Fix #52283 error: case label does not reduce to an integer constant

From-SVN: r186586

gcc/ChangeLog

+2012-04-19   Manuel López-Ibáñez  <manu@gcc.gnu.org>
+
+	PR c/52283/37985
+	* stmt.c (warn_if_unused_value): Skip NOP_EXPR.
+	* convert.c (convert_to_integer): Don't set TREE_NO_WARNING.
+
 2012-04-19  Richard Guenther  <rguenther@suse.de>
 
 	PR rtl-optimization/44688

gcc/c-family/c-common.c

@@ -1692,6 +1692,7 @@ warn_if_unused_value (const_tree exp, location_t locus)
 
     case SAVE_EXPR:
     case NON_LVALUE_EXPR:
+    case NOP_EXPR:
       exp = TREE_OPERAND (exp, 0);
       goto restart;
 

gcc/convert.c

@@ -537,7 +537,6 @@ convert_to_integer (tree type, tree expr)
       else if (outprec >= inprec)
 	{
 	  enum tree_code code;
-	  tree tem;
 
 	  /* If the precision of the EXPR's type is K bits and the
 	     destination mode has more bits, and the sign is changing,
@@ -555,13 +554,7 @@ convert_to_integer (tree type, tree expr)
 	  else
 	    code = NOP_EXPR;
 
-	  tem = fold_unary (code, type, expr);
-	  if (tem)
-	    return tem;
-
-	  tem = build1 (code, type, expr);
-	  TREE_NO_WARNING (tem) = 1;
-	  return tem;
+	  return fold_build1 (code, type, expr);
 	}
 
       /* If TYPE is an enumeral type or a type with a precision less

gcc/testsuite/ChangeLog

+2012-04-19  Christian Bruel  <christian.bruel@st.com>
+
+	* gcc.dg/pr52283.c: New test.
+
+2012-04-19   Manuel López-Ibáñez  <manu@gcc.gnu.org>
+
+	* gcc.dg/pr37985.c: New test.
+
 2012-04-19  Richard Guenther  <rguenther@suse.de>
 
 	PR rtl-optimization/44688

gcc/testsuite/gcc.dg/pr37985.c

+/* PR c37985 */
+/* { dg-do compile } */
+/* { dg-options " -Wall -Wextra " } */
+unsigned char foo(unsigned char a)
+{
+  a >> 2; /* { dg-warning "no effect" } */
+  return a;
+}

gcc/testsuite/gcc.dg/pr52283.c

+/* Test for case labels not integer constant expressions but folding
+   to integer constants (used in Linux kernel).  */
+/* { dg-do compile } */
+
+extern unsigned int u;
+
+void
+b (int c)
+{
+  switch (c)
+    {
+    case (int) (2  | ((4 < 8) ? 8 : u)):
+      ;
+    }
+}
+