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c++: Don't substitute into constraints on lambdas [PR99874]

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We currently substitute through a lambda's constraints whenever we
regenerate it via tsubst_lambda_expr.  This is the wrong approach
because it can lead to hard errors due to constraints being evaluated
out of order (as in the testcase concepts-lambda17.C below), and because
it doesn't mesh well with the recently added REQUIRES_EXPR_EXTRA_ARGS
mechanism for delaying substitution into requires-expressions, which is
the cause of this PR.

But in order to avoid substituting through a lambda's constraints during
regeneration, we need to be able to get at all in-scope template
parameters and corresponding template arguments during constraint
checking of a lambda's op().  And this information is not easily
available when we need it, it seems.

To that end, the approach that this patch takes is to add two new fields
to LAMBDA_EXPR (and remove one): LAMBDA_EXPR_REGENERATED_FROM
(replacing LAMBDA_EXPR_INSTANTIATED), and LAMBDA_EXPR_REGENERATING_TARGS.
The former allows us to obtain the complete set of template parameters
that are in-scope for a lambda's op(), and the latter gives us all outer
template arguments that were used to regenerate the lambda (analogous to
the TI_TEMPLATE and TI_ARGS of a TEMPLATE_INFO, respectively).

LAMBDA_EXPR_REGENERATING_TARGS is not strictly necessary -- in an
earlier prototype, I walked LAMBDA_EXPR_EXTRA_SCOPE to build up this set
of outer template arguments on demand, but it seems cleaner to do it this
way.  (We'd need to walk LAMBDA_EXPR_EXTRA_SCOPE and not DECL/TYPE_CONTEXT
because the latter skips over variable template scopes.)

This patch also renames the predicate instantiated_lambda_fn_p to
regenerated_lambda_fn_p, for sake of consistency with the rest of the
patch which uses "regenerated" instead of "instantiated".

gcc/cp/ChangeLog:

	PR c++/99874
	* constraint.cc (get_normalized_constraints_from_decl): Handle
	regenerated lambdas.
	(satisfy_declaration_constraints): Likewise.  Check for
	dependent args later.
	* cp-tree.h (LAMBDA_EXPR_INSTANTIATED): Replace with ...
	(LAMBDA_EXPR_REGENERATED_FROM): ... this.
	(LAMBDA_EXPR_REGENERATING_TARGS): New.
	(tree_lambda_expr::regenerated_from): New data member.
	(tree_lambda_expr::regenerating_targs): New data member.
	(add_to_template_args): Declare.
	(regenerated_lambda_fn_p): Likewise.
	(most_general_lambda): Likewise.
	* lambda.c (build_lambda_expr): Set LAMBDA_EXPR_REGENERATED_FROM
	and LAMBDA_EXPR_REGENERATING_TARGS.
	* pt.c (add_to_template_args): No longer static.
	(tsubst_function_decl): Unconditionally propagate constraints on
	the substituted function decl.
	(instantiated_lambda_fn_p): Rename to ...
	(regenerated_lambda_fn_p): ... this.  Check
	LAMBDA_EXPR_REGENERATED_FROM instead of
	LAMBDA_EXPR_INSTANTIATED.
	(most_general_lambda): Define.
	(enclosing_instantiation_of): Adjust after renaming
	instantiated_lambda_fn_p.
	(tsubst_lambda_expr): Don't set LAMBDA_EXPR_INSTANTIATED.  Set
	LAMBDA_EXPR_REGENERATED_FROM and LAMBDA_EXPR_REGENERATING_TARGS.
	Don't substitute or set constraints on the regenerated lambda.

gcc/testsuite/ChangeLog:

	PR c++/99874
	* g++.dg/cpp2a/concepts-lambda16.C: New test.
	* g++.dg/cpp2a/concepts-lambda17.C: New test.
This commit is contained in:
Patrick Palka 2021-04-08 13:07:43 -04:00
parent 05708d6eef
commit 123b3e03c9
6 changed files with 151 additions and 33 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

