On Mon, 25 Mar 2024, Patrick Palka wrote:
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK
> for trunk?
>
> -- >8 --
>
> The below testcases use a lambda-expr as a template argument and they
> all trip over the below added tsubst_lambda_expr sanity check ultimately
> because current_template_parms is empty, which causes push_template_decl
> to return error_mark_node from the call to begin_lambda_type. Were it
> not for the sanity check this silent error_mark_node result leads to
> nonsensical errors down the line, or silent breakage.
>
> In the first testcase, we hit this assert during instantiation of the
> dependent alias template-id c1_t<_Data> from instantiate_template, which
> clears current_template_parms via push_to_top_level. Similar story for
> the second testcase. For the third testcase we hit the assert during
> partial instantiation of the member template from instantiate_class_template
> which similarly calls push_to_top_level.
>
> These testcases illustrate that templated substitution into a lambda-expr
> is not always possible, in particular when we lost the relevant template
> context. I experimented with recovering the template context by making
> tsubst_lambda_expr fall back to using scope_chain->prev->template_parms if
> current_template_parms is empty which worked but seemed like a hack. I
> also experimented with preserving the template context by keeping
> current_template_parms set during instantiate_template for a dependent
> specialization which also worked but it's at odds with the fact that we
> cache dependent specializations (and so they should be independent of
> the template context).
>
> So instead of trying to make such substitution work, this patch uses the
> extra-args mechanism to defer templated substitution into a lambda-expr
> when we lost the relevant template context.
>
> PR c++/114393
> PR c++/107457
> PR c++/93595
>
> gcc/cp/ChangeLog:
>
> * cp-tree.h (LAMBDA_EXPR_EXTRA_ARGS):
> (struct GTY):
> * module.cc (trees_out::core_vals) <case LAMBDA_EXPR>: Stream
> LAMBDA_EXPR_EXTRA_ARGS.
> (trees_in::core_vals) <case LAMBDA_EXPR>: Likewise.
> * pt.cc (has_extra_args_mechanism_p):
> (tsubst_lambda_expr):
Whoops, this version of the patch has an incomplete ChangeLog entry.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/cpp2a/lambda-targ2.C: New test.
> * g++.dg/cpp2a/lambda-targ3.C: New test.
> * g++.dg/cpp2a/lambda-targ4.C: New test.
> ---
> gcc/cp/cp-tree.h | 5 +++++
> gcc/cp/module.cc | 2 ++
> gcc/cp/pt.cc | 20 ++++++++++++++++++--
> gcc/testsuite/g++.dg/cpp2a/lambda-targ2.C | 19 +++++++++++++++++++
> gcc/testsuite/g++.dg/cpp2a/lambda-targ3.C | 12 ++++++++++++
> gcc/testsuite/g++.dg/cpp2a/lambda-targ4.C | 12 ++++++++++++
> 6 files changed, 68 insertions(+), 2 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/cpp2a/lambda-targ2.C
> create mode 100644 gcc/testsuite/g++.dg/cpp2a/lambda-targ3.C
> create mode 100644 gcc/testsuite/g++.dg/cpp2a/lambda-targ4.C
>
> diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
> index c29a5434492..27100537038 100644
> --- a/gcc/cp/cp-tree.h
> +++ b/gcc/cp/cp-tree.h
> @@ -1538,6 +1538,10 @@ enum cp_lambda_default_capture_mode_type {
> #define LAMBDA_EXPR_REGEN_INFO(NODE) \
> (((struct tree_lambda_expr *)LAMBDA_EXPR_CHECK (NODE))->regen_info)
>
> +/* Like PACK_EXPANSION_EXTRA_ARGS, for lambda-expressions. */
> +#define LAMBDA_EXPR_EXTRA_ARGS(NODE) \
> + (((struct tree_lambda_expr *)LAMBDA_EXPR_CHECK (NODE))->extra_args)
> +
> /* The closure type of the lambda, which is also the type of the
> LAMBDA_EXPR. */
> #define LAMBDA_EXPR_CLOSURE(NODE) \
> @@ -1550,6 +1554,7 @@ struct GTY (()) tree_lambda_expr
> tree this_capture;
> tree extra_scope;
> tree regen_info;
> + tree extra_args;
> vec<tree, va_gc> *pending_proxies;
> location_t locus;
> enum cp_lambda_default_capture_mode_type default_capture_mode : 2;
> diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
> index 52c60cf370c..1cd890909e3 100644
> --- a/gcc/cp/module.cc
> +++ b/gcc/cp/module.cc
> @@ -6312,6 +6312,7 @@ trees_out::core_vals (tree t)
> WT (((lang_tree_node *)t)->lambda_expression.this_capture);
> WT (((lang_tree_node *)t)->lambda_expression.extra_scope);
