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c++: Add C++23 consteval if support - P1938R3 [PR100974]

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The following patch implements consteval if support.
There is a new IF_STMT_CONSTEVAL_P flag on IF_STMT and IF_COND is
boolean_false_node to match the non-manifestly constant evaluation
behavior, while constexpr evaluation special-cases it.  Perhaps cleaner
would be to set the condition to __builtin_is_constant_evaluated () call
but we need the IF_STMT_CONSTEVAL_P flag anyway and the IL would be larger.

And I'm not changing the libstdc++ side, where perhaps we could change
std::is_constant_evaluated definition for
 #ifdef __cpp_if_consteval
case to if consteval { return true; } else { return false; }
but we need to keep it defined to __builtin_is_constant_evaluated ()
for C++20 or older.

2021-06-11  Jakub Jelinek  <jakub@redhat.com>

	PR c++/100974
gcc/c-family/
	* c-cppbuiltin.c (c_cpp_builtins): Predefine __cpp_if_consteval for
	-std=c++2b for P1938R3 consteval if support.
gcc/cp/
	* cp-tree.h (struct saved_scope): Add consteval_if_p
	member.  Formatting fix for the discarded_stmt comment.
	(in_consteval_if_p, IF_STMT_CONSTEVAL_P): Define.
	* parser.c (cp_parser_lambda_expression): Temporarily disable
	in_consteval_if_p when parsing lambda body.
	(cp_parser_selection_statement): Parse consteval if.
	* decl.c (struct named_label_entry): Add in_consteval_if member.
	(level_for_consteval_if): New function.
	(poplevel_named_label_1, check_previous_goto_1, check_goto): Handle
	consteval if.
	* constexpr.c (cxx_eval_builtin_function_call): Clarify in comment
	why CP_BUILT_IN_IS_CONSTANT_EVALUATED needs to *non_constant_p
	for !ctx->manifestly_const_eval.
	(cxx_eval_conditional_expression): For IF_STMT_CONSTEVAL_P evaluate
	condition as if it was __builtin_is_constant_evaluated call.
	(potential_constant_expression_1): For IF_STMT_CONSTEVAL_P always
	recurse on both branches.
	* cp-gimplify.c (genericize_if_stmt): Genericize IF_STMT_CONSTEVAL_P
	as the else branch.
	* pt.c (tsubst_expr) <case IF_STMT>: Copy IF_STMT_CONSTEVAL_P.
	Temporarily set in_consteval_if_p when recursing on
	IF_STMT_CONSTEVAL_P then branch.
	(tsubst_lambda_expr): Temporarily disable
	in_consteval_if_p when instantiating lambda body.
	* call.c (immediate_invocation_p): Return false when
	in_consteval_if_p.
gcc/testsuite/
	* g++.dg/cpp23/consteval-if1.C: New test.
	* g++.dg/cpp23/consteval-if2.C: New test.
	* g++.dg/cpp23/consteval-if3.C: New test.
	* g++.dg/cpp23/consteval-if4.C: New test.
	* g++.dg/cpp23/consteval-if5.C: New test.
	* g++.dg/cpp23/consteval-if6.C: New test.
	* g++.dg/cpp23/consteval-if7.C: New test.
	* g++.dg/cpp23/consteval-if8.C: New test.
	* g++.dg/cpp23/consteval-if9.C: New test.
	* g++.dg/cpp23/consteval-if10.C: New test.
	* g++.dg/cpp23/feat-cxx2b.C: Add __cpp_if_consteval tests.
This commit is contained in:
Jakub Jelinek 2021-06-11 15:50:34 +02:00
parent 9d20ec9747
commit 117c642664
19 changed files with 650 additions and 10 deletions
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1
gcc/c-family/c-cppbuiltin.c
View file

@ -1029,6 +1029,7 @@ c_cpp_builtins (cpp_reader *pfile)
{
/* Set feature test macros for C++23. */
cpp_define (pfile, "__cpp_size_t_suffix=202011L");
cpp_define (pfile, "__cpp_if_consteval=202106L");
}
if (flag_concepts)
{