35
gcc/cp/constraint.cc
View File

@ -886,6 +886,16 @@ get_normalized_constraints_from_decl (tree d, bool diag = false)
it has the correct template information attached. */
d = strip_inheriting_ctors (d);
if (regenerated_lambda_fn_p (d))
{
/* If this lambda was regenerated, DECL_TEMPLATE_PARMS doesn't contain
all in-scope template parameters, but the lambda from which it was
ultimately regenerated does, so use that instead. */
tree lambda = CLASSTYPE_LAMBDA_EXPR (DECL_CONTEXT (d));
lambda = most_general_lambda (lambda);
d = lambda_function (lambda);
}
if (TREE_CODE (d) == TEMPLATE_DECL)
{
tmpl = d;
@ -3174,12 +3184,26 @@ satisfy_declaration_constraints (tree t, sat_info info)
args = TI_ARGS (ti);
if (inh_ctor_targs)
args = add_outermost_template_args (args, inh_ctor_targs);
}
if (regenerated_lambda_fn_p (t))
{
/* The TI_ARGS of a regenerated lambda contains only the innermost
set of template arguments. Augment this with the outer template
arguments that were used to regenerate the lambda. */
gcc_assert (!args || TMPL_ARGS_DEPTH (args) == 1);
tree lambda = CLASSTYPE_LAMBDA_EXPR (DECL_CONTEXT (t));
tree outer_args = LAMBDA_EXPR_REGENERATING_TARGS (lambda);
if (args)
args = add_to_template_args (outer_args, args);
else
args = outer_args;
}
/* If any arguments depend on template parameters, we can't
check constraints. Pretend they're satisfied for now. */
if (uses_template_parms (args))
return boolean_true_node;
}
/* Get the normalized constraints. */
tree norm = get_normalized_constraints_from_decl (t, info.noisy ());
@ -3227,6 +3251,15 @@ satisfy_declaration_constraints (tree t, tree args, sat_info info)
gcc_assert (TREE_CODE (t) == TEMPLATE_DECL);
if (regenerated_lambda_fn_p (t))
{
/* As in the two-parameter version of this function. */
gcc_assert (TMPL_ARGS_DEPTH (args) == 1);
tree lambda = CLASSTYPE_LAMBDA_EXPR (DECL_CONTEXT (t));
tree outer_args = LAMBDA_EXPR_REGENERATING_TARGS (lambda);
args = add_to_template_args (outer_args, args);
}
else
args = add_outermost_template_args (t, args);
/* If any arguments depend on template parameters, we can't

20
gcc/cp/cp-tree.h
View File

@ -490,7 +490,6 @@ extern GTY(()) tree cp_global_trees[CPTI_MAX];
DECLTYPE_FOR_REF_CAPTURE (in DECLTYPE_TYPE)
CONSTRUCTOR_C99_COMPOUND_LITERAL (in CONSTRUCTOR)
OVL_NESTED_P (in OVERLOAD)
LAMBDA_EXPR_INSTANTIATED (in LAMBDA_EXPR)
DECL_MODULE_EXPORT_P (in _DECL)
4: IDENTIFIER_MARKED (IDENTIFIER_NODEs)
TREE_HAS_CONSTRUCTOR (in INDIRECT_REF, SAVE_EXPR, CONSTRUCTOR,
@ -1434,10 +1433,6 @@ enum cp_lambda_default_capture_mode_type {
#define LAMBDA_EXPR_CAPTURE_OPTIMIZED(NODE) \
TREE_LANG_FLAG_2 (LAMBDA_EXPR_CHECK (NODE))
/* True iff this LAMBDA_EXPR was generated in tsubst_lambda_expr. */
#define LAMBDA_EXPR_INSTANTIATED(NODE) \
TREE_LANG_FLAG_3 (LAMBDA_EXPR_CHECK (NODE))
/* True if this TREE_LIST in LAMBDA_EXPR_CAPTURE_LIST is for an explicit
capture. */
#define LAMBDA_CAPTURE_EXPLICIT_P(NODE) \
@ -1461,6 +1456,16 @@ enum cp_lambda_default_capture_mode_type {
#define LAMBDA_EXPR_PENDING_PROXIES(NODE) \
(((struct tree_lambda_expr *)LAMBDA_EXPR_CHECK (NODE))->pending_proxies)
/* The immediate LAMBDA_EXPR from which NODE was regenerated, or NULL_TREE
(if NODE was not regenerated via tsubst_lambda_expr). */
#define LAMBDA_EXPR_REGENERATED_FROM(NODE) \
(((struct tree_lambda_expr *)LAMBDA_EXPR_CHECK (NODE))->regenerated_from)
/* The full set of template arguments used to regenerate NODE, or NULL_TREE
(if NODE was not regenerated via tsubst_lambda_expr). */
#define LAMBDA_EXPR_REGENERATING_TARGS(NODE) \
(((struct tree_lambda_expr *)LAMBDA_EXPR_CHECK (NODE))->regenerating_targs)
/* The closure type of the lambda, which is also the type of the
LAMBDA_EXPR. */
#define LAMBDA_EXPR_CLOSURE(NODE) \
@ -1472,6 +1477,8 @@ struct GTY (()) tree_lambda_expr
tree capture_list;
tree this_capture;
tree extra_scope;
tree regenerated_from;
tree regenerating_targs;
vec<tree, va_gc> *pending_proxies;
location_t locus;
enum cp_lambda_default_capture_mode_type default_capture_mode : 8;
@ -7247,6 +7254,7 @@ extern unsigned get_mergeable_specialization_flags (tree tmpl, tree spec);
extern void add_mergeable_specialization (bool is_decl, bool is_alias,
spec_entry *,
tree outer, unsigned);
extern tree add_to_template_args (tree, tree);
extern tree add_outermost_template_args (tree, tree);
extern tree add_extra_args (tree, tree);
extern tree build_extra_args (tree, tree, tsubst_flags_t);
@ -7557,6 +7565,8 @@ extern void record_null_lambda_scope (tree);
extern void finish_lambda_scope (void);
extern tree start_lambda_function (tree fn, tree lambda_expr);
extern void finish_lambda_function (tree body);
extern bool regenerated_lambda_fn_p (tree);
extern tree most_general_lambda (tree);
/* in tree.c */
extern int cp_tree_operand_length (const_tree);

