From: Martin Uecker <muecker@gwdg.de>
Date: Wed, 16 Dec 2020 22:43:42 +0000 (+0100)
Subject: C: Avoid incorrect warning for volatile in compound expressions [PR98260]
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=ec13758ed41936bf803640f0dd8c259c034fe4b9;p=gcc.git

C: Avoid incorrect warning for volatile in compound expressions [PR98260]

2020-12-16  Martin Uecker  <muecker@gwdg.de>

gcc/c/
	PR c/98260
	* c-parser.c (c_parser_expression): Look into
	nop expression when marking expressions as read.

gcc/testsuite/
	PR c/98260
	* gcc.dg/unused-9.c: New test.
---

diff --git a/gcc/c/c-parser.c b/gcc/c/c-parser.c
index 69ecdb5e822..b9fdc90274e 100644
--- a/gcc/c/c-parser.c
+++ b/gcc/c/c-parser.c
@@ -10615,8 +10615,14 @@ c_parser_expression (c_parser *parser)
       c_parser_consume_token (parser);
       expr_loc = c_parser_peek_token (parser)->location;
       lhsval = expr.value;
-      while (TREE_CODE (lhsval) == COMPOUND_EXPR)
-	lhsval = TREE_OPERAND (lhsval, 1);
+      while (TREE_CODE (lhsval) == COMPOUND_EXPR
+	     || TREE_CODE (lhsval) == NOP_EXPR)
+	{
+	  if (TREE_CODE (lhsval) == COMPOUND_EXPR)
+	    lhsval = TREE_OPERAND (lhsval, 1);
+	  else
+	    lhsval = TREE_OPERAND (lhsval, 0);
+	}
       if (DECL_P (lhsval) || handled_component_p (lhsval))
 	mark_exp_read (lhsval);
       next = c_parser_expr_no_commas (parser, NULL);
diff --git a/gcc/testsuite/gcc.dg/unused-9.c b/gcc/testsuite/gcc.dg/unused-9.c
new file mode 100644
index 00000000000..bdf36e1f50e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/unused-9.c
@@ -0,0 +1,13 @@
+/* PR c/98260 */
+/* { dg-do compile } */
+/* { dg-options "-Wunused" } */
+
+
+void g(void)
+{
+  int i = 0;
+  volatile int x;
+  (x, i++);	/* { dg-bogus "set but not used" } */
+}
+
+