1
gcc/cp/call.c
View file

@ -8840,6 +8840,7 @@ immediate_invocation_p (tree fn, int nargs)
|| !DECL_IMMEDIATE_FUNCTION_P (current_function_decl))
&& (current_binding_level->kind != sk_function_parms
|| !current_binding_level->immediate_fn_ctx_p)
&& !in_consteval_if_p
/* As an exception, we defer std::source_location::current ()
invocations until genericization because LWG3396 mandates
special behavior for it. */

36
gcc/cp/constexpr.c
View file

@ -1315,7 +1315,10 @@ cxx_eval_builtin_function_call (const constexpr_ctx *ctx, tree t, tree fun,
}
/* For __builtin_is_constant_evaluated, defer it if not
ctx->manifestly_const_eval, otherwise fold it to true. */
ctx->manifestly_const_eval (as sometimes we try to constant evaluate
without manifestly_const_eval even expressions or parts thereof which
will later be manifestly const_eval evaluated), otherwise fold it to
true. */
if (fndecl_built_in_p (fun, CP_BUILT_IN_IS_CONSTANT_EVALUATED,
BUILT_IN_FRONTEND))
{
@ -3298,6 +3301,22 @@ cxx_eval_conditional_expression (const constexpr_ctx *ctx, tree t,
/*lval*/false,
non_constant_p, overflow_p);
VERIFY_CONSTANT (val);
if (TREE_CODE (t) == IF_STMT && IF_STMT_CONSTEVAL_P (t))
{
/* Evaluate the condition as if it was
if (__builtin_is_constant_evaluated ()), i.e. defer it if not
ctx->manifestly_const_eval (as sometimes we try to constant evaluate
without manifestly_const_eval even expressions or parts thereof which
will later be manifestly const_eval evaluated), otherwise fold it to
true. */
if (ctx->manifestly_const_eval)
val = boolean_true_node;
else
{
*non_constant_p = true;
return t;
}
}
/* Don't VERIFY_CONSTANT the other operands. */
if (integer_zerop (val))
val = TREE_OPERAND (t, 2);
@ -8809,10 +8828,17 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
return false;
if (!processing_template_decl)
tmp = cxx_eval_outermost_constant_expr (tmp, true);
if (integer_zerop (tmp))
return RECUR (TREE_OPERAND (t, 2), want_rval);
else if (TREE_CODE (tmp) == INTEGER_CST)
return RECUR (TREE_OPERAND (t, 1), want_rval);
/* potential_constant_expression* isn't told if it is called for
manifestly_const_eval or not, so for consteval if always
process both branches as if the condition is not a known
constant. */
if (TREE_CODE (t) != IF_STMT || !IF_STMT_CONSTEVAL_P (t))
{
if (integer_zerop (tmp))
return RECUR (TREE_OPERAND (t, 2), want_rval);
else if (TREE_CODE (tmp) == INTEGER_CST)
return RECUR (TREE_OPERAND (t, 1), want_rval);
}
tmp = *jump_target;
for (i = 1; i < 3; ++i)
{

8
gcc/cp/cp-gimplify.c
View file

@ -161,7 +161,13 @@ genericize_if_stmt (tree *stmt_p)
if (!else_)
else_ = build_empty_stmt (locus);
if (integer_nonzerop (cond) && !TREE_SIDE_EFFECTS (else_))
/* consteval if has been verified not to have the then_/else_ blocks
entered by gotos/case labels from elsewhere, and as then_ block
can contain unfolded immediate function calls, we have to discard
the then_ block regardless of whether else_ has side-effects or not. */
if (IF_STMT_CONSTEVAL_P (stmt))
stmt = else_;
else if (integer_nonzerop (cond) && !TREE_SIDE_EFFECTS (else_))
stmt = then_;
else if (integer_zerop (cond) && !TREE_SIDE_EFFECTS (then_))
stmt = else_;

