PR c++/66543 - -Wunused-but-set* false positives

	* expr.c (mark_exp_read): Handle NON_DEPENDENT_EXPR.
	* pt.c (make_pack_expansion): Call mark_exp_read.
	* semantics.c (finish_id_expression): Call mark_type_use in
	unevaluated context.

From-SVN: r235221

gcc/cp/ChangeLog

 2016-04-19  Jason Merrill  <jason@redhat.com>
 
+	PR c++/66543
+	* expr.c (mark_exp_read): Handle NON_DEPENDENT_EXPR.
+	* pt.c (make_pack_expansion): Call mark_exp_read.
+	* semantics.c (finish_id_expression): Call mark_type_use in
+	unevaluated context.
+
 	DR 2137
 	* call.c (implicit_conversion): If we choose a copy constructor
 	for list-initialization from the same type, the conversion is an

gcc/cp/expr.c

@@ -145,6 +145,7 @@ mark_exp_read (tree exp)
     case ADDR_EXPR:
     case INDIRECT_REF:
     case FLOAT_EXPR:
+    case NON_DEPENDENT_EXPR:
       mark_exp_read (TREE_OPERAND (exp, 0));
       break;
     case COMPOUND_EXPR:

gcc/cp/pt.c

@@ -3696,6 +3696,8 @@ make_pack_expansion (tree arg)
       /* Propagate type and const-expression information.  */
       TREE_TYPE (result) = TREE_TYPE (arg);
       TREE_CONSTANT (result) = TREE_CONSTANT (arg);
+      /* Mark this read now, since the expansion might be length 0.  */
+      mark_exp_read (arg);
     }
   else
     /* Just use structural equality for these TYPE_PACK_EXPANSIONS;

gcc/cp/semantics.c

@@ -3487,6 +3487,12 @@ finish_id_expression (tree id_expression,
       if (!scope && decl != error_mark_node && identifier_p (id_expression))
 	maybe_note_name_used_in_class (id_expression, decl);
 
+      /* A use in unevaluated operand might not be instantiated appropriately
+	 if tsubst_copy builds a dummy parm, or if we never instantiate a
+	 generic lambda, so mark it now.  */
+      if (processing_template_decl && cp_unevaluated_operand)
+	mark_type_use (decl);
+
       /* Disallow uses of local variables from containing functions, except
 	 within lambda-expressions.  */
       if (outer_automatic_var_p (decl))

gcc/testsuite/g++.dg/warn/Wunused-parm-7.C

+// { dg-do compile { target c++11 } }
+// { dg-options "-Wunused-but-set-parameter" }
+
+template <typename... Ts> void sink(Ts...);
+
+struct A { int i; };
+
+template <int... I>
+void f(A a)
+{
+  return sink((a.i + I)...);
+}
+
+int main()
+{
+  f<>(A());
+}

gcc/testsuite/g++.dg/warn/Wunused-parm-8.C

+// { dg-do compile { target c++14 } }
+// { dg-options "-Wunused-but-set-parameter" }
+
+auto l = [](auto t) -> decltype(true ? t : 0) { return {}; };
+
+int main()
+{
+  l(42);
+}

gcc/testsuite/g++.dg/warn/Wunused-var-24.C

+// PR c++/66543
+// { dg-do compile { target c++14 } }
+// { dg-options "-Wunused-but-set-variable" }
+
+int main() {
+  auto f = []() { };
+  [=](auto) {
+    using Foo = decltype(f());
+  };
+}

gcc/testsuite/g++.dg/warn/Wunused-var-25.C

+// { dg-do compile { target c++14 } }
+// { dg-options "-Wunused-but-set-variable" }
+
+template <int... I> struct A { };
+template <int... I>
+auto f()
+{
+  constexpr int ar[sizeof...(I)+1] = {I...};
+  return A<ar[I]...>();
+}
+
+int main()
+{
+  f<>();
+}