c-common.c (c_common_truthvalue_conversion): Warn only for signed integer shift…

c-common.c (c_common_truthvalue_conversion): Warn only for signed integer shift ops in boolean context.

2016-10-19  Bernd Edlinger  <bernd.edlinger@hotmail.de>

        * c-common.c (c_common_truthvalue_conversion): Warn only for signed
        integer shift ops in boolean context.

testsuite:
2016-10-19  Bernd Edlinger  <bernd.edlinger@hotmail.de>

        * c-c++-common/Wint-in-bool-context-2.c: New test.

From-SVN: r241354

gcc/c-family/ChangeLog

-2016-06-16  Aldy Hernandez  <aldyh@redhat.com>
+2016-10-19  Bernd Edlinger  <bernd.edlinger@hotmail.de>
+
+	* c-common.c (c_common_truthvalue_conversion): Warn only for signed
+	integer shift ops in boolean context.
+
+2016-10-18  Aldy Hernandez  <aldyh@redhat.com>
 
 	* c.opt (Walloca): New.
 	(Walloca-larger-than=): New.

gcc/c-family/c-common.c

@@ -3328,8 +3328,15 @@ c_common_truthvalue_conversion (location_t location, tree expr)
 					       TREE_OPERAND (expr, 0));
 
     case LSHIFT_EXPR:
-      warning_at (EXPR_LOCATION (expr), OPT_Wint_in_bool_context,
-		  "<< in boolean context, did you mean '<' ?");
+      /* We will only warn on unsigned shifts here, because the majority of
+	 false positive warnings happen in code where unsigned arithmetic
+	 was used in anticipation of a possible overflow.
+	 Furthermore, if we see an unsigned type here we know that the
+	 result of the shift is not subject to integer promotion rules.  */
+      if (TREE_CODE (TREE_TYPE (expr)) == INTEGER_TYPE
+	  && !TYPE_UNSIGNED (TREE_TYPE (expr)))
+	warning_at (EXPR_LOCATION (expr), OPT_Wint_in_bool_context,
+		    "<< in boolean context, did you mean '<' ?");
       break;
 
     case COND_EXPR:

gcc/testsuite/ChangeLog

+2016-10-19  Bernd Edlinger  <bernd.edlinger@hotmail.de>
+
+	* c-c++-common/Wint-in-bool-context-2.c: New test.
+
 2016-10-19  Jerry DeLisle  <jvdelisle@gcc.gnu.org>
 
 	* gfortran.dg/dtio_17.f90: Fix test.

gcc/testsuite/c-c++-common/Wint-in-bool-context-2.c

+/* { dg-options "-Wint-in-bool-context" } */
+/* { dg-do compile } */
+
+typedef unsigned u32;
+typedef unsigned char u8;
+#define KEYLENGTH 8
+
+int foo (u8 plen, u32 key)
+{
+  if ((plen < KEYLENGTH) && (key << plen)) /* { dg-bogus "boolean context" } */
+    return -1;
+
+  if ((plen << KEYLENGTH) && (key < plen)) /* { dg-warning "boolean context" } */
+    return -2;
+
+  return 0;
+}