10
gcc/cp/cp-tree.h
View file

@ -478,6 +478,7 @@ extern GTY(()) tree cp_global_trees[CPTI_MAX];
AGGR_INIT_ZERO_FIRST (in AGGR_INIT_EXPR)
CONSTRUCTOR_MUTABLE_POISON (in CONSTRUCTOR)
OVL_HIDDEN_P (in OVERLOAD)
IF_STMT_CONSTEVAL_P (in IF_STMT)
SWITCH_STMT_NO_BREAK_P (in SWITCH_STMT)
LAMBDA_EXPR_CAPTURE_OPTIMIZED (in LAMBDA_EXPR)
IMPLICIT_CONV_EXPR_BRACED_INIT (in IMPLICIT_CONV_EXPR)
@ -1813,9 +1814,12 @@ struct GTY(()) saved_scope {
BOOL_BITFIELD x_processing_explicit_instantiation : 1;
BOOL_BITFIELD need_pop_function_context : 1;
/* Nonzero if we are parsing the discarded statement of a constexpr
if-statement. */
/* Nonzero if we are parsing the discarded statement of a constexpr
if-statement. */
BOOL_BITFIELD discarded_stmt : 1;
/* Nonzero if we are parsing or instantiating the compound-statement
of consteval if statement. */
BOOL_BITFIELD consteval_if_p : 1;
int unevaluated_operand;
int inhibit_evaluation_warnings;
@ -1879,6 +1883,7 @@ extern GTY(()) struct saved_scope *scope_chain;
#define processing_explicit_instantiation scope_chain->x_processing_explicit_instantiation
#define in_discarded_stmt scope_chain->discarded_stmt
#define in_consteval_if_p scope_chain->consteval_if_p
#define current_ref_temp_count scope_chain->ref_temp_count
@ -5211,6 +5216,7 @@ more_aggr_init_expr_args_p (const aggr_init_expr_arg_iterator *iter)
#define ELSE_CLAUSE(NODE) TREE_OPERAND (IF_STMT_CHECK (NODE), 2)
#define IF_SCOPE(NODE) TREE_OPERAND (IF_STMT_CHECK (NODE), 3)
#define IF_STMT_CONSTEXPR_P(NODE) TREE_LANG_FLAG_0 (IF_STMT_CHECK (NODE))
#define IF_STMT_CONSTEVAL_P(NODE) TREE_LANG_FLAG_2 (IF_STMT_CHECK (NODE))
/* Like PACK_EXPANSION_EXTRA_ARGS, for constexpr if. IF_SCOPE is used while
building an IF_STMT; IF_STMT_EXTRA_ARGS is used after it is complete. */

