[PATCH] c++: Fix ICE with { } as template argument [PR94592]

[Marek Polacek]

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.

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

	PR c++/94592
	* constexpr.c (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                           |  2 --
 gcc/testsuite/g++.dg/cpp2a/nontype-class34.C | 16 ++++++++++++++++
 gcc/testsuite/g++.dg/cpp2a/nontype-class35.C | 17 +++++++++++++++++
 3 files changed, 33 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..21a5bbd798c 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -8295,7 +8295,6 @@ 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 +8306,6 @@ 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: a28edad3da5c59f09565d3d42e20be1a924986c4
-- 
Marek Polacek • Red Hat, Inc. • 300 A St, Boston, MA