Index: gcc/c-family/c-common.c
===================================================================
--- gcc/c-family/c-common.c	(revision 240437)
+++ gcc/c-family/c-common.c	(working copy)
@@ -4651,6 +4651,19 @@ c_common_truthvalue_conversion (location_t locatio
 	return c_common_truthvalue_conversion (location,
 					       TREE_OPERAND (expr, 0));
 
+    case LSHIFT_EXPR:
+      /* Warn on signed integer left shift, except 0 << 0, 1 << 0.  */
+      if (TREE_CODE (TREE_TYPE (expr)) == INTEGER_TYPE
+	  && !TYPE_UNSIGNED (TREE_TYPE (expr))
+	  && !(TREE_CODE (TREE_OPERAND (expr, 0)) == INTEGER_CST
+	       && TREE_CODE (TREE_OPERAND (expr, 1)) == INTEGER_CST
+	       && (integer_zerop (TREE_OPERAND (expr, 0))
+		   || integer_onep (TREE_OPERAND (expr, 0)))
+	       && integer_zerop (TREE_OPERAND (expr, 1))))
+	warning_at (EXPR_LOCATION (expr), OPT_Wint_in_bool_context,
+		    "<< on signed integer in boolean context");
+      break;
+
     case COND_EXPR:
       if (warn_int_in_bool_context
 	  && !from_macro_definition_at (EXPR_LOCATION (expr)))
Index: gcc/cp/parser.c
===================================================================
--- gcc/cp/parser.c	(revision 240437)
+++ gcc/cp/parser.c	(working copy)
@@ -11172,7 +11172,7 @@ cp_parser_condition (cp_parser* parser)
 	{
 	  tree pushed_scope;
 	  bool non_constant_p;
-	  bool flags = LOOKUP_ONLYCONVERTING;
+	  int flags = LOOKUP_ONLYCONVERTING;
 
 	  /* Create the declaration.  */
 	  decl = start_decl (declarator, &type_specifiers,
Index: gcc/doc/invoke.texi
===================================================================
--- gcc/doc/invoke.texi	(revision 240437)
+++ gcc/doc/invoke.texi	(working copy)
@@ -5927,7 +5927,8 @@ of the C++ standard.
 @opindex Wno-int-in-bool-context
 Warn for suspicious use of integer values where boolean values are expected,
 such as conditional expressions (?:) using non-boolean integer constants in
-boolean context, like @code{if (a <= b ? 2 : 3)}.
+boolean context, like @code{if (a <= b ? 2 : 3)}.  Or left shifting of a
+signed integer in boolean context, like @code{for (a = 0; 1 << a; a++);}.
 This warning is enabled by @option{-Wall}.
 
 @item -Wno-int-to-pointer-cast
Index: gcc/testsuite/c-c++-common/Wint-in-bool-context.c
===================================================================
--- gcc/testsuite/c-c++-common/Wint-in-bool-context.c	(revision 240437)
+++ gcc/testsuite/c-c++-common/Wint-in-bool-context.c	(working copy)
@@ -25,5 +25,7 @@ int foo (int a, int b)
   if (b ? 1+1 : 1) /* { dg-warning "boolean context" } */
     return 7;
 
+  for (a = 0; 1 << a; a++); /* { dg-warning "boolean context" } */
+
   return 0;
 }