27
gcc/cp/decl.c
View file

@ -222,6 +222,7 @@ struct GTY((for_user)) named_label_entry {
bool in_omp_scope;
bool in_transaction_scope;
bool in_constexpr_if;
bool in_consteval_if;
};
#define named_labels cp_function_chain->x_named_labels
@ -491,6 +492,16 @@ level_for_constexpr_if (cp_binding_level *b)
&& IF_STMT_CONSTEXPR_P (b->this_entity));
}
/* True if B is the level for the condition of a consteval if. */
static bool
level_for_consteval_if (cp_binding_level *b)
{
return (b->kind == sk_cond && b->this_entity
&& TREE_CODE (b->this_entity) == IF_STMT
&& IF_STMT_CONSTEVAL_P (b->this_entity));
}
/* Update data for defined and undefined labels when leaving a scope. */
int
@ -530,6 +541,8 @@ poplevel_named_label_1 (named_label_entry **slot, cp_binding_level *bl)
case sk_block:
if (level_for_constexpr_if (bl->level_chain))
ent->in_constexpr_if = true;
else if (level_for_consteval_if (bl->level_chain))
ent->in_consteval_if = true;
break;
default:
break;
@ -3391,6 +3404,7 @@ check_previous_goto_1 (tree decl, cp_binding_level* level, tree names,
bool complained = false;
int identified = 0;
bool saw_eh = false, saw_omp = false, saw_tm = false, saw_cxif = false;
bool saw_ceif = false;
if (exited_omp)
{
@ -3470,6 +3484,12 @@ check_previous_goto_1 (tree decl, cp_binding_level* level, tree names,
loc = EXPR_LOCATION (b->level_chain->this_entity);
saw_cxif = true;
}
else if (!saw_ceif && level_for_consteval_if (b->level_chain))
{
inf = G_(" enters %<consteval if%> statement");
loc = EXPR_LOCATION (b->level_chain->this_entity);
saw_ceif = true;
}
break;
default:
@ -3551,12 +3571,13 @@ check_goto (tree decl)
unsigned ix;
if (ent->in_try_scope || ent->in_catch_scope || ent->in_transaction_scope
|| ent->in_constexpr_if
|| ent->in_constexpr_if || ent->in_consteval_if
|| ent->in_omp_scope || !vec_safe_is_empty (ent->bad_decls))
{
diagnostic_t diag_kind = DK_PERMERROR;
if (ent->in_try_scope || ent->in_catch_scope || ent->in_constexpr_if
|| ent->in_transaction_scope || ent->in_omp_scope)
|| ent->in_consteval_if || ent->in_transaction_scope
|| ent->in_omp_scope)
diag_kind = DK_ERROR;
complained = identify_goto (decl, DECL_SOURCE_LOCATION (decl),
&input_location, diag_kind);
@ -3602,6 +3623,8 @@ check_goto (tree decl)
inform (input_location, " enters synchronized or atomic statement");
else if (ent->in_constexpr_if)
inform (input_location, " enters %<constexpr if%> statement");
else if (ent->in_consteval_if)
inform (input_location, " enters %<consteval if%> statement");
}
if (ent->in_omp_scope)

102
gcc/cp/parser.c
View file

@ -10902,6 +10902,11 @@ cp_parser_lambda_expression (cp_parser* parser)
bool discarded = in_discarded_stmt;
in_discarded_stmt = 0;
/* Similarly the body of a lambda in immediate function context is not
in immediate function context. */
bool save_in_consteval_if_p = in_consteval_if_p;
in_consteval_if_p = false;
/* By virtue of defining a local class, a lambda expression has access to
the private variables of enclosing classes. */
@ -10932,6 +10937,7 @@ cp_parser_lambda_expression (cp_parser* parser)
finish_struct (type, /*attributes=*/NULL_TREE);
in_consteval_if_p = save_in_consteval_if_p;
in_discarded_stmt = discarded;
parser->num_template_parameter_lists = saved_num_template_parameter_lists;
@ -12324,6 +12330,102 @@ cp_parser_selection_statement (cp_parser* parser, bool *if_p,
"%<if constexpr%> only available with "
"%<-std=c++17%> or %<-std=gnu++17%>");
}
int ce = 0;
if (keyword == RID_IF && !cx)
{
if (cp_lexer_next_token_is_keyword (parser->lexer,
RID_CONSTEVAL))
ce = 1;
else if (cp_lexer_next_token_is (parser->lexer, CPP_NOT)
&& cp_lexer_nth_token_is_keyword (parser->lexer, 2,
RID_CONSTEVAL))
{
ce = -1;
cp_lexer_consume_token (parser->lexer);
}
}
if (ce)
{
cp_token *tok = cp_lexer_consume_token (parser->lexer);
if (cxx_dialect < cxx23)
pedwarn (tok->location, OPT_Wc__23_extensions,
"%<if consteval%> only available with "
"%<-std=c++2b%> or %<-std=gnu++2b%>");
bool save_in_consteval_if_p = in_consteval_if_p;
statement = begin_if_stmt ();
IF_STMT_CONSTEVAL_P (statement) = true;
condition = finish_if_stmt_cond (boolean_false_node, statement);
gcc_rich_location richloc = tok->location;
bool non_compound_stmt_p = false;
if (cp_lexer_next_token_is_not (parser->lexer, CPP_OPEN_BRACE))
{
non_compound_stmt_p = true;
richloc.add_fixit_insert_after (tok->location, "{");
}
in_consteval_if_p |= ce > 0;
cp_parser_implicitly_scoped_statement (parser, NULL, guard_tinfo);
if (non_compound_stmt_p)
{
location_t before_loc
= cp_lexer_peek_token (parser->lexer)->location;
richloc.add_fixit_insert_before (before_loc, "}");
error_at (&richloc,
"%<if consteval%> requires compound statement");
non_compound_stmt_p = false;
}
finish_then_clause (statement);
/* If the next token is `else', parse the else-clause. */
if (cp_lexer_next_token_is_keyword (parser->lexer,
RID_ELSE))
{
cp_token *else_tok = cp_lexer_peek_token (parser->lexer);
gcc_rich_location else_richloc = else_tok->location;
guard_tinfo = get_token_indent_info (else_tok);
/* Consume the `else' keyword. */
cp_lexer_consume_token (parser->lexer);
begin_else_clause (statement);
if (cp_lexer_next_token_is_not (parser->lexer, CPP_OPEN_BRACE))
{
non_compound_stmt_p = true;
else_richloc.add_fixit_insert_after (else_tok->location,
"{");
}
in_consteval_if_p = save_in_consteval_if_p | (ce < 0);
cp_parser_implicitly_scoped_statement (parser, NULL,
guard_tinfo);
if (non_compound_stmt_p)
{
location_t before_loc
= cp_lexer_peek_token (parser->lexer)->location;
else_richloc.add_fixit_insert_before (before_loc, "}");
error_at (&else_richloc,
"%<if consteval%> requires compound statement");
}
finish_else_clause (statement);
}
in_consteval_if_p = save_in_consteval_if_p;
if (ce < 0)
{
std::swap (THEN_CLAUSE (statement), ELSE_CLAUSE (statement));
if (THEN_CLAUSE (statement) == NULL_TREE)
THEN_CLAUSE (statement) = build_empty_stmt (tok->location);
}
finish_if_stmt (statement);
return statement;
}
/* Look for the `('. */
matching_parens parens;

