This PR points out an ICE with an alias template and class NTTP, but I
found that there are more issues. Trouble arise when we use a
(non-type) template parameter as an argument to the template arg list of
a template that accepts a class NTTP and a conversion to a class is
involved, e.g.
struct A { A(int) { } };
template<A a> struct B { };
template<int X> void fn () {
B<X> b;
}
Normally for such a conversion we create a TARGET_EXPR with an
AGGR_INIT_EXPR that calls a __ct_comp with some arguments, but not in
this case: when converting X to type A in convert_nontype_argument we
are in a template and the template parameter 'X' is value-dependent, and
AGGR_INIT_EXPR don't work in templates. So it just creates a TARGET_EXPR
that contains "A::A(*this, X)", but with that overload resolution fails:
error: no matching function for call to 'A::A(A*, int)'
That happens because finish_call_expr for a BASELINK creates a dummy
object, so we have 'this' twice. I thought for the value-dependent case
we could use IMPLICIT_CONV_EXPR, as in the patch below. Note that I
only do this when we convert to a different type than the type of the
expr. The point is to avoid the call to a converting ctor.
The second issue was an ICE in tsubst_copy: when there's a conversion
like the above involved then
/* Wrapper to make a C++20 template parameter object const. */
op = tsubst_copy (op, args, complain, in_decl);
might not produce a _ZT... VAR_DECL with const type, so the assert
gcc_assert (CP_TYPE_CONST_P (TREE_TYPE (op)));
fails. Allowing IMPLICIT_CONV_EXPR there probably makes sense.
And since convert_nontype_argument uses value_dependent_expression_p
a lot, I used a dedicated bool to speed things up.
Bootstrapped/regtested on x86_64-linux, ok for trunk and maybe 9?
2020-01-28 Marek Polacek <pola...@redhat.com>
PR c++/92948 - Fix class NTTP with template arguments.
* pt.c (convert_nontype_argument): Use IMPLICIT_CONV_EXPR when
converting a value-dependent expression to a class type.
(tsubst_copy) <case VIEW_CONVERT_EXPR>: Allow IMPLICIT_CONV_EXPR
as the result of the tsubst_copy call.
* g++.dg/cpp2a/nontype-class28.C: New test.
* g++.dg/cpp2a/nontype-class29.C: New test.
---
gcc/cp/pt.c | 36 +++++++++++--------
gcc/testsuite/g++.dg/cpp2a/nontype-class28.C | 37 ++++++++++++++++++++
gcc/testsuite/g++.dg/cpp2a/nontype-class29.C | 26 ++++++++++++++
3 files changed, 85 insertions(+), 14 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/nontype-class28.C
create mode 100644 gcc/testsuite/g++.dg/cpp2a/nontype-class29.C
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index e889c800aca..fccf4e95453 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -7074,7 +7074,8 @@ convert_nontype_argument (tree type, tree expr,
tsubst_flags_t complain)
if (non_dep)
expr = instantiate_non_dependent_expr_internal (expr, complain);
- if (value_dependent_expression_p (expr))
+ const bool val_dep_p = value_dependent_expression_p (expr);
+ if (val_dep_p)
expr = canonicalize_expr_argument (expr, complain);
/* 14.3.2/5: The null pointer{,-to-member} conversion is applied
@@ -7100,10 +7101,17 @@ convert_nontype_argument (tree type, tree expr,
tsubst_flags_t complain)
a conversion function with a value-dependent argument, which
could invoke taking the address of a temporary representing
the result of the conversion. */
- if (COMPOUND_LITERAL_P (expr)
- && CONSTRUCTOR_IS_DEPENDENT (expr)
- && MAYBE_CLASS_TYPE_P (expr_type)
- && TYPE_HAS_CONVERSION (expr_type))
+ if (!same_type_ignoring_top_level_qualifiers_p (type, expr_type)
+ && ((COMPOUND_LITERAL_P (expr)
+ && CONSTRUCTOR_IS_DEPENDENT (expr)
+ && MAYBE_CLASS_TYPE_P (expr_type)
+ && TYPE_HAS_CONVERSION (expr_type))
+ /* Similarly, converting e.g. an integer to a class
+ involves a constructor call. convert_like would
+ create a TARGET_EXPR, but in a template we can't
+ use AGGR_INIT_EXPR, and the TARGET_EXPR would lead
+ to a bogus error. */
+ || (val_dep_p && MAYBE_CLASS_TYPE_P (type))))
