable in a constant expression" }
+
+int y = 42;
+constinit int x // { dg-error "variable .x. does not have a constant
initializer" }
+ = y; // { dg-error "not usable in a constant expression" }
+
+constinit int z;
+const constinit unsigned cst = 1u;
+
+void
+fn ()
+{
+ static constinit int m = foo(42);
+ static constinit int n // { dg-error "variable .n. does not have a constant
initializer" }
+ = foo(m); // { dg-error "not usable in a constant expression" }
+
+ // Make sure we can still modify constinit variables.
+ c = "foo";
+ i = 10;
+ m = 90;
+ // ... unless they're 'const'.
+ cst *= 2; // { dg-error "assignment of read-only variable" }
+}
diff --git gcc/testsuite/g++.dg/cpp2a/constinit10.C
gcc/testsuite/g++.dg/cpp2a/constinit10.C
new file mode 100644
index 00000000000..a50f285ecb1
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp2a/constinit10.C
@@ -0,0 +1,26 @@
+// PR c++/91360 - Implement C++20 P1143R2: constinit
+// { dg-do compile { target c++2a } }
+// From PR83428.
+
+struct S1
+{
+ constexpr S1 ();
+ int m_i;
+};
+
+struct alignas(64) S2
+{
+ constexpr S2 ()
+ : m_tabS1()
+ {}
+
+ S1 m_tabS1[7];
+};
+
+constinit S2 objX; // { dg-error ".constinit. variable .objX. does not have a
constant initializer" }
+// { dg-error "used before its definition" "" { target *-*-* } .-1 }
+// // { dg-message "in .constexpr. expansion of" "" { target *-*-* } .-2 }
+
+constexpr S1::S1 ()
+: m_i(14)
+{}
diff --git gcc/testsuite/g++.dg/cpp2a/constinit11.C
gcc/testsuite/g++.dg/cpp2a/constinit11.C
new file mode 100644
index 00000000000..acdda73d1cf
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp2a/constinit11.C
@@ -0,0 +1,79 @@
+// PR c++/91360 - Implement C++20 P1143R2: constinit
+// { dg-do compile { target c++2a } }
+
+int foo ();
+constexpr int constfoo () { return 42; }
+int gl = 42;
+
+struct nonliteral {
+ int m;
+ nonliteral() : m() { }
+ nonliteral(int n) : m(n) { }
+ ~nonliteral() {}
+};
+
+struct literal {
+ int m;
+ constexpr literal() : m() { }
+ constexpr literal(int n) : m(n) { }
+};
+
+struct pod {
+ int m;
+};
+
+struct S {
+ static constinit pod p;
+ static constinit pod pc;
+ static const constinit nonliteral n;
+};
+
+struct W {
+ int w = 42;
+};
+
+constinit W w;
+
+constinit const int &r1 = gl;
+constinit thread_local const int &r2 = gl;
+constinit const int &r3 // { dg-error "variable .r3. does not have a constant
initializer" }
+ = foo (); // { dg-error "call to non-.constexpr. function" }
+constinit const literal &r4 = 42;
+constinit const nonliteral &r5 // { dg-error "variable .r5. does not have a
constant initializer" }
+ = 42; // { dg-error "call to non-.constexpr. function" }
+constinit const int &r6 = nonliteral(2).m; // { dg-error "variable .r6. does
not have a constant initializer|call to non-.constexpr. function" }
+
+constinit pod p1;
+constinit pod p2 = { 42 };
+constinit pod p3 = { constfoo() };
+constinit pod p4 = { foo() }; // { dg-error "variable .p4. does not have a
constant initializer|call to non-.constexpr. function" }
+
+constexpr literal lit;
+constinit literal l1 = lit;
+constinit literal l2 = 42;
+constinit literal l3 = constfoo();
+constinit literal l4 = foo(); // { dg-error "variable .l4. does not have a
constant initializer|call to non-.constexpr. function" }
+constinit literal l5 = {};
+constinit literal l6{};
+constinit thread_local literal l7 = lit;
+constinit thread_local literal l8 = 42;
+constinit thread_local literal l9 = constfoo();
+constinit thread_local literal l10 = foo(); // { dg-error "variable .l10. does
not have a constant initializer|call to non-.constexpr. function" }
+constinit thread_local literal l11{};
+
+pod S::p;
+pod S::pc(S::p); // { dg-error "variable .S::pc. does not have a constant
initializer|not usable" }
+
+const nonliteral S::n(42); // { dg-error "variable .S::n. does not have a
constant initializer|call to non-.constexpr. function" }
+constinit int n1 = nonliteral{42}.m; // { dg-error "variable .n1. does not
have a constant initializer|temporary of non-literal type" }
+constinit int n2 = literal{42}.m;
+
+void
+fn1 ()
+{
+ const int c = 42;
+ static constinit const int &l // { dg-error "variable .l. does not have a
constant initializer" }
+ = c; // { dg-error "not a constant" }
+ static const int &l2 = 10;
+ static const int &l3 = gl;
+}
diff --git gcc/testsuite/g++.dg/cpp2a/constinit12.C
gcc/testsuite/g++.dg/cpp2a/constinit12.C
new file mode 100644
index 00000000000..b5b736f87c2
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp2a/constinit12.C
@@ -0,0 +1,14 @@
+// PR c++/91360 - Implement C++20 P1143R2: constinit
+// { dg-do compile { target c++2a } }
+
+struct S {
+ S(int) { }
+};
+
+template <class T>
+struct U {
+ T m;
+ constexpr U(int i) : m(i) { } // { dg-error "call to non-.constexpr.