13
gcc/cp/pt.c
View file

@ -18413,6 +18413,7 @@ tsubst_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl,
case IF_STMT:
stmt = begin_if_stmt ();
IF_STMT_CONSTEXPR_P (stmt) = IF_STMT_CONSTEXPR_P (t);
IF_STMT_CONSTEVAL_P (stmt) = IF_STMT_CONSTEVAL_P (t);
if (IF_STMT_CONSTEXPR_P (t))
args = add_extra_args (IF_STMT_EXTRA_ARGS (t), args);
tmp = RECUR (IF_COND (t));
@ -18433,6 +18434,13 @@ tsubst_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl,
}
if (IF_STMT_CONSTEXPR_P (t) && integer_zerop (tmp))
/* Don't instantiate the THEN_CLAUSE. */;
else if (IF_STMT_CONSTEVAL_P (t))
{
bool save_in_consteval_if_p = in_consteval_if_p;
in_consteval_if_p = true;
RECUR (THEN_CLAUSE (t));
in_consteval_if_p = save_in_consteval_if_p;
}
else
{
tree folded = fold_non_dependent_expr (tmp, complain);
@ -19385,6 +19393,9 @@ tsubst_lambda_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl)
local_specialization_stack s (lss_copy);
bool save_in_consteval_if_p = in_consteval_if_p;
in_consteval_if_p = false;
tree body = start_lambda_function (fn, r);
/* Now record them for lookup_init_capture_pack. */
@ -19425,6 +19436,8 @@ tsubst_lambda_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl)
finish_lambda_function (body);
in_consteval_if_p = save_in_consteval_if_p;
if (nested)
pop_function_context ();
else

