c++: ICE with constexpr variable template [PR107938]

Since r11-557, cp_finish_decl can call check_initializer even in
a template for a constexpr initializer.  That ultimately leads to
convert_for_assignment and check_address_or_pointer_of_packed_member,
where we crash, because it doesn't expect that the CALL_EXPR is
a function object.  Q has a constexpr operator(), but since we're
in a template, q(0) is a CALL_EXPR whose CALL_EXPR_FN is just
a VAR_DECL; it hasn't been converted to Q::operator<int>(&q, 0) yet.
I propose to robustify check_address_or_pointer_of_packed_member.

var-templ74.C has an XFAIL, subject to 107939.

I noticed that our -Waddress-of-packed-member tests weren't testing
member functions, added thus.  (I was tempted to check
FUNCTION_POINTER_TYPE_P but that doesn't include METHOD_TYPE.)

	PR c++/107938

gcc/c-family/ChangeLog:

	* c-warn.cc (check_address_or_pointer_of_packed_member): Check
	POINTER_TYPE_P.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp1y/var-templ73.C: New test.
	* g++.dg/cpp1y/var-templ74.C: New test.
	* g++.dg/warn/Waddress-of-packed-member3.C: New test.

4 files changed, 58 insertions, 0 deletions

diff --git a/gcc/c-family/c-warn.cc b/gcc/c-family/c-warn.cc
index a6fb95b..29ae1ea 100644
--- a/gcc/c-family/c-warn.cc
+++ b/gcc/c-family/c-warn.cc
@@ -3000,6 +3000,10 @@ check_address_or_pointer_of_packed_member (tree type, tree rhs)
 	  if (rhs == NULL_TREE)
 	    return NULL_TREE;
 	  rhs = TREE_TYPE (rhs);	/* Pointer type.  */
+	  /* We could be called while processing a template and RHS could be
+	     a functor.  In that case it's a class, not a pointer.  */
+	  if (!POINTER_TYPE_P (rhs))
+	    return NULL_TREE;
 	  rhs = TREE_TYPE (rhs);	/* Function type.  */
 	  rhstype = TREE_TYPE (rhs);
 	  if (!rhstype || !POINTER_TYPE_P (rhstype))
diff --git a/gcc/testsuite/g++.dg/cpp1y/var-templ73.C b/gcc/testsuite/g++.dg/cpp1y/var-templ73.C
new file mode 100644
index 0000000..b76babc
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/var-templ73.C
@@ -0,0 +1,12 @@
+// PR c++/107938
+// { dg-do compile { target c++14 } }
+
+struct Q {
+  int n;
+  constexpr const Q* operator()(int) const { return this; }
+};
+
+constexpr Q q{};
+
+template<int>
+constexpr const Q* p = q(0);
diff --git a/gcc/testsuite/g++.dg/cpp1y/var-templ74.C b/gcc/testsuite/g++.dg/cpp1y/var-templ74.C
new file mode 100644
index 0000000..4e2e800
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/var-templ74.C
@@ -0,0 +1,19 @@
+// PR c++/107938
+// { dg-do compile { target c++14 } }
+
+struct Q {
+  int n;
+  constexpr const Q* operator()(int) const { return this; }
+};
+
+extern const Q q;
+
+template<int>
+constexpr const Q* p = q(0); // { dg-bogus "not usable" "PR107939" { xfail *-*-* } }
+
+void
+g ()
+{
+  constexpr const Q* p2 = q(0);
+  constexpr auto x = p<0>;
+}
diff --git a/gcc/testsuite/g++.dg/warn/Waddress-of-packed-member3.C b/gcc/testsuite/g++.dg/warn/Waddress-of-packed-member3.C
new file mode 100644
index 0000000..aeffb96
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Waddress-of-packed-member3.C
@@ -0,0 +1,23 @@
+// { dg-do compile { target { ! default_packed } } }
+// Test that -Waddress-of-packed-member works with member functions.
+
+struct S {
+  char c;
+} __attribute__((packed));
+
+struct X {
+  S* memfn ();
+  static S* smemfn ();
+} x;
+
+S *foo ();
+
+S**
+f ()
+{
+  S **s;
+  s = reinterpret_cast<S**>(foo ()); // { dg-warning "converting a packed" }
+  s = reinterpret_cast<S**>(x.memfn ()); // { dg-warning "converting a packed" }
+  s = reinterpret_cast<S**>(X::smemfn ()); // { dg-warning "converting a packed" }
+  return s;
+}