re PR c++/79746 (Confusing -Wunused-but-set-parameter warning with virtual inheritance)

	PR c++/79746
	* init.c (emit_mem_initializers): When not constructing vbases of
	abstract classes, mark arguments as read for
	-Wunused-but-set-parameter.

	* g++.dg/warn/Wunused-parm-9.C: New test.

From-SVN: r245802

gcc/cp/ChangeLog

+2017-03-01  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/79746
+	* init.c (emit_mem_initializers): When not constructing vbases of
+	abstract classes, mark arguments as read for
+	-Wunused-but-set-parameter.
+
 2017-02-28  Jason Merrill  <jason@redhat.com>
 
 	Class template argument deduction refinements

gcc/cp/init.c

@@ -1217,6 +1217,12 @@ emit_mem_initializers (tree mem_inits)
 	/* C++14 DR1658 Means we do not have to construct vbases of
 	   abstract classes.  */
 	construct_virtual_base (subobject, arguments);
+      else
+	/* When not constructing vbases of abstract classes, at least mark
+	   the arguments expressions as read to avoid
+	   -Wunused-but-set-parameter false positives.  */
+	for (tree arg = arguments; arg; arg = TREE_CHAIN (arg))
+	  mark_exp_read (TREE_VALUE (arg));
 
       if (inherited_base)
 	pop_deferring_access_checks ();

gcc/testsuite/ChangeLog

 2017-03-01  Jakub Jelinek  <jakub@redhat.com>
 
+	PR c++/79746
+	* g++.dg/warn/Wunused-parm-9.C: New test.
+
 	PR tree-optimization/79734
 	* g++.dg/opt/pr79734.C: New test.
 

gcc/testsuite/g++.dg/warn/Wunused-parm-9.C

+// PR c++/79746
+// { dg-do compile }
+// { dg-options "-Wunused-but-set-parameter" }
+
+struct A {
+  A (const char *x) : a(x) {}	// { dg-bogus "set but not used" }
+  virtual int foo () = 0;
+  const char *a;
+};
+struct B : public virtual A {
+  B (const char *x) : A(x) {}	// { dg-bogus "set but not used" }
+};