> WT (((lang_tree_node *)t)->lambda_expression.regen_info);
> + WT (((lang_tree_node *)t)->lambda_expression.extra_args);
> /* pending_proxies is a parse-time thing. */
> gcc_assert (!((lang_tree_node *)t)->lambda_expression.pending_proxies);
> if (state)
> @@ -6814,6 +6815,7 @@ trees_in::core_vals (tree t)
> RT (((lang_tree_node *)t)->lambda_expression.this_capture);
> RT (((lang_tree_node *)t)->lambda_expression.extra_scope);
> RT (((lang_tree_node *)t)->lambda_expression.regen_info);
> + RT (((lang_tree_node *)t)->lambda_expression.extra_args);
> /* lambda_expression.pending_proxies is NULL */
> ((lang_tree_node *)t)->lambda_expression.locus
> = state->read_location (*this);
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index 8cf0d5b7a8d..b1a9ee2b385 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -3855,7 +3855,8 @@ has_extra_args_mechanism_p (const_tree t)
> return (PACK_EXPANSION_P (t) /* PACK_EXPANSION_EXTRA_ARGS */
> || TREE_CODE (t) == REQUIRES_EXPR /* REQUIRES_EXPR_EXTRA_ARGS */
> || (TREE_CODE (t) == IF_STMT
> - && IF_STMT_CONSTEXPR_P (t))); /* IF_STMT_EXTRA_ARGS */
> + && IF_STMT_CONSTEXPR_P (t)) /* IF_STMT_EXTRA_ARGS */
> + || TREE_CODE (t) == LAMBDA_EXPR) /* LAMBDA_EXPR_EXTRA_ARGS */;
> }
>
> /* Structure used to track the progress of find_parameter_packs_r. */
> @@ -19571,6 +19572,18 @@ tsubst_lambda_expr (tree t, tree args,
> tsubst_flags_t complain, tree in_decl)
> tree oldfn = lambda_function (t);
> in_decl = oldfn;
>
> + args = add_extra_args (LAMBDA_EXPR_EXTRA_ARGS (t), args, complain,
> in_decl);
> + if (processing_template_decl && !in_template_context)
> + {
> + /* Defer templated substitution into a lambda-expr when arguments
> + are dependent or when we lost the necessary template context,
> + which may happen for a lambda-expr used as a template argument. */
And this comment is stale (an earlier version of the patch also deferred
for dependent arguments even when current_template_parms is non-empty,
which I backed out to make the fix as narrow as possible).
Better version:
-- >8 --
Subject: [PATCH] c++: templated substitution into lambda-expr [PR114393]
PR c++/114393
PR c++/107457
PR c++/93595
gcc/cp/ChangeLog:
* cp-tree.h (LAMBDA_EXPR_EXTRA_ARGS): Define.
(tree_lambda_expr::extra_args): New field.
* module.cc (trees_out::core_vals) <case LAMBDA_EXPR>: Stream
LAMBDA_EXPR_EXTRA_ARGS.
(trees_in::core_vals) <case LAMBDA_EXPR>: Likewise.
* pt.cc (has_extra_args_mechanism_p): Return true for LAMBDA_EXPR.
(tsubst_lambda_expr): Use LAMBDA_EXPR_EXTRA_ARGS to defer templated
substitution into a lambda-expr if we lost the template context.
Add sanity check for error_mark_node result from begin_lambda_type.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/lambda-targ2.C: New test.
* g++.dg/cpp2a/lambda-targ3.C: New test.
* g++.dg/cpp2a/lambda-targ4.C: New test.
---
gcc/cp/cp-tree.h | 5 +++++
gcc/cp/module.cc | 2 ++
gcc/cp/pt.cc | 20 ++++++++++++++++++--
gcc/testsuite/g++.dg/cpp2a/lambda-targ2.C | 19 +++++++++++++++++++
gcc/testsuite/g++.dg/cpp2a/lambda-targ3.C | 12 ++++++++++++
gcc/testsuite/g++.dg/cpp2a/lambda-targ4.C | 12 ++++++++++++
6 files changed, 68 insertions(+), 2 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/lambda-targ2.C
create mode 100644 gcc/testsuite/g++.dg/cpp2a/lambda-targ3.C
create mode 100644 gcc/testsuite/g++.dg/cpp2a/lambda-targ4.C
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index c29a5434492..27100537038 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -1538,6 +1538,10 @@ enum cp_lambda_default_capture_mode_type {
#define LAMBDA_EXPR_REGEN_INFO(NODE) \
(((struct tree_lambda_expr *)LAMBDA_EXPR_CHECK (NODE))->regen_info)
+/* Like PACK_EXPANSION_EXTRA_ARGS, for lambda-expressions. */
+#define LAMBDA_EXPR_EXTRA_ARGS(NODE) \
+ (((struct tree_lambda_expr *)LAMBDA_EXPR_CHECK (NODE))->extra_args)
+
/* The closure type of the lambda, which is also the type of the
LAMBDA_EXPR. */
#define LAMBDA_EXPR_CLOSURE(NODE) \
@@ -1550,6 +1554,7 @@ struct GTY (()) tree_lambda_expr
tree this_capture;
tree extra_scope;
tree regen_info;
+ tree extra_args;
vec<tree, va_gc> *pending_proxies;
location_t locus;
