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* [gcc r12-7564] c++: non-constant non-dependent decltype folding [PR104823]
@ 2022-03-09 13:44 Patrick Palka
0 siblings, 0 replies; only message in thread
From: Patrick Palka @ 2022-03-09 13:44 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:ec0f53a3a542e762f8fc8c22b9d345f922be5867
commit r12-7564-gec0f53a3a542e762f8fc8c22b9d345f922be5867
Author: Patrick Palka <ppalka@redhat.com>
Date: Wed Mar 9 08:42:37 2022 -0500
c++: non-constant non-dependent decltype folding [PR104823]
When processing a non-dependent decltype operand we want to instantiate
it even if it's non-constant, since non-dependent decltype is always
resolved ahead of time. But currently finish_decltype_type uses
instantiate_non_dependent_expr, which instantiates only potentially
constant expressions, and this causes us to miss diagnosing the narrowing
conversion in S{id(v)} in the below testcase because we never instantiate
this non-constant non-dependent decltype operand.
In light of
> On Mon, 7 Mar 2022, Jason Merrill wrote:
>> On 3/7/22 14:41, Patrick Palka wrote:
>>> instantiate_non_dependent_expr instantiates only potentially constant
>>> expressions
>>
>> Hmm, that now strikes me as a problematic interface, as we don't know whether
>> what we get back is template or non-template trees.
this patch drops the potentially-constant check in i_n_d_e and turns
its dependence check into a checking_assert, since most callers already
check that the argument is non-dependent; thus i_n_d_e now instantiates
even non-constant expressions and always returns non-templated trees.
This patch also relaxes the dependence check in i_n_d_e to use the
_uneval version (since that's what finish_decltype_type uses) and
strengthens the dependence checks used by other callers accordingly.
In cp_parser_parenthesized_expression_list_elt we were calling
instantiate_non_dependent_expr (when parsing an attribute list) without
first checking for non-dependence. We could fix this by guarding the
call appropriately, but I noticed we also fold non-dependent attributes
later from cp_check_const_attribute, so this earlier folding is at best
redundant. And it currently causes us to reject constexpr-attribute4.C
below due to the second folding seeing non-templated trees. Thus the
right solution here seems to be to remove this unguarded call to i_n_d_e
so that we end up instantiating non-dependent attributes only once.
Finally, after calling i_n_d_e in finish_decltype_type we need to keep
processing_template_decl cleared for sake of the later call to
lvalue_kind, which handles templated and non-templated COND_EXPR
differently. Otherwise we'd incorrectly reject the declaration of g in
cpp0x/cond2.C with:
error: 'g' declared as function returning a function
PR c++/104823
gcc/cp/ChangeLog:
* except.cc (build_noexcept_spec): Strengthen dependence check
to instantiation_dependent_expression_p.
* parser.cc (cp_parser_parenthesized_expression_list_elt):
Remove fold_expr_p parameter, and don't call
instantiate_non_dependent_expr.
(cp_parser_parenthesized_expression_list): Adjust accordingly.
* pt.cc (expand_integer_pack): Strengthen dependence check
to instantiation_dependent_expression_p.
(instantiate_non_dependent_expr_internal): Adjust comment.
(instantiate_non_dependent_expr_sfinae): Likewise. Drop
the potentially-constant check, and relax and turn the
dependence check into a checking assert.
(instantiate_non_dependent_or_null): Adjust comment.
* semantics.cc (finish_decltype_type): Keep
processing_template_decl cleared after calling
instantiate_non_dependent_expr_sfinae.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/Wnarrowing19.C: New test.
Diff:
---
gcc/cp/except.cc | 2 +-
gcc/cp/parser.cc | 8 --------
gcc/cp/pt.cc | 25 ++++++++---------------
gcc/cp/semantics.cc | 6 ++++++
gcc/testsuite/g++.dg/cpp0x/Wnarrowing19.C | 6 ++++++
gcc/testsuite/g++.dg/cpp0x/constexpr-attribute4.C | 14 +++++++++++++
6 files changed, 35 insertions(+), 26 deletions(-)
diff --git a/gcc/cp/except.cc b/gcc/cp/except.cc
index 9b746be231a..da0a65c613d 100644
--- a/gcc/cp/except.cc
+++ b/gcc/cp/except.cc
@@ -1253,7 +1253,7 @@ build_noexcept_spec (tree expr, tsubst_flags_t complain)
if (check_for_bare_parameter_packs (expr))
return error_mark_node;
if (TREE_CODE (expr) != DEFERRED_NOEXCEPT
- && !value_dependent_expression_p (expr))
+ && !instantiation_dependent_expression_p (expr))
{
expr = build_converted_constant_bool_expr (expr, complain);
expr = instantiate_non_dependent_expr_sfinae (expr, complain);
diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 9153c74f069..5c342ca631b 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -7958,7 +7958,6 @@ cp_parser_postfix_expression (cp_parser *parser, bool address_p, bool cast_p,
static cp_expr
cp_parser_parenthesized_expression_list_elt (cp_parser *parser, bool cast_p,
bool allow_expansion_p,
- bool fold_expr_p,
bool *non_constant_p)
{
cp_expr expr (NULL_TREE);
@@ -7985,9 +7984,6 @@ cp_parser_parenthesized_expression_list_elt (cp_parser *parser, bool cast_p,
else
expr = cp_parser_assignment_expression (parser, /*pidk=*/NULL, cast_p);
- if (fold_expr_p)
- expr = instantiate_non_dependent_expr (expr);
-
/* If we have an ellipsis, then this is an expression expansion. */