2
gcc/cp/lambda.c
View File

@ -41,6 +41,8 @@ build_lambda_expr (void)
LAMBDA_EXPR_DEFAULT_CAPTURE_MODE (lambda) = CPLD_NONE;
LAMBDA_EXPR_CAPTURE_LIST (lambda) = NULL_TREE;
LAMBDA_EXPR_THIS_CAPTURE (lambda) = NULL_TREE;
LAMBDA_EXPR_REGENERATED_FROM (lambda) = NULL_TREE;
LAMBDA_EXPR_REGENERATING_TARGS (lambda) = NULL_TREE;
LAMBDA_EXPR_PENDING_PROXIES (lambda) = NULL;
LAMBDA_EXPR_MUTABLE_P (lambda) = false;
return lambda;

40
gcc/cp/pt.c
View File

@ -151,7 +151,6 @@ static tree coerce_template_parms (tree, tree, tree, tsubst_flags_t,
static tree coerce_innermost_template_parms (tree, tree, tree, tsubst_flags_t,
bool, bool);
static void tsubst_enum (tree, tree, tree);
static tree add_to_template_args (tree, tree);
static bool check_instantiated_args (tree, tree, tsubst_flags_t);
static int check_non_deducible_conversion (tree, tree, int, int,
struct conversion **, bool);
@ -553,7 +552,7 @@ maybe_end_member_template_processing (void)
/* Return a new template argument vector which contains all of ARGS,
but has as its innermost set of arguments the EXTRA_ARGS. */
static tree
tree
add_to_template_args (tree args, tree extra_args)
{
tree new_args;
@ -14065,9 +14064,6 @@ tsubst_function_decl (tree t, tree args, tsubst_flags_t complain,
don't substitute through the constraints; that's only done when
they are checked. */
if (tree ci = get_constraints (t))
/* Unless we're regenerating a lambda, in which case we'll set the
lambda's constraints in tsubst_lambda_expr. */
if (!lambda_fntype)
set_constraints (r, ci);
if (DECL_FRIEND_CONTEXT (t))
@ -14354,13 +14350,24 @@ lambda_fn_in_template_p (tree fn)
which the above is true. */
bool
instantiated_lambda_fn_p (tree fn)
regenerated_lambda_fn_p (tree fn)
{
if (!fn || !LAMBDA_FUNCTION_P (fn))
return false;
tree closure = DECL_CONTEXT (fn);
tree lam = CLASSTYPE_LAMBDA_EXPR (closure);
return LAMBDA_EXPR_INSTANTIATED (lam);
return LAMBDA_EXPR_REGENERATED_FROM (lam) != NULL_TREE;
}
/* Return the LAMBDA_EXPR from which T was ultimately regenerated.
If T is not a regenerated LAMBDA_EXPR, return T. */
tree
most_general_lambda (tree t)
{
while (LAMBDA_EXPR_REGENERATED_FROM (t))
t = LAMBDA_EXPR_REGENERATED_FROM (t);
return t;
}
/* We're instantiating a variable from template function TCTX. Return the
@ -14376,7 +14383,7 @@ enclosing_instantiation_of (tree otctx)
int lambda_count = 0;
for (; tctx && (lambda_fn_in_template_p (tctx)
|| instantiated_lambda_fn_p (tctx));
|| regenerated_lambda_fn_p (tctx));
tctx = decl_function_context (tctx))
++lambda_count;
@ -14396,7 +14403,7 @@ enclosing_instantiation_of (tree otctx)
{
tree ofn = fn;
int flambda_count = 0;
for (; fn && instantiated_lambda_fn_p (fn);
for (; fn && regenerated_lambda_fn_p (fn);
fn = decl_function_context (fn))
++flambda_count;
if ((fn && DECL_TEMPLATE_INFO (fn))
@ -19271,7 +19278,9 @@ tsubst_lambda_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl)
LAMBDA_EXPR_DEFAULT_CAPTURE_MODE (r)
= LAMBDA_EXPR_DEFAULT_CAPTURE_MODE (t);
LAMBDA_EXPR_MUTABLE_P (r) = LAMBDA_EXPR_MUTABLE_P (t);
LAMBDA_EXPR_INSTANTIATED (r) = true;
LAMBDA_EXPR_REGENERATED_FROM (r) = t;
LAMBDA_EXPR_REGENERATING_TARGS (r)
= add_to_template_args (LAMBDA_EXPR_REGENERATING_TARGS (t), args);
gcc_assert (LAMBDA_EXPR_THIS_CAPTURE (t) == NULL_TREE
&& LAMBDA_EXPR_PENDING_PROXIES (t) == NULL);
@ -19413,17 +19422,6 @@ tsubst_lambda_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl)
finish_member_declaration (fn);
}
if (tree ci = get_constraints (oldfn))
{
/* Substitute into the lambda's constraints. */
if (oldtmpl)
++processing_template_decl;
ci = tsubst_constraint_info (ci, args, complain, in_decl);
if (oldtmpl)
--processing_template_decl;
set_constraints (fn, ci);
}
/* Let finish_function set this. */
DECL_DECLARED_CONSTEXPR_P (fn) = false;