{
expr = build1 (IMPLICIT_CONV_EXPR, type, expr);
IMPLICIT_CONV_EXPR_NONTYPE_ARG (expr) = true;
@@ -7189,8 +7197,7 @@ convert_nontype_argument (tree type, tree expr,
tsubst_flags_t complain)
/* Notice that there are constant expressions like '4 % 0' which
do not fold into integer constants. */
- if (TREE_CODE (expr) != INTEGER_CST
- && !value_dependent_expression_p (expr))
+ if (TREE_CODE (expr) != INTEGER_CST && !val_dep_p)
{
if (complain & tf_error)
{
@@ -7265,7 +7272,7 @@ convert_nontype_argument (tree type, tree expr,
tsubst_flags_t complain)
Here, we do not care about functions, as they are invalid anyway
for a parameter of type pointer-to-object. */
- if (value_dependent_expression_p (expr))
+ if (val_dep_p)
/* Non-type template parameters are OK. */
;
else if (cxx_dialect >= cxx11 && integer_zerop (expr))
@@ -7333,8 +7340,7 @@ convert_nontype_argument (tree type, tree expr,
tsubst_flags_t complain)
}
}
- if (TYPE_REF_OBJ_P (TREE_TYPE (expr))
- && value_dependent_expression_p (expr))
+ if (TYPE_REF_OBJ_P (TREE_TYPE (expr)) && val_dep_p)
/* OK, dependent reference. We don't want to ask whether a DECL is
itself value-dependent, since what we want here is its address. */;
else
@@ -7412,7 +7418,7 @@ convert_nontype_argument (tree type, tree expr,
tsubst_flags_t complain)
/* [temp.arg.nontype] bullet 1 says the pointer to member
expression must be a pointer-to-member constant. */
- if (!value_dependent_expression_p (expr)
+ if (!val_dep_p
&& !check_valid_ptrmem_cst_expr (type, expr, complain))
return NULL_TREE;
@@ -7429,7 +7435,7 @@ convert_nontype_argument (tree type, tree expr,
tsubst_flags_t complain)
{
/* [temp.arg.nontype] bullet 1 says the pointer to member
expression must be a pointer-to-member constant. */
- if (!value_dependent_expression_p (expr)
+ if (!val_dep_p
&& !check_valid_ptrmem_cst_expr (type, expr, complain))
return NULL_TREE;
@@ -7452,7 +7458,7 @@ convert_nontype_argument (tree type, tree expr,
tsubst_flags_t complain)
{
/* Replace the argument with a reference to the corresponding template
parameter object. */
- if (!value_dependent_expression_p (expr))
+ if (!val_dep_p)
expr = get_template_parm_object (expr, complain);
if (expr == error_mark_node)
return NULL_TREE;
@@ -16406,7 +16412,9 @@ tsubst_copy (tree t, tree args, tsubst_flags_t
complain, tree in_decl)
}
else
{
- gcc_assert (CP_TYPE_CONST_P (TREE_TYPE (op)));
+ gcc_assert (CP_TYPE_CONST_P (TREE_TYPE (op))
+ || (TREE_CODE (op) == IMPLICIT_CONV_EXPR
+ && IMPLICIT_CONV_EXPR_NONTYPE_ARG (op)));
return op;
}
}
diff --git a/gcc/testsuite/g++.dg/cpp2a/nontype-class28.C
b/gcc/testsuite/g++.dg/cpp2a/nontype-class28.C
new file mode 100644
index 00000000000..80b9b499355
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/nontype-class28.C
@@ -0,0 +1,37 @@
+// PR c++/92948 - Fix class NTTP with template arguments.
+// { dg-do compile { target c++2a } }
+
+struct A {
+ constexpr A(int) { }
+};
+
+template<A>
+struct B {
+ using U = unsigned;
+};
+
+template<A a>
+using U = B<a>;
+
+template<int X, typename Y = typename B<X>::U>
+void foo()
+{
+}
+
+template<int X, typename Y = typename U<X>::U>
+void foo2()
+{
+}
+
+template<typename Y = typename B<1>::U>
+void foo3()
+{
+}
+
+void
+g ()
+{
+ foo<1>();
+ foo2<1>();
+ foo3<>();
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/nontype-class29.C
b/gcc/testsuite/g++.dg/cpp2a/nontype-class29.C
new file mode 100644
index 00000000000..2d2e9690a06
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/nontype-class29.C
@@ -0,0 +1,26 @@
+// PR c++/92948 - Fix class NTTP with template arguments.
+// { dg-do run { target c++2a } }
+
+struct A {
+ int i;
+ constexpr A(int n) : i(n) { }
+};
+
+template<A a>
+struct B {
+ static constexpr int i = a.i;
+};
+
+template<int X>
+void foo()
+{
+ B<X> b;
+ if (b.i != 42)
+ __builtin_abort ();
+}
+
+int
+main ()
+{
+ foo<42>();
+}
base-commit: ad690d79cfbb905c5546c9333c5fd089d906505b
--
Marek Polacek • Red Hat, Inc. • 300 A St, Boston, MA
