C++: Fix ICE in fold_for_warn on CAST_EXPR (PR c++/83974)

gcc/cp/ChangeLog:
	PR c++/83974
	* pt.c (tsubst_copy_and_build) <CONSTRUCTOR>: Remove early bailout
	for pointer to member function types.

gcc/testsuite/ChangeLog:
	PR c++/83974
	* g++.dg/warn/pr83974.C: New test case.

From-SVN: r256999

gcc/cp/ChangeLog

+2018-01-23  David Malcolm  <dmalcolm@redhat.com>
+
+	PR c++/83974
+	* pt.c (tsubst_copy_and_build) <CONSTRUCTOR>: Remove early bailout
+	for pointer to member function types.
+
 2018-01-23  Jakub Jelinek  <jakub@redhat.com>
 
 	PR sanitizer/83987

gcc/cp/pt.c

@@ -18097,10 +18097,6 @@ tsubst_copy_and_build (tree t,
 	if (type == error_mark_node)
 	  RETURN (error_mark_node);
 
-	/* digest_init will do the wrong thing if we let it.  */
-	if (type && TYPE_PTRMEMFUNC_P (type))
-	  RETURN (t);
-
 	/* We do not want to process the index of aggregate
 	   initializers as they are identifier nodes which will be
 	   looked up by digest_init.  */

gcc/testsuite/ChangeLog

+2018-01-23  David Malcolm  <dmalcolm@redhat.com>
+
+	PR c++/83974
+	* g++.dg/warn/pr83974.C: New test case.
+
 2018-01-23  Jakub Jelinek  <jakub@redhat.com>
 
 	PR sanitizer/83987

gcc/testsuite/g++.dg/warn/pr83974.C

+// { dg-options "-Wtautological-compare" }
+
+struct A {
+  typedef void (A::*B) ();
+  operator B ();
+};
+template <typename>
+struct C {
+  void foo () { d == 0; }
+  A d;
+};