103
gcc/testsuite/g++.dg/cpp23/consteval-if1.C Normal file
View file

@ -0,0 +1,103 @@
// P1938R3
// { dg-do run { target c++20 } }
// { dg-options "" }
extern "C" void abort ();
namespace std {
constexpr inline bool
is_constant_evaluated () noexcept
{
if consteval { // { dg-warning "'if consteval' only available with" "" { target c++20_only } }
return true;
} else {
return false;
}
}
}
consteval int foo (int x) { return x; }
consteval int bar () { return 2; }
constexpr int
baz (int x)
{
int r = 0;
if consteval // { dg-warning "'if consteval' only available with" "" { target c++20_only } }
{
r += foo (x);
}
else
{
r += bar ();
}
if ! consteval // { dg-warning "'if consteval' only available with" "" { target c++20_only } }
{
r += 2 * bar ();
}
else
{
r += foo (8 * x);
}
if (std::is_constant_evaluated ())
r = -r;
if consteval // { dg-warning "'if consteval' only available with" "" { target c++20_only } }
{
r += foo (32 * x);
}
if not consteval // { dg-warning "'if consteval' only available with" "" { target c++20_only } }
{
r += 32 * bar ();
}
return r;
}
template <typename T>
constexpr int
qux (T x)
{
T r = 0;
if consteval // { dg-warning "'if consteval' only available with" "" { target c++20_only } }
{
r += foo (x);
}
else
{
r += bar ();
}
if ! consteval // { dg-warning "'if consteval' only available with" "" { target c++20_only } }
{
r += 2 * bar ();
}
else
{
r += foo (8 * x);
}
if (std::is_constant_evaluated ())
r = -r;
if consteval // { dg-warning "'if consteval' only available with" "" { target c++20_only } }
{
r += foo (32 * x);
}
if not consteval // { dg-warning "'if consteval' only available with" "" { target c++20_only } }
{
r += 32 * bar ();
}
return r;
}
constexpr int a = baz (1);
static_assert (a == 23);
int b = baz (1);
constexpr int c = qux (1);
static_assert (c == 23);
int d = qux<int> (1);
int
main ()
{
if (b != 23 || d != 23)
abort ();
if (baz (1) != 70 || qux (1) != 70 || qux (1LL) != 70)
abort ();
}

36
gcc/testsuite/g++.dg/cpp23/consteval-if10.C Normal file
View file

@ -0,0 +1,36 @@
// P1938R3
// { dg-do compile { target c++20 } }
// { dg-options "" }
consteval int foo (int x) { return x; }
constexpr int
bar (int x)
{
int r = 0;
if consteval // { dg-warning "'if consteval' only available with" "" { target c++20_only } }
{
auto y = [=] { foo (x); }; // { dg-error "'x' is not a constant expression" }
y ();
}
return r;
}
template <typename T>
constexpr T
baz (T x)
{
T r = 0;
if consteval // { dg-warning "'if consteval' only available with" "" { target c++20_only } }
{
auto y = [=] { foo (x); }; // { dg-error "'x' is not a constant expression" }
y ();
}
return r;
}
int
qux (int x)
{
return baz (x);
}

