On 7/8/21 11:28 AM, Patrick Palka wrote:
Here we're crashing ultimately because the mechanism for delaying
substitution into a requires-expression (or constexpr if) doesn't
expect to see dependent args. But we end up capturing dependent
args here when substituting into the default template argument during
coerce_template_parms for the dependent specialization p<T>.
This patch enables the commented out code in add_extra_args for
handling this situation. It turns out we also need to make a copy of
the captured arguments so that coerce_template_parms doesn't later
add to the argument, which would form an unexpected cycle. And we
need to make tsubst_template_args more forgiving about missing template
arguments, since the arguments we capture from coerce_template_parms are
incomplete.
Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk/11?
PR c++/101181
gcc/cp/ChangeLog:
* constraint.cc (tsubst_requires_expr): Pass complain/in_decl to
add_extra_args.
* cp-tree.h (add_extra_args): Add complain/in_decl parameters.
* pt.c (build_extra_args): Make a copy of args.
(add_extra_args): Add complain/in_decl parameters. Handle the
case where the extra arguments are dependent.
(tsubst_pack_expansion): Pass complain/in_decl to
add_extra_args.
(tsubst_template_args): Handle missing template arguments.
(tsubst_expr) <case IF_STMT>: Pass complain/in_decl to
add_extra_args.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/concepts-requires26.C: New test.
* g++.dg/cpp2a/lambda-uneval16.C: New test.
---
gcc/cp/constraint.cc | 3 +-
gcc/cp/cp-tree.h | 2 +-
gcc/cp/pt.c | 31 +++++++++----------
.../g++.dg/cpp2a/concepts-requires26.C | 18 +++++++++++
gcc/testsuite/g++.dg/cpp2a/lambda-uneval16.C | 22 +++++++++++++
5 files changed, 58 insertions(+), 18 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-requires26.C
create mode 100644 gcc/testsuite/g++.dg/cpp2a/lambda-uneval16.C
diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index 99d3ccc6998..4ee5215df50 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -2266,7 +2266,8 @@ tsubst_requires_expr (tree t, tree args, sat_info info)
/* A requires-expression is an unevaluated context. */
cp_unevaluated u;
- args = add_extra_args (REQUIRES_EXPR_EXTRA_ARGS (t), args);
+ args = add_extra_args (REQUIRES_EXPR_EXTRA_ARGS (t), args,
+ info.complain, info.in_decl);
if (processing_template_decl)
{
/* We're partially instantiating a generic lambda. Substituting into
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 58da7460001..0a5f13489cc 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -7289,7 +7289,7 @@ extern void add_mergeable_specialization (bool
is_decl, bool is_alias,
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 add_extra_args (tree, tree, tsubst_flags_t,
tree);
extern tree build_extra_args (tree, tree, tsubst_flags_t);
/* in rtti.c */
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 06116d16887..e4bdac087ad 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -12928,7 +12928,9 @@ extract_local_specs (tree pattern, tsubst_flags_t
complain)
tree
build_extra_args (tree pattern, tree args, tsubst_flags_t complain)
{
- tree extra = args;
+ /* Make a copy of the extra arguments so that they won't get changed
+ from under us. */
+ tree extra = copy_template_args (args);
if (local_specializations)
if (tree locals = extract_local_specs (pattern, complain))
extra = tree_cons (NULL_TREE, extra, locals);
@@ -12939,7 +12941,7 @@ build_extra_args (tree pattern, tree args,
tsubst_flags_t complain)
normal template args to ARGS. */
tree
-add_extra_args (tree extra, tree args)
+add_extra_args (tree extra, tree args, tsubst_flags_t complain, tree in_decl)
{
if (extra && TREE_CODE (extra) == TREE_LIST)
{
@@ -12959,20 +12961,14 @@ add_extra_args (tree extra, tree args)
gcc_assert (!TREE_PURPOSE (extra));
extra = TREE_VALUE (extra);
}
-#if 1
- /* I think we should always be able to substitute dependent args into the
- pattern. If that turns out to be incorrect in some cases, enable the
- alternate code (and add complain/in_decl parms to this function). */
Ah, because these cases aren't pack expansions, so we aren't trying to
do the substitution; I wonder if it would be feasible to do so. But
this approach is probably simpler. OK.
