c++: more ahead-of-time -Wparentheses warnings

Now that we don't have to worry about looking through NON_DEPENDENT_EXPR,
we can easily extend the -Wparentheses warning in convert_for_assignment
to consider (non-dependent) templated assignment operator expressions as
well, like r14-4111-g6e92a6a2a72d3b did in maybe_convert_cond.

gcc/cp/ChangeLog:

	* cp-tree.h (maybe_warn_unparenthesized_assignment): Declare.
	* semantics.cc (is_assignment_op_expr_p): Generalize to return
	true for any assignment operator expression, not just one that
	has been resolved to an operator overload.
	(maybe_warn_unparenthesized_assignment): Factored out from ...
	(maybe_convert_cond): ... here.
	(finish_parenthesized_expr): Mention
	maybe_warn_unparenthesized_assignment.
	* typeck.cc (convert_for_assignment): Replace -Wparentheses
	warning logic with maybe_warn_unparenthesized_assignment.

gcc/testsuite/ChangeLog:

	* g++.dg/warn/Wparentheses-13.C: Strengthen by expecting that
	we issue the -Wparentheses warnings ahead of time.
	* g++.dg/warn/Wparentheses-23.C: Likewise.
	* g++.dg/warn/Wparentheses-32.C: Remove xfails.

6 files changed, 44 insertions, 38 deletions

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 30fe716..98b29e9 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -7875,6 +7875,7 @@ extern tree lambda_regenerating_args		(tree);
 extern tree most_general_lambda			(tree);
 extern tree finish_omp_target			(location_t, tree, tree, bool);
 extern void finish_omp_target_clauses		(location_t, tree, tree *);
+extern void maybe_warn_unparenthesized_assignment (tree, tsubst_flags_t);
 
 /* in tree.cc */
 extern int cp_tree_operand_length		(const_tree);
diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index 72ec72d..52044be 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -840,15 +840,20 @@ finish_goto_stmt (tree destination)
   return add_stmt (build_stmt (input_location, GOTO_EXPR, destination));
 }
 
-/* Returns true if CALL is a (possibly wrapped) CALL_EXPR or AGGR_INIT_EXPR
-   to operator= () that is written as an operator expression. */
+/* Returns true if T corresponds to an assignment operator expression.  */
+
 static bool
-is_assignment_op_expr_p (tree call)
+is_assignment_op_expr_p (tree t)
 {
-  if (call == NULL_TREE)
+  if (t == NULL_TREE)
     return false;
 
-  call = extract_call_expr (call);
+  if (TREE_CODE (t) == MODIFY_EXPR
+      || (TREE_CODE (t) == MODOP_EXPR
+	  && TREE_CODE (TREE_OPERAND (t, 1)) == NOP_EXPR))
+    return true;
+
+  tree call = extract_call_expr (t);
   if (call == NULL_TREE
       || call == error_mark_node
       || !CALL_EXPR_OPERATOR_SYNTAX (call))
@@ -860,6 +865,28 @@ is_assignment_op_expr_p (tree call)
     && DECL_OVERLOADED_OPERATOR_IS (fndecl, NOP_EXPR);
 }
 
+/* Maybe warn about an unparenthesized 'a = b' (appearing in a
+   boolean context where 'a == b' might have been intended).  */
+
+void
+maybe_warn_unparenthesized_assignment (tree t, tsubst_flags_t complain)
+{
+  if (REFERENCE_REF_P (t))
+    t = TREE_OPERAND (t, 0);
+
+  if ((complain & tf_warning)
+      && warn_parentheses
+      && is_assignment_op_expr_p (t)
+      /* A parenthesized expression would've had this warning
+	 suppressed by finish_parenthesized_expr.  */
+      && !warning_suppressed_p (t, OPT_Wparentheses))
+    {
+      warning_at (cp_expr_loc_or_input_loc (t), OPT_Wparentheses,
+		  "suggest parentheses around assignment used as truth value");
+      suppress_warning (t, OPT_Wparentheses);
+    }
+}
+
 /* COND is the condition-expression for an if, while, etc.,
    statement.  Convert it to a boolean value, if appropriate.
    In addition, verify sequence points if -Wsequence-point is enabled.  */
@@ -878,21 +905,10 @@ maybe_convert_cond (tree cond)
   if (warn_sequence_point && !processing_template_decl)
     verify_sequence_points (cond);
 