enum cp_lambda_default_capture_mode_type default_capture_mode : 2;
diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index 52c60cf370c..1cd890909e3 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -6312,6 +6312,7 @@ trees_out::core_vals (tree t)
WT (((lang_tree_node *)t)->lambda_expression.this_capture);
WT (((lang_tree_node *)t)->lambda_expression.extra_scope);
WT (((lang_tree_node *)t)->lambda_expression.regen_info);
+ WT (((lang_tree_node *)t)->lambda_expression.extra_args);
/* pending_proxies is a parse-time thing. */
gcc_assert (!((lang_tree_node *)t)->lambda_expression.pending_proxies);
if (state)
@@ -6814,6 +6815,7 @@ trees_in::core_vals (tree t)
RT (((lang_tree_node *)t)->lambda_expression.this_capture);
RT (((lang_tree_node *)t)->lambda_expression.extra_scope);
RT (((lang_tree_node *)t)->lambda_expression.regen_info);
+ RT (((lang_tree_node *)t)->lambda_expression.extra_args);
/* lambda_expression.pending_proxies is NULL */
((lang_tree_node *)t)->lambda_expression.locus
= state->read_location (*this);
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 8cf0d5b7a8d..c25bdd283f1 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -3855,7 +3855,8 @@ has_extra_args_mechanism_p (const_tree t)
return (PACK_EXPANSION_P (t) /* PACK_EXPANSION_EXTRA_ARGS */
|| TREE_CODE (t) == REQUIRES_EXPR /* REQUIRES_EXPR_EXTRA_ARGS */
|| (TREE_CODE (t) == IF_STMT
- && IF_STMT_CONSTEXPR_P (t))); /* IF_STMT_EXTRA_ARGS */
+ && IF_STMT_CONSTEXPR_P (t)) /* IF_STMT_EXTRA_ARGS */
+ || TREE_CODE (t) == LAMBDA_EXPR) /* LAMBDA_EXPR_EXTRA_ARGS */;
}
/* Structure used to track the progress of find_parameter_packs_r. */
@@ -19571,6 +19572,18 @@ tsubst_lambda_expr (tree t, tree args, tsubst_flags_t
complain, tree in_decl)
tree oldfn = lambda_function (t);
in_decl = oldfn;
+ args = add_extra_args (LAMBDA_EXPR_EXTRA_ARGS (t), args, complain, in_decl);
+ if (processing_template_decl && !in_template_context)
+ {
+ /* Defer templated substitution into a lambda-expr when we lost the
+ necessary template context, which may happen for a lambda-expr
+ used as a template argument. */
+ t = copy_node (t);
+ LAMBDA_EXPR_EXTRA_ARGS (t) = NULL_TREE;
+ LAMBDA_EXPR_EXTRA_ARGS (t) = build_extra_args (t, args, complain);
+ return t;
+ }
+
tree r = build_lambda_expr ();
LAMBDA_EXPR_LOCATION (r)
@@ -19662,7 +19675,10 @@ tsubst_lambda_expr (tree t, tree args, tsubst_flags_t
complain, tree in_decl)
tree type = begin_lambda_type (r);
if (type == error_mark_node)
- return error_mark_node;
+ {
+ gcc_checking_assert (!(complain & tf_error) || seen_error ());
+ return error_mark_node;
+ }
if (LAMBDA_EXPR_EXTRA_SCOPE (t))
record_lambda_scope (r);
diff --git a/gcc/testsuite/g++.dg/cpp2a/lambda-targ2.C
b/gcc/testsuite/g++.dg/cpp2a/lambda-targ2.C
new file mode 100644
index 00000000000..41b8d8749f2
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/lambda-targ2.C
@@ -0,0 +1,19 @@
+// PR c++/114393
+// { dg-do compile { target c++20 } }
+
+template <auto _DescriptorFn> struct c1 {};
+
+template <class _Descriptor, auto t = [] { return _Descriptor(); }>
+inline constexpr auto b_v = t;
+
+template <class _Tag>
+using c1_t = c1<b_v<int>>;
+
+template <class _Data>
+constexpr auto g(_Data __data) {
+ return c1_t<_Data>{};
+}
+
+void f() {
+ auto &&b = g(0);
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/lambda-targ3.C
b/gcc/testsuite/g++.dg/cpp2a/lambda-targ3.C
new file mode 100644
index 00000000000..31d08add277
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/lambda-targ3.C
@@ -0,0 +1,12 @@
+// PR c++/107457
+// { dg-do compile { target c++20 } }
+
+template<class T>
+using lambda = decltype([]() {});
+
+template<class R, class F = lambda<R>>
+void test() { }
+
+int main() {
+ test<int>();
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/lambda-targ4.C
b/gcc/testsuite/g++.dg/cpp2a/lambda-targ4.C
new file mode 100644
index 00000000000..341a1aa5bb1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/lambda-targ4.C
@@ -0,0 +1,12 @@
+// PR c++/93595
+// { dg-do compile { target c++20 } }
+
+template<int>
+struct bad {
+ template<class T, auto = []{ return T(); }>
+ static void f(T) { }
+};
+
+int main() {
+ bad<0>::f(0);
+}
--
2.44.0.325.g11c821f2f2