- gcc_checking_assert (!uses_template_parms (extra));
-#else
- if (!uses_template_parms (extra))
+ if (uses_template_parms (extra))
{
- gcc_unreachable ();
+ /* This can happen during dependent substitution into a requires-expr
+ or a lambda that uses constexpr if. */
extra = tsubst_template_args (extra, args, complain, in_decl);
args = add_outermost_template_args (args, extra);
}
else
-#endif
args = add_to_template_args (extra, args);
return args;
}
@@ -12998,7 +12994,7 @@ tsubst_pack_expansion (tree t, tree args,
tsubst_flags_t complain,
pattern = PACK_EXPANSION_PATTERN (t);
/* Add in any args remembered from an earlier partial instantiation. */
- args = add_extra_args (PACK_EXPANSION_EXTRA_ARGS (t), args);
+ args = add_extra_args (PACK_EXPANSION_EXTRA_ARGS (t), args, complain,
in_decl);
levels = TMPL_ARGS_DEPTH (args);
@@ -13370,7 +13366,9 @@ tsubst_template_args (tree t, tree args, tsubst_flags_t complain, tree in_decl)
tree orig_arg = TREE_VEC_ELT (t, i);
tree new_arg;
- if (TREE_CODE (orig_arg) == TREE_VEC)
+ if (!orig_arg)
+ new_arg = NULL_TREE;
+ else if (TREE_CODE (orig_arg) == TREE_VEC)
new_arg = tsubst_template_args (orig_arg, args, complain, in_decl);
else if (PACK_EXPANSION_P (orig_arg))
{
@@ -13420,8 +13418,9 @@ tsubst_template_args (tree t, tree args, tsubst_flags_t
complain, tree in_decl)
}
for (i = 0, out = 0; i < len; i++)
{
- if ((PACK_EXPANSION_P (TREE_VEC_ELT (orig_t, i))
- || ARGUMENT_PACK_P (TREE_VEC_ELT (orig_t, i)))
+ tree orig_arg = TREE_VEC_ELT (orig_t, i);
+ if (orig_arg
+ && (PACK_EXPANSION_P (orig_arg) || ARGUMENT_PACK_P (orig_arg))
&& TREE_CODE (elts[i]) == TREE_VEC)
{
int idx;
@@ -18449,7 +18448,7 @@ tsubst_expr (tree t, tree args, tsubst_flags_t
complain, tree in_decl,
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);
+ args = add_extra_args (IF_STMT_EXTRA_ARGS (t), args, complain, in_decl);
tmp = RECUR (IF_COND (t));
tmp = finish_if_stmt_cond (tmp, stmt);
if (IF_STMT_CONSTEXPR_P (t)
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-requires26.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-requires26.C
new file mode 100644
index 00000000000..824d23431f0
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-requires26.C
@@ -0,0 +1,18 @@
+// PR c++/101181
+// { dg-do compile { target c++20 } }
+
+template<class T,
+ bool = requires { typename T::type; }>
+struct p { using type = void; };
+
+template<class T>
+struct p<T, true> { using type = typename T::type; };
+
+template<class T> using P = typename p<T>::type;
+
+using type1 = P<int>;
+using type1 = void;
+
+struct A { using type = char; };
+using type2 = P<A>;
+using type2 = char;
diff --git a/gcc/testsuite/g++.dg/cpp2a/lambda-uneval16.C
b/gcc/testsuite/g++.dg/cpp2a/lambda-uneval16.C
new file mode 100644
index 00000000000..1113c6f02b9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/lambda-uneval16.C
@@ -0,0 +1,22 @@
+// PR c++/101181
+// { dg-do compile { target c++20 } }
+
+template<class T,
+ bool = [] () -> bool {
+ if constexpr (requires { typename T::type; })
+ return true;
+ return false;
+ }()>
+struct p { using type = void; };
+
+template<class T>
+struct p<T, true> { using type = typename T::type; };
+
+template<class T> using P = typename p<T>::type;
+
+using type1 = P<int>;
+using type = void;
+
+struct A { using type = char; };
+using type2 = P<A>;
+using type2 = char;
