re PR c/64637 (Incorrect location for -Wunused-value warnings in for-loop)

	PR c/64637
	* c-typeck.c (c_process_expr_stmt): Use location of the expression if
	available.

	* gcc.dg/pr64637.c: New test.

From-SVN: r231700

gcc/c/ChangeLog

+2015-12-16  Marek Polacek  <polacek@redhat.com>
+
+	PR c/64637
+	* c-typeck.c (c_process_expr_stmt): Use location of the expression if
+	available.
+
 2015-12-15  Marek Polacek  <polacek@redhat.com>
 
 	PR c/68907

gcc/c/c-typeck.c

@@ -10131,7 +10131,7 @@ c_process_expr_stmt (location_t loc, tree expr)
      out which is the result.  */
   if (!STATEMENT_LIST_STMT_EXPR (cur_stmt_list)
       && warn_unused_value)
-    emit_side_effect_warnings (loc, expr);
+    emit_side_effect_warnings (EXPR_LOC_OR_LOC (expr, loc), expr);
 
   exprv = expr;
   while (TREE_CODE (exprv) == COMPOUND_EXPR)

gcc/testsuite/ChangeLog

+2015-12-16  Marek Polacek  <polacek@redhat.com>
+
+	PR c/64637
+	* gcc.dg/pr64637.c: New test.
+
 2015-12-16  Nathan Sidwell  <nathan@acm.org>
 
 	* gcc.dg/sibcall-9.c: Xfail for nvptx.

gcc/testsuite/gcc.dg/pr64637.c

+/* PR c/64637 */
+/* { dg-do compile } */
+/* { dg-options "-Wunused" } */
+
+void g ();
+
+void
+f (int b)
+{
+  for (int i = 0; i < b; i + b) /* { dg-warning "28:statement with no effect" } */
+    g ();
+  // PARM_DECLs still don't have a location, don't expect an exact location.
+  for (int i = 0; i < b; b) /* { dg-warning "statement with no effect" } */
+    g ();
+  for (int i = 0; i < b; !i) /* { dg-warning "26:statement with no effect" } */
+    g ();
+  for (!b;;) /* { dg-warning "8:statement with no effect" } */
+    g ();
+  for (;; b * 2) /* { dg-warning "13:statement with no effect" } */
+    g ();
+  ({
+     b / 5; /* { dg-warning "8:statement with no effect" } */
+     b ^ 5;
+   });
+}