From c806314b32987096d79de21e72dc0cf783e51d57 Mon Sep 17 00:00:00 2001
From: Marek Polacek <polacek@redhat.com>
Date: Fri, 22 Jan 2021 12:50:53 -0500
Subject: [PATCH] c++: Crash when deducing template arguments [PR98790]

maybe_instantiate_noexcept doesn't expect to see error_mark_node, but
the new callsite I introduced in r11-6476 can pass error_mark_node to
it.  So cope.

gcc/cp/ChangeLog:

	PR c++/98790
	* pt.c (maybe_instantiate_noexcept): Return false if FN is
	error_mark_node.

gcc/testsuite/ChangeLog:

	PR c++/98790
	* g++.dg/template/deduce8.C: New test.
---
 gcc/cp/pt.c                             |  3 +++
 gcc/testsuite/g++.dg/template/deduce8.C | 21 +++++++++++++++++++++
 2 files changed, 24 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/template/deduce8.C

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index dc2e032d6dde..abef0cdc6638 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -25323,6 +25323,9 @@ maybe_instantiate_noexcept (tree fn, tsubst_flags_t complain)
 {
   tree fntype, spec, noex, clone;
 
+  if (fn == error_mark_node)
+    return false;
+
   /* Don't instantiate a noexcept-specification from template context.  */
   if (processing_template_decl
       && (!flag_noexcept_type || type_dependent_expression_p (fn)))
diff --git a/gcc/testsuite/g++.dg/template/deduce8.C b/gcc/testsuite/g++.dg/template/deduce8.C
new file mode 100644
index 000000000000..430be4266892
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/deduce8.C
@@ -0,0 +1,21 @@
+// PR c++/98659
+// { dg-do compile }
+
+template <bool> struct enable_if;
+struct function {
+  template <typename _F> void operator=(_F);
+};
+struct map {
+  function operator[](int);
+};
+enum { E };
+template <typename> void foo ();
+template <typename T>
+typename enable_if<T::value>::type foo ();
+
+void
+bar ()
+{
+  map m;
+  m[E] = foo<int>;
+}
-- 
2.47.2