+  maybe_warn_unparenthesized_assignment (cond, tf_warning_or_error);
+
   /* Do the conversion.  */
   cond = convert_from_reference (cond);
-
-  tree inner = REFERENCE_REF_P (cond) ? TREE_OPERAND (cond, 0) : cond;
-  if ((TREE_CODE (inner) == MODIFY_EXPR
-       || (TREE_CODE (inner) == MODOP_EXPR
-	   && TREE_CODE (TREE_OPERAND (inner, 1)) == NOP_EXPR)
-       || is_assignment_op_expr_p (inner))
-      && warn_parentheses
-      && !warning_suppressed_p (inner, OPT_Wparentheses)
-      && warning_at (cp_expr_loc_or_input_loc (inner),
-		     OPT_Wparentheses, "suggest parentheses around "
-				       "assignment used as truth value"))
-    suppress_warning (inner, OPT_Wparentheses);
-
   return condition_conversion (cond);
 }
 
@@ -2158,7 +2174,8 @@ finish_parenthesized_expr (cp_expr expr)
 {
   if (EXPR_P (expr))
     {
-      /* This inhibits warnings in c_common_truthvalue_conversion.  */
+      /* This inhibits warnings in maybe_warn_unparenthesized_assignment
+	 and c_common_truthvalue_conversion.  */
       tree inner = REFERENCE_REF_P (expr) ? TREE_OPERAND (expr, 0) : *expr;
       suppress_warning (inner, OPT_Wparentheses);
     }
diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
index 00570f1..49afbd8 100644
--- a/gcc/cp/typeck.cc
+++ b/gcc/cp/typeck.cc
@@ -10338,16 +10338,9 @@ convert_for_assignment (tree type, tree rhs,
 
   /* If -Wparentheses, warn about a = b = c when a has type bool and b
      does not.  */
-  if (warn_parentheses
-      && TREE_CODE (type) == BOOLEAN_TYPE
-      && TREE_CODE (rhs) == MODIFY_EXPR
-      && !warning_suppressed_p (rhs, OPT_Wparentheses)
-      && TREE_CODE (TREE_TYPE (rhs)) != BOOLEAN_TYPE
-      && (complain & tf_warning)
-      && warning_at (rhs_loc, OPT_Wparentheses,
-		     "suggest parentheses around assignment used as "
-		     "truth value"))
-    suppress_warning (rhs, OPT_Wparentheses);
+  if (TREE_CODE (type) == BOOLEAN_TYPE
+      && TREE_CODE (TREE_TYPE (rhs)) != BOOLEAN_TYPE)
+    maybe_warn_unparenthesized_assignment (rhs, complain);
 
   if (complain & tf_warning)
     warn_for_address_or_pointer_of_packed_member (type, rhs);
diff --git a/gcc/testsuite/g++.dg/warn/Wparentheses-13.C b/gcc/testsuite/g++.dg/warn/Wparentheses-13.C
index 22a139f..d643894 100644
--- a/gcc/testsuite/g++.dg/warn/Wparentheses-13.C
+++ b/gcc/testsuite/g++.dg/warn/Wparentheses-13.C
@@ -65,5 +65,3 @@ bar (T)
   d = (a = a);
   foo (27);
 }
-
-template void bar<int> (int); // { dg-message "required" }
diff --git a/gcc/testsuite/g++.dg/warn/Wparentheses-23.C b/gcc/testsuite/g++.dg/warn/Wparentheses-23.C
index f1749c2..bd7195e 100644
--- a/gcc/testsuite/g++.dg/warn/Wparentheses-23.C
+++ b/gcc/testsuite/g++.dg/warn/Wparentheses-23.C
@@ -114,8 +114,5 @@ bar4 (T)
   return (a = a);
 }
 
-template void bar<int> (int); // { dg-message "required" }
-template bool bar1<int> (int); // { dg-message "required" }
 template bool bar2<int> (int);
-template bool bar3<int> (int); // { dg-message "required" }
 template bool bar4<int> (int);
diff --git a/gcc/testsuite/g++.dg/warn/Wparentheses-32.C b/gcc/testsuite/g++.dg/warn/Wparentheses-32.C
index 719a9d9..b03515a 100644
--- a/gcc/testsuite/g++.dg/warn/Wparentheses-32.C
+++ b/gcc/testsuite/g++.dg/warn/Wparentheses-32.C
@@ -21,8 +21,8 @@ void f() {
   if (z1 = z2) { } // { dg-warning "parentheses" }
 
   bool b;
-  b = m = n; // { dg-warning "parentheses" "" { xfail *-*-* } }
-  b = x1 = x2; // { dg-warning "parentheses" "" { xfail *-*-* } }
-  b = y1 = y2; // { dg-warning "parentheses" "" { xfail *-*-* } }
-  b = z1 = z2; // { dg-warning "parentheses" "" { xfail *-*-* } }
+  b = m = n; // { dg-warning "parentheses" }
+  b = x1 = x2; // { dg-warning "parentheses" }
+  b = y1 = y2; // { dg-warning "parentheses" }
+  b = z1 = z2; // { dg-warning "parentheses" }
 }