re PR debug/83547 ((statement-frontiers) error: void value not ignored as it ought to be)

	PR debug/83547
	* tree-iterator.c (alloc_stmt_list): Start with cleared
	TREE_SIDE_EFFECTS regardless whether a new STATEMENT_LIST is allocated
	or old one reused.
c/
	* c-typeck.c (c_finish_stmt_expr): Ignore !TREE_SIDE_EFFECTS as
	indicator of ({ }), instead skip all trailing DEBUG_BEGIN_STMTs first,
	and consider empty ones if there are no other stmts.  For
	-Wunused-value walk all statements before the one only followed by
	DEBUG_BEGIN_STMTs.
testsuite/
	* gcc.c-torture/compile/pr83547.c: New test.

From-SVN: r255980

gcc/ChangeLog

 2017-12-22  Jakub Jelinek  <jakub@redhat.com>
 
+	PR debug/83547
+	* tree-iterator.c (alloc_stmt_list): Start with cleared
+	TREE_SIDE_EFFECTS regardless whether a new STATEMENT_LIST is allocated
+	or old one reused.
+
 	PR target/83488
 	* config/i386/avx512vnniintrin.h: Don't check for __AVX512F__ nor
 	enable avx512f explicitly in #pragma GCC target.

gcc/c/ChangeLog

+2017-12-22  Jakub Jelinek  <jakub@redhat.com>
+
+	PR debug/83547
+	* c-typeck.c (c_finish_stmt_expr): Ignore !TREE_SIDE_EFFECTS as
+	indicator of ({ }), instead skip all trailing DEBUG_BEGIN_STMTs first,
+	and consider empty ones if there are no other stmts.  For
+	-Wunused-value walk all statements before the one only followed by
+	DEBUG_BEGIN_STMTs.
+
 2017-12-22  Mike Stump  <mikestump@comcast.net>
             Eric Botcazou  <ebotcazou@adacore.com>
 

gcc/c/c-typeck.c

@@ -10751,17 +10751,21 @@ c_finish_stmt_expr (location_t loc, tree body)
  continue_searching:
   if (TREE_CODE (last) == STATEMENT_LIST)
     {
-      tree_stmt_iterator i;
+      tree_stmt_iterator l = tsi_last (last);
+
+      while (!tsi_end_p (l) && TREE_CODE (tsi_stmt (l)) == DEBUG_BEGIN_STMT)
+	tsi_prev (&l);
 
       /* This can happen with degenerate cases like ({ }).  No value.  */
-      if (!TREE_SIDE_EFFECTS (last))
+      if (tsi_end_p (l))
 	return body;
 
       /* If we're supposed to generate side effects warnings, process
 	 all of the statements except the last.  */
       if (warn_unused_value)
 	{
-	  for (i = tsi_start (last); !tsi_one_before_end_p (i); tsi_next (&i))
+	  for (tree_stmt_iterator i = tsi_start (last);
+	       tsi_stmt (i) != tsi_stmt (l); tsi_next (&i))
 	    {
 	      location_t tloc;
 	      tree t = tsi_stmt (i);
@@ -10770,13 +10774,7 @@ c_finish_stmt_expr (location_t loc, tree body)
 	      emit_side_effect_warnings (tloc, t);
 	    }
 	}
-      else
-	i = tsi_last (last);
-      if (TREE_CODE (tsi_stmt (i)) == DEBUG_BEGIN_STMT)
-	do
-	  tsi_prev (&i);
-	while (TREE_CODE (tsi_stmt (i)) == DEBUG_BEGIN_STMT);
-      last_p = tsi_stmt_ptr (i);
+      last_p = tsi_stmt_ptr (l);
       last = *last_p;
     }
 

gcc/testsuite/ChangeLog

 2017-12-22  Jakub Jelinek  <jakub@redhat.com>
 
+	PR debug/83547
+	* gcc.c-torture/compile/pr83547.c: New test.
+
 	PR target/83488
 	* gcc.target/i386/pr83488-2.c: New test.
 	* gcc.target/i386/pr83488-3.c: New test.

gcc/testsuite/gcc.c-torture/compile/pr83547.c

+/* PR debug/83547 */
+
+void
+foo (void)
+{
+  if (({ 0; }))
+    ;
+  if (({ 0; 0; }))
+    ;
+  if (({ }))		/* { dg-error "void value not ignored as it ought to be" } */
+    ;
+  if (({ 0; { 0; } }))	/* { dg-error "void value not ignored as it ought to be" } */
+    ;
+  if (({ 0; {} }))	/* { dg-error "void value not ignored as it ought to be" } */
+    ;
+}

gcc/tree-iterator.c

@@ -41,7 +41,10 @@ alloc_stmt_list (void)
       TREE_SET_CODE (list, STATEMENT_LIST);
     }
   else
-    list = make_node (STATEMENT_LIST);
+    {
+      list = make_node (STATEMENT_LIST);
+      TREE_SIDE_EFFECTS (list) = 0;
+    }
   TREE_TYPE (list) = void_type_node;
   return list;
 }