function" }
+};
+
+constinit U<S> u(42); // { dg-error "does not have a constant
initializer|called in a constant expression" }
diff --git gcc/testsuite/g++.dg/cpp2a/constinit2.C
gcc/testsuite/g++.dg/cpp2a/constinit2.C
new file mode 100644
index 00000000000..3e9f578f8ca
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp2a/constinit2.C
@@ -0,0 +1,14 @@
+// PR c++/91360 - Implement C++20 P1143R2: constinit
+// { dg-do compile { target c++11 } }
+// Test that 'constinit' isn't recognized pre-C++2a, but '__constinit' is.
+
+constinit int g = 42; // { dg-error ".constinit. does not name a type" "" {
target c++17_down } }
+__constinit int g2 = 42;
+static __constinit int g3 = 42;
+
+void
+fn ()
+{
+ static constinit int x = 69; // { dg-error ".constinit. does not name a
type" "" { target c++17_down } }
+ static __constinit int x2 = 69;
+}
diff --git gcc/testsuite/g++.dg/cpp2a/constinit3.C
gcc/testsuite/g++.dg/cpp2a/constinit3.C
new file mode 100644
index 00000000000..316937e5bf3
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp2a/constinit3.C
@@ -0,0 +1,58 @@
+// PR c++/91360 - Implement C++20 P1143R2: constinit
+// { dg-do compile { target c++2a } }
+
+constinit constinit int v1; // { dg-error "duplicate .constinit." }
+constexpr constinit int v2 = 1; // { dg-error "can use at most one of the
.constinit. and .constexpr. specifiers" }
+constinit constexpr int v3 = 1; // { dg-error "an use at most one of the
.constinit. and .constexpr. specifiers" }
+
+extern static constinit int v4; // { dg-error "conflicting specifiers" }
+extern thread_local constinit int v5;
+extern constinit int v6;
+
+constinit typedef int T; // { dg-error ".constinit. cannot appear in a typedef
declaration" }
+
+struct S2 {
+ constinit int m1; // { dg-error "non-static data member .m1. declared
.constinit." }
+ constinit unsigned int b : 32; // { dg-error " non-static data member .b.
declared .constinit." }
+};
+
+struct S3 {
+ constinit S3() {} // { dg-error ".constinit. on function return type is not
allowed" }
+ constinit ~S3() {} // { dg-error ".constinit. on function return type is not
allowed" }
+};
+
+constinit struct S4 { // { dg-error ".constinit. cannot be used for type
declarations" }
+};
+
+template<constinit int I> // { dg-error "a parameter cannot be declared
.constinit." }
+struct X { };
+
+int
+fn1 ()
+{
+ // Not static storage
+ constinit int a1 = 42; // { dg-error ".constinit. can only be applied to a
variable with static or thread storage" }
+ constinit int a2 = 42; // { dg-error ".constinit. can only be applied to a
variable with static or thread storage" }
+ extern constinit int e1;
+
+ return 0;
+}
+
+constinit int // { dg-error ".constinit. on function return type is not
allowed" }
+fn3 ()
+{
+}
+
+void
+fn2 (int i, constinit int p) // { dg-error "a parameter cannot be declared
.constinit." }
+{
+ constinit auto l = [i](){ return i; }; // { dg-error ".constinit. can only
be applied to a variable with static or thread storage" }
+}
+
+struct B { int d; };
+
+void
+fn3 (B b)
+{
+ constinit auto [ a ] = b; // { dg-error ".constinit. can only be applied to
a variable with static or thread storage" }
+}
diff --git gcc/testsuite/g++.dg/cpp2a/constinit4.C
gcc/testsuite/g++.dg/cpp2a/constinit4.C
new file mode 100644
index 00000000000..748a7ffa3a9
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp2a/constinit4.C
@@ -0,0 +1,16 @@
+// PR c++/91360 - Implement C++20 P1143R2: constinit
+// { dg-do compile { target c++2a } }
+
+struct S { };
+constinit extern S s;
+constinit S s2 = { };
+
+struct T {
+ int i;
+};
+
+constinit T t;
+struct U : T {
+ int j;
+};
+constinit U u;
diff --git gcc/testsuite/g++.dg/cpp2a/constinit5.C
gcc/testsuite/g++.dg/cpp2a/constinit5.C
new file mode 100644
index 00000000000..9832a561bf8
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp2a/constinit5.C
@@ -0,0 +1,27 @@
+// PR c++/91360 - Implement C++20 P1143R2: constinit
+// { dg-do compile { target c++2a } }
+// Check that we preserve DECL_DECLARED_CONSTINIT_P in duplicate_decls.