129
gcc/testsuite/g++.dg/cpp23/consteval-if2.C Normal file
View file

@ -0,0 +1,129 @@
// P1938R3
// { dg-do compile { target c++20 } }
// { dg-options "" }
constexpr bool f()
{
if consteval (true) {} // { dg-error "'if consteval' requires compound statement" }
// { dg-error "expected" "" { target *-*-* } .-1 }
// { dg-warning "'if consteval' only available with" "" { target c++20_only } .-2 }
if not consteval (false) {} // { dg-error "'if consteval' requires compound statement" }
// { dg-error "expected" "" { target *-*-* } .-1 }
// { dg-warning "'if consteval' only available with" "" { target c++20_only } .-2 }
if consteval if (true) {} // { dg-error "'if consteval' requires compound statement" }
// { dg-warning "'if consteval' only available with" "" { target c++20_only } .-1 }
if ! consteval {} else ; // { dg-error "'if consteval' requires compound statement" }
// { dg-warning "'if consteval' only available with" "" { target c++20_only } .-1 }
if consteval {} else if (true) {} // { dg-error "'if consteval' requires compound statement" }
// { dg-warning "'if consteval' only available with" "" { target c++20_only } .-1 }
if (true)
if consteval // { dg-warning "'if consteval' only available with" "" { target c++20_only } }
{
}
else ; // { dg-error "'if consteval' requires compound statement" }
return false;
}
consteval int foo (int x) { return x; }
consteval int bar () { return 2; }
constexpr int
baz (int x)
{
int r = 0;
if not consteval // { dg-warning "'if consteval' only available with" "" { target c++20_only } }
{
r += foo (x); // { dg-error "'x' is not a constant expression" }
}
else
{
r += bar ();
}
if consteval // { dg-warning "'if consteval' only available with" "" { target c++20_only } }
{
r += 2 * bar ();
}
else
{
r += foo (8 * x); // { dg-error "'x' is not a constant expression" }
}
if ! consteval // { dg-warning "'if consteval' only available with" "" { target c++20_only } }
{
r += foo (32 * x);// { dg-error "'x' is not a constant expression" }
}
if consteval // { dg-warning "'if consteval' only available with" "" { target c++20_only } }
{
r += 32 * bar ();
}
return r;
}
template <typename T>
constexpr int
qux (int x)
{
int r = 0;
if not consteval // { dg-warning "'if consteval' only available with" "" { target c++20_only } }
{
r += foo (x); // { dg-error "'x' is not a constant expression" }
}
else
{
r += bar ();
}
if consteval // { dg-warning "'if consteval' only available with" "" { target c++20_only } }
{
r += 2 * bar ();
}
else
{
r += foo (8 * x); // { dg-error "is not a constant expression" }
}
if ! consteval // { dg-warning "'if consteval' only available with" "" { target c++20_only } }
{
r += foo (32 * x);// { dg-error "is not a constant expression" }
}
if consteval // { dg-warning "'if consteval' only available with" "" { target c++20_only } }
{
r += 32 * bar ();
}
return r;
}
template <typename T>
constexpr T
corge (T x)
{
T r = 0;
if not consteval // { dg-warning "'if consteval' only available with" "" { target c++20_only } }
{
r += foo (x); // { dg-error "'x' is not a constant expression" }
}
else
{
r += bar ();
}
if consteval // { dg-warning "'if consteval' only available with" "" { target c++20_only } }
{
r += 2 * bar ();
}
else
{
r += foo (8 * x); // { dg-error "is not a constant expression" }
}
if ! consteval // { dg-warning "'if consteval' only available with" "" { target c++20_only } }
{
r += foo (32 * x);// { dg-error "is not a constant expression" }
}
if consteval // { dg-warning "'if consteval' only available with" "" { target c++20_only } }
{
r += 32 * bar ();
}
return r;
}
int
garply (int x)
{
return corge (x);
}

73
gcc/testsuite/g++.dg/cpp23/consteval-if3.C Normal file
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@ -0,0 +1,73 @@
// P1938R3
// { dg-do run { target c++20 } }
// { dg-options "" }
constexpr inline bool
is_constant_evaluated () noexcept
{
if consteval { return true; } else { return false; } // { dg-warning "'if consteval' only available with" "" { target c++20_only } }
}
template<int N> struct X { int v = N; };
X<is_constant_evaluated ()> x; // type X<true>
int y = 4;
int a = is_constant_evaluated () ? y : 1; // initializes a to 1
int b = is_constant_evaluated () ? 2 : y; // initializes b to 2
int c = y + (is_constant_evaluated () ? 2 : y); // initializes c to 2*y
int d = is_constant_evaluated (); // initializes d to 1
int e = d + is_constant_evaluated (); // initializes e to 1 + 0
struct false_type { static constexpr bool value = false; };
struct true_type { static constexpr bool value = true; };
template<class T, class U>
struct is_same : false_type {};
template<class T>
struct is_same<T, T> : true_type {};
constexpr int
foo (int x)
{
const int n = is_constant_evaluated () ? 13 : 17; // n == 13
int m = is_constant_evaluated () ? 13 : 17; // m might be 13 or 17 (see below)
char arr[n] = {}; // char[13]
return m + sizeof (arr) + x;
}
constexpr int
bar ()
{
const int n = is_constant_evaluated() ? 13 : 17;
X<n> x1;
X<is_constant_evaluated() ? 13 : 17> x2;
static_assert (is_same<decltype (x1), decltype (x2)>::value, "x1/x2's type");
return x1.v + x2.v;
}
int p = foo (0); // m == 13; initialized to 26
int q = p + foo (0); // m == 17 for this call; initialized to 56
static_assert (bar () == 26, "bar");
struct S { int a, b; };
S s = { is_constant_evaluated () ? 2 : 3, y };
S t = { is_constant_evaluated () ? 2 : 3, 4 };
static_assert (is_same<decltype (x), X<true> >::value, "x's type");
int
main ()
{
if (a != 1 || b != 2 || c != 8 || d != 1 || e != 1 || p != 26 || q != 56)
__builtin_abort ();
if (s.a != 3 || s.b != 4 || t.a != 2 || t.b != 4)
__builtin_abort ();
if (foo (y) != 34)
__builtin_abort ();
#if __cplusplus >= 201703L
if constexpr (foo (0) != 26)
__builtin_abort ();
#endif
constexpr int w = foo (0);
if (w != 26)
__builtin_abort ();
}

