On Mon, Apr 20, 2020 at 11:51:59AM -0400, Jason Merrill wrote:
> On 4/17/20 4:28 PM, Marek Polacek wrote:
> > As an extension (there should be a CWG about this though), we support
> > braced-init-list as a template argument, but convert_nontype_argument
> > had trouble digesting them. We ICEd because of the double coercion we
> > perform for template arguments: convert_nontype_argument called from
> > finish_template_type got a { }, and since a class type was involved and
> > we were in a template, convert_like created an IMPLICIT_CONV_EXPR. Then
> > the second conversion of the same argument crashed in constexpr.c
> > because the IMPLICIT_CONV_EXPR had gotten wrapped in a TARGET_EXPR.
> > Another issue was that an IMPLICIT_CONV_EXPR leaked to constexpr.c when
> > building an aggregate init.
> >
> > We should have instantiated the IMPLICIT_CONV_EXPR in the first call to
> > convert_nontype_argument, but we didn't, because the call to
> > is_nondependent_constant_expression returned false because it checks
> > !BRACE_ENCLOSED_INITIALIZER_P. Then non_dep was false even though the
> > expression didn't contain anything dependent and we didn't instantiate
> > it in convert_nontype_argument. I'm not sure what the point
> > of that BRACE_ENCLOSED_INITIALIZER_P. check was, but removing it doesn't
> > break anything and fixes these crashes.
>
> The point was to avoid trying to get a constant value for an untyped
> braced-init-list. I'm happy to remove the check from these functions, but
> let's add it back to maybe_constant_{value,init}, where it was until
> r6-7825-geb07f187a471f9a203626aecced17d6947c3cc46 .
Thanks for the pointer.
> Or better, put it in cxx_eval_outermost_constant_expr.
Done here. Since we didn't set non_constant_p and emit an error, I'm not
doing it here, either.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
-- >8 --
As an extension (there should be a CWG about this though), we support
braced-init-list as a template argument, but convert_nontype_argument
had trouble digesting them. We ICEd because of the double coercion we
perform for template arguments: convert_nontype_argument called from
finish_template_type got a { }, and since a class type was involved and
we were in a template, convert_like created an IMPLICIT_CONV_EXPR. Then
the second conversion of the same argument crashed in constexpr.c
because the IMPLICIT_CONV_EXPR had gotten wrapped in a TARGET_EXPR.
Another issue was that an IMPLICIT_CONV_EXPR leaked to constexpr.c when
building an aggregate init.
We should have instantiated the IMPLICIT_CONV_EXPR in the first call to
convert_nontype_argument, but we didn't, because the call to
is_nondependent_constant_expression returned false because it checks
!BRACE_ENCLOSED_INITIALIZER_P. Then non_dep was false even though the
expression didn't contain anything dependent and we didn't instantiate
it in convert_nontype_argument. To fix this, check
BRACE_ENCLOSED_INITIALIZER_P in cxx_eval_outermost_constant_expr rather
than in is_nondependent_*.
PR c++/94592
* constexpr.c (cxx_eval_outermost_constant_expr): Return when T is
a BRACE_ENCLOSED_INITIALIZER_P.
(is_nondependent_constant_expression): Don't check
BRACE_ENCLOSED_INITIALIZER_P.
(is_nondependent_static_init_expression): Likewise.
* g++.dg/cpp2a/nontype-class34.C: New test.
* g++.dg/cpp2a/nontype-class35.C: New test.
---
gcc/cp/constexpr.c | 5 +++--
gcc/testsuite/g++.dg/cpp2a/nontype-class34.C | 16 ++++++++++++++++
gcc/testsuite/g++.dg/cpp2a/nontype-class35.C | 17 +++++++++++++++++
3 files changed, 36 insertions(+), 2 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/nontype-class34.C
create mode 100644 gcc/testsuite/g++.dg/cpp2a/nontype-class35.C
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index c8e7d083f40..fa592834f0a 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -6534,6 +6534,9 @@ cxx_eval_outermost_constant_expr (tree t, bool
allow_non_constant,
bool non_constant_p = false;
bool overflow_p = false;
+ if (BRACE_ENCLOSED_INITIALIZER_P (t))
+ return t;
+
constexpr_global_ctx global_ctx;
constexpr_ctx ctx = { &global_ctx, NULL, NULL, NULL, NULL, NULL, NULL,
allow_non_constant, strict,
@@ -8295,7 +8298,6 @@ bool
is_nondependent_constant_expression (tree t)
{
return (!type_unknown_p (t)
- && !BRACE_ENCLOSED_INITIALIZER_P (t)
&& is_constant_expression (t)
&& !instantiation_dependent_expression_p (t));
}
@@ -8307,7 +8309,6 @@ bool
is_nondependent_static_init_expression (tree t)
{
return (!type_unknown_p (t)
- && !BRACE_ENCLOSED_INITIALIZER_P (t)
&& is_static_init_expression (t)
&& !instantiation_dependent_expression_p (t));
}
diff --git a/gcc/testsuite/g++.dg/cpp2a/nontype-class34.C
b/gcc/testsuite/g++.dg/cpp2a/nontype-class34.C
new file mode 100644
index 00000000000..2d3ba018618
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/nontype-class34.C
@@ -0,0 +1,16 @@
+// PR c++/94592 - ICE with { } as template argument.
+// { dg-do compile { target c++2a } }
+
+struct A {
+ constexpr A() {}
+};
+
+template <A> struct B { };
+
+template<typename> void bar () {
+ B<{}> var;
+}
+
+void fu() {
+ bar<int>();
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/nontype-class35.C
b/gcc/testsuite/g++.dg/cpp2a/nontype-class35.C
new file mode 100644
index 00000000000..78cf0a39c81
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/nontype-class35.C
@@ -0,0 +1,17 @@
+// PR c++/94592 - ICE with { } as template argument.
+// { dg-do compile { target c++2a } }
+
+struct A {
+ int i;
+ constexpr A(int n) : i(n) {}
+};
+
+template <A a> struct B { int i; constexpr B() : i(a.i) { } };
+
+template<typename> void bar () {
+ B<{1}> var;
+}
+
+void fu() {
+ bar<int>();
+}
base-commit: 5bdd4c5d3fc9c143e8edea3b10828e4b75d7a385
--
Marek Polacek • Red Hat, Inc. • 300 A St, Boston, MA