61
gcc/testsuite/g++.dg/cpp2a/concepts-lambda16.C Normal file
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@ -0,0 +1,61 @@
// PR c++/99874
// { dg-do compile { target c++20 } }
template <class T>
struct A {
static inline auto a = [] <class U> (U) {
return [] <class V> (V) requires requires (T t, U u, V v) { t + u + v; } { };
};
template <class W>
static inline auto b = [] <class U> (U) {
return [] <class V> (V) requires requires (T t, U u, V v, W w) { t + u + v + w; } { };
};
static auto f() {
return [] <class U> (U) {
return [] <class V> (V) requires requires (T t, U u, V v) { t + u + v; } { };
};
}
template <class W>
static auto g() {
return [] <class U> (U) {
return [] <class V> (V) requires requires (T t, U u, V v, W w) { t + u + v + w; } { };
};
}
};
template <class T>
auto a = [] <class U> (U) {
return [] <class V> (V) requires requires (T t, U u, V v) { t + u + v; } { };
};
template <class T>
auto b = [] <class U> (U) {
return [] <class V> (V) {
return [] {
return [] () requires requires (T t, U u, V v) { t + u + v; } { };
};
};
};
int main() {
A<int>::a(0)(0);
A<int>::a(0)(nullptr); // { dg-error "no match" }
A<int>::b<int>(0)(0);
A<int>::b<int>(0)(nullptr); // { dg-error "no match" }
A<int>::f()(0)(0);
A<int>::f()(0)(nullptr); // { dg-error "no match" }
A<int>::g<int>()(0)(0);
A<int>::g<int>()(0)(nullptr); // { dg-error "no match" }
a<int>(0)(0);
a<int>(0)(nullptr); // { dg-error "no match" }
b<int>(0)(0)();
b<int>(0)(nullptr)()(); // { dg-error "no match" }
}

14
gcc/testsuite/g++.dg/cpp2a/concepts-lambda17.C Normal file
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@ -0,0 +1,14 @@
// { dg-do compile { target c++20 } }
template<class T>
struct A { static const bool value = T::value; };
template<class T>
void f() {
// Verify we don't substitute into a lambda's constraints when
// regenerating it, which would lead to a hard error here.
[] () requires (T::value && A<T>::value) || true { }();
[] <class U> (U) requires (U::value && A<T>::value) || true { }(0);
}
template void f<int>();