+
+int gl = 42;
+
+struct S {
+ constinit static int m;
+ constinit static int n;
+ constinit static const int &r1;
+ constinit static const int &r2;
+};
+
+int S::m = 42;
+int nonconst;
+int S::n = nonconst; // { dg-error "variable .S::n. does not have a constant
initializer" }
+// { dg-error "not usable in a constant expression" "" { target *-*-* } .-1 }
+
+const int &S::r1 = gl;
+const int &S::r2 = 42;
+
+struct T {
+ constinit static thread_local const int &r1;
+ constinit static thread_local const int &r2;
+};
+thread_local const int &T::r1 = gl;
+thread_local const int &T::r2 = 42; // { dg-error "variable .T::r2. does not
have a constant initializer|not a constant expression" }
diff --git gcc/testsuite/g++.dg/cpp2a/constinit6.C
gcc/testsuite/g++.dg/cpp2a/constinit6.C
new file mode 100644
index 00000000000..73e78832844
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp2a/constinit6.C
@@ -0,0 +1,5 @@
+// PR c++/91360 - Implement C++20 P1143R2: constinit
+// { dg-do compile { target c++17_down } }
+// { dg-options "-Wc++20-compat" }
+
+int constinit; // { dg-warning "identifier .constinit. is a keyword" }
diff --git gcc/testsuite/g++.dg/cpp2a/constinit7.C
gcc/testsuite/g++.dg/cpp2a/constinit7.C
new file mode 100644
index 00000000000..e9a0da3f8c8
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp2a/constinit7.C
@@ -0,0 +1,11 @@
+// PR c++/91360 - Implement C++20 P1143R2: constinit
+// { dg-do compile { target c++11 } }
+
+struct T {
+ constexpr T(int) {}
+ ~T();
+};
+__constinit T x = { 42 };
+// ??? This should be rejected in C++14: copy initialization is not a constant
+// expression on a non-literal type in C++14. But 'constinit' is C++20 only.
+__constinit T y = 42;
diff --git gcc/testsuite/g++.dg/cpp2a/constinit8.C
gcc/testsuite/g++.dg/cpp2a/constinit8.C
new file mode 100644
index 00000000000..c6b2975350c
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp2a/constinit8.C
@@ -0,0 +1,18 @@
+// PR c++/91360 - Implement C++20 P1143R2: constinit
+// { dg-do compile { target c++2a } }
+// Variable templates.
+
+int nonconst;
+
+template<typename T>
+constinit T v1 = 42;
+
+template<typename T>
+constinit T v2 = nonconst; // { dg-error "does not have a constant
initializer|not usable" }
+
+void
+fn ()
+{
+ v1<int>;
+ v2<int>;
+}
diff --git gcc/testsuite/g++.dg/cpp2a/constinit9.C
gcc/testsuite/g++.dg/cpp2a/constinit9.C
new file mode 100644
index 00000000000..4c7f8925169
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp2a/constinit9.C
@@ -0,0 +1,24 @@
+// PR c++/91360 - Implement C++20 P1143R2: constinit
+// { dg-do run { target c++2a } }
+// A run-time test.
+
+constexpr int foo (int x) { return x; }
+constinit int b = foo(42);
+
+int
+main ()
+{
+ if (b != 42)
+ __builtin_abort ();
+ // We can still modify 'b'.
+ b = 10;
+ if (b != 10)
+ __builtin_abort ();
+
+ constinit static int s = foo(14);
+ if (s != 14)
+ __builtin_abort ();
+ s++;
+ if (s != 15)
+ __builtin_abort ();
+}