44
gcc/testsuite/g++.dg/cpp23/consteval-if4.C Normal file
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@ -0,0 +1,44 @@
// { dg-do compile { target c++20 } }
// { dg-options "-w" }
void f()
{
goto l; // { dg-message "from here" }
if consteval // { dg-message "enters 'consteval if'" }
{
l:; // { dg-error "jump to label" }
}
}
void g()
{
goto l; // { dg-message "from here" }
if not consteval // { dg-message "enters 'consteval if'" }
{
l:; // { dg-error "jump to label" }
}
}
void h()
{
goto l; // { dg-message "from here" }
if consteval // { dg-message "enters 'consteval if'" }
{
}
else
{
l:; // { dg-error "jump to label" }
}
}
void i()
{
goto l; // { dg-message "from here" }
if not consteval // { dg-message "enters 'consteval if'" }
{
}
else
{
l:; // { dg-error "jump to label" }
}
}

14
gcc/testsuite/g++.dg/cpp23/consteval-if5.C Normal file
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@ -0,0 +1,14 @@
// { dg-do compile { target c++20 } }
// { dg-options "-w" }
void f()
{
if consteval // { dg-message "enters 'consteval if'" }
{
goto l; // { dg-message "from here" }
}
else
{
l:; // { dg-error "jump to label" }
}
}

16
gcc/testsuite/g++.dg/cpp23/consteval-if6.C Normal file
View file

@ -0,0 +1,16 @@
// { dg-do compile { target c++20 } }
// { dg-options "-w" }
void f()
{
if consteval
{
goto l;
l:;
}
else
{
goto l2;
l2:;
}
}

16
gcc/testsuite/g++.dg/cpp23/consteval-if7.C Normal file
View file

@ -0,0 +1,16 @@
// { dg-do compile { target c++20 } }
// { dg-options "-w" }
void f()
{
if not consteval
{
l:;
goto l;
}
else
{
l2:;
goto l2;
}
}

14
gcc/testsuite/g++.dg/cpp23/consteval-if8.C Normal file
View file

@ -0,0 +1,14 @@
// { dg-do compile { target c++20 } }
// { dg-options "-w" }
void f()
{
if consteval
{
l:; // { dg-error "jump to label" }
}
else
{
goto l; // { dg-message "from here" }
}
}

11
gcc/testsuite/g++.dg/cpp23/consteval-if9.C Normal file
View file

@ -0,0 +1,11 @@
// { dg-do compile { target c++20 } }
// { dg-options "-w" }
constexpr void f(int i)
{
switch (i)
if consteval // { dg-message "enters 'consteval if'" }
{
case 42:; // { dg-error "jump to case label" }
}
}

6
gcc/testsuite/g++.dg/cpp23/feat-cxx2b.C
View file

@ -545,3 +545,9 @@
#elif __cpp_size_t_suffix != 202011
# error "__cpp_size_t_suffix != 202011"
#endif
#ifndef __cpp_if_consteval
# error "__cpp_if_consteval"
#elif __cpp_if_consteval != 202106
# error "__cpp_if_consteval != 202106"
#endif