if (allow_expansion_p
&& cp_lexer_next_token_is (parser->lexer, CPP_ELLIPSIS))
@@ -8053,8 +8049,6 @@ cp_parser_postfix_open_square_expression (cp_parser *parser,
false,
/*allow_exp_p=*/
true,
- /*fold_expr_p=*/
- false,
/*non_cst_p=*/
NULL);
@@ -8424,7 +8418,6 @@ cp_parser_parenthesized_expression_list (cp_parser* parser,
bool wrap_locations_p)
{
vec<tree, va_gc> *expression_list;
- bool fold_expr_p = is_attribute_list != non_attr;
tree identifier = NULL_TREE;
bool saved_greater_than_is_operator_p;
@@ -8467,7 +8460,6 @@ cp_parser_parenthesized_expression_list (cp_parser* parser,
expr
= cp_parser_parenthesized_expression_list_elt (parser, cast_p,
allow_expansion_p,
- fold_expr_p,
non_constant_p);
if (wrap_locations_p)
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index f8069b2ea0e..f7ee33a6dfd 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -3817,7 +3817,7 @@ expand_integer_pack (tree call, tree args, tsubst_flags_t complain,
tree hi = tsubst_copy_and_build (ohi, args, complain, in_decl,
false/*fn*/, true/*int_cst*/);
- if (value_dependent_expression_p (hi))
+ if (instantiation_dependent_expression_p (hi))
{
if (hi != ohi)
{
@@ -6349,9 +6349,7 @@ redeclare_class_template (tree type, tree parms, tree cons)
/* The actual substitution part of instantiate_non_dependent_expr_sfinae,
to be used when the caller has already checked
- (processing_template_decl
- && !instantiation_dependent_expression_p (expr)
- && potential_constant_expression (expr))
+ !instantiation_dependent_uneval_expression_p (expr)
and cleared processing_template_decl. */
tree
@@ -6365,8 +6363,7 @@ instantiate_non_dependent_expr_internal (tree expr, tsubst_flags_t complain)
/*integral_constant_expression_p=*/true);
}
-/* Simplify EXPR if it is a non-dependent expression. Returns the
- (possibly simplified) expression. */
+/* Instantiate the non-dependent expression EXPR. */
tree
instantiate_non_dependent_expr_sfinae (tree expr, tsubst_flags_t complain)
@@ -6374,16 +6371,10 @@ instantiate_non_dependent_expr_sfinae (tree expr, tsubst_flags_t complain)
if (expr == NULL_TREE)
return NULL_TREE;
- /* If we're in a template, but EXPR isn't value dependent, simplify
- it. We're supposed to treat:
-
- template <typename T> void f(T[1 + 1]);
- template <typename T> void f(T[2]);
-
- as two declarations of the same function, for example. */
- if (processing_template_decl
- && is_nondependent_constant_expression (expr))
+ if (processing_template_decl)
{
+ /* The caller should have checked this already. */
+ gcc_checking_assert (!instantiation_dependent_uneval_expression_p (expr));
processing_template_decl_sentinel s;
expr = instantiate_non_dependent_expr_internal (expr, complain);
}
@@ -6396,8 +6387,8 @@ instantiate_non_dependent_expr (tree expr)
return instantiate_non_dependent_expr_sfinae (expr, tf_error);
}
-/* Like instantiate_non_dependent_expr, but return NULL_TREE rather than
- an uninstantiated expression. */
+/* Like instantiate_non_dependent_expr, but return NULL_TREE if the
+ expression is dependent or non-constant. */
tree
instantiate_non_dependent_or_null (tree expr)
diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index a2c0eb050e6..799ce943279 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -11217,6 +11217,8 @@ finish_decltype_type (tree expr, bool id_expression_or_member_access_p,
/* decltype is an unevaluated context. */
cp_unevaluated u;
+ processing_template_decl_sentinel ptds (/*reset=*/false);
+
/* Depending on the resolution of DR 1172, we may later need to distinguish
instantiation-dependent but not type-dependent expressions so that, say,
A<decltype(sizeof(T))>::U doesn't require 'typename'. */
@@ -11235,6 +11237,10 @@ finish_decltype_type (tree expr, bool id_expression_or_member_access_p,
expr = instantiate_non_dependent_expr_sfinae (expr, complain);
if (expr == error_mark_node)
return error_mark_node;
+ /* Keep processing_template_decl cleared for the rest of the function
+ (for sake of the call to lvalue_kind below, which handles templated
+ and non-templated COND_EXPR differently). */
+ processing_template_decl = 0;
}
/* The type denoted by decltype(e) is defined as follows: */
diff --git a/gcc/testsuite/g++.dg/cpp0x/Wnarrowing19.C b/gcc/testsuite/g++.dg/cpp0x/Wnarrowing19.C
new file mode 100644
index 00000000000..77357016502
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/Wnarrowing19.C
@@ -0,0 +1,6 @@
+// PR c++/104823
+// { dg-do compile { target c++11 } }
+
+struct S { S(int); };
+double id(double);
+template<class> auto f(double v) -> decltype(S{id(v)}); // { dg-error "narrowing" }
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-attribute4.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-attribute4.C
new file mode 100644
index 00000000000..c52d58f8d32
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-attribute4.C
@@ -0,0 +1,14 @@
+// Verify we correctly handle the non-dependent attribute expression which
+// which we used to reject due to double folding.
+// { dg-do compile { target { c++11 } } }
+
+struct A {
+ constexpr int f() const { return __alignof__(int); };
+};
+
+template<class...>
+void f() {
+ int a __attribute__((aligned(A{}.f())));
+}
+
+template void f();
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