Warn when comparing nonnull arguments to NULL in a function.

If an argument is marked as nonnull then passing in a NULL argument
will produce bad results even if the code checks against NULL. GCC
might optimize such checks away so warn the user when the function
contains such comparisons.

nn.c: In function ‘foo’:
nn.c:6:27: warning: nonnull argument ‘bar’ compared to NULL [-Wnonnull]
 void foo(void *bar) { if (!bar) abort(); }
                           ^
gcc/ChangeLog

	* doc/invoke.texi (Wnonnull): Also warns when comparing against NULL.

gcc/c/ChangeLog

       * c-typeck.c (build_binary_op): Check and warn when nonnull arg
       parm against NULL.

gcc/cp/ChangeLog

       * typeck.c (cp_build_binary_op): Check and warn when nonnull arg
       parm against NULL.

gcc/testsuite/ChangeLog

       * c-c++-common/nonnull-1.c: New test.

From-SVN: r227649

gcc/ChangeLog

+2015-09-09  Mark Wielaard  <mjw@redhat.com>
+
+	* doc/invoke.texi (Wnonnull): Also warns when comparing against NULL.
+
 2015-09-10  Oleg Endo  <olegendo@gcc.gnu.org>
 
 	PR target/67506

gcc/c/ChangeLog

+2015-09-09  Mark Wielaard  <mjw@redhat.com>
+
+	* c-typeck.c (build_binary_op): Check and warn when nonnull arg
+	parm against NULL.
+
 2015-09-10  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c/67502

gcc/c/c-typeck.c

@@ -10803,6 +10803,11 @@ build_binary_op (location_t location, enum tree_code code,
 	short_compare = 1;
       else if (code0 == POINTER_TYPE && null_pointer_constant_p (orig_op1))
 	{
+	  if (warn_nonnull
+	      && TREE_CODE (op0) == PARM_DECL && nonnull_arg_p (op0))
+	    warning_at (location, OPT_Wnonnull,
+			"nonnull argument %qD compared to NULL", op0);
+
 	  if (TREE_CODE (op0) == ADDR_EXPR
 	      && decl_with_nonnull_addr_p (TREE_OPERAND (op0, 0)))
 	    {
@@ -10823,6 +10828,11 @@ build_binary_op (location_t location, enum tree_code code,
 	}
       else if (code1 == POINTER_TYPE && null_pointer_constant_p (orig_op0))
 	{
+	  if (warn_nonnull
+	      && TREE_CODE (op1) == PARM_DECL && nonnull_arg_p (op1))
+	    warning_at (location, OPT_Wnonnull,
+			"nonnull argument %qD compared to NULL", op1);
+
 	  if (TREE_CODE (op1) == ADDR_EXPR
 	      && decl_with_nonnull_addr_p (TREE_OPERAND (op1, 0)))
 	    {

gcc/cp/ChangeLog

+2015-09-09  Mark Wielaard  <mjw@redhat.com>
+
+	* typeck.c (cp_build_binary_op): Check and warn when nonnull arg
+	parm against NULL.
+
 2015-09-10  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c++/67522

gcc/cp/typeck.c

@@ -4438,6 +4438,11 @@ cp_build_binary_op (location_t location,
 	       || (code0 == POINTER_TYPE
 		   && TYPE_PTR_P (type1) && integer_zerop (op1)))
 	{
+	  if (warn_nonnull
+	      && TREE_CODE (op0) == PARM_DECL && nonnull_arg_p (op0))
+	    warning_at (location, OPT_Wnonnull,
+			"nonnull argument %qD compared to NULL", op0);
+
 	  if (TYPE_PTR_P (type1))
 	    result_type = composite_pointer_type (type0, type1, op0, op1,
 						  CPO_COMPARISON, complain);
@@ -4477,6 +4482,11 @@ cp_build_binary_op (location_t location,
 	       || (code1 == POINTER_TYPE
 		   && TYPE_PTR_P (type0) && integer_zerop (op0)))
 	{
+	  if (warn_nonnull
+	      && TREE_CODE (op1) == PARM_DECL && nonnull_arg_p (op1))
+	    warning_at (location, OPT_Wnonnull,
+			"nonnull argument %qD compared to NULL", op1);
+
 	  if (TYPE_PTR_P (type0))
 	    result_type = composite_pointer_type (type0, type1, op0, op1,
 						  CPO_COMPARISON, complain);

gcc/doc/invoke.texi

@@ -3720,6 +3720,9 @@ formats that may yield only a two-digit year.
 Warn about passing a null pointer for arguments marked as
 requiring a non-null value by the @code{nonnull} function attribute.
 
+Also warns when comparing an argument marked with the @code{nonnull}
+function attribute against null inside the function.
+
 @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}.  It
 can be disabled with the @option{-Wno-nonnull} option.
 

gcc/testsuite/ChangeLog

+2015-09-09  Mark Wielaard  <mjw@redhat.com>
+
+	* c-c++-common/nonnull-1.c: New test.
+
 2015-09-10  Paul Thomas  <pault@gcc.gnu.org>
 
 	PR fortran/66993

gcc/testsuite/c-c++-common/nonnull-1.c

+/* Test for the bad usage of "nonnull" function attribute parms.  */
+/*  */
+/* { dg-do compile } */
+/* { dg-options "-Wnonnull" } */
+
+#include <stddef.h>
+#include <stdlib.h>
+
+void foo(void *bar) __attribute__((nonnull(1)));
+
+void foo(void *bar) { if (!bar) abort(); } /* { dg-warning "nonnull argument" "bar compared to NULL" } */
+
+extern int func (char *, char *, char *, char *) __attribute__((nonnull));
+
+int
+func (char *cp1, char *cp2, char *cp3, char *cp4)
+{
+  if (cp1) /* { dg-warning "nonnull argument" "cp1 compared to NULL" } */
+    return 1;
+
+  if (cp2 == NULL) /* { dg-warning "nonnull argument" "cp2 compared to NULL" } */
+    return 2;
+
+  if (NULL != cp3) /* { dg-warning "nonnull argument" "cp3 compared to NULL" } */
+    return 3;
+
+  return (cp4 != 0) ? 0 : 1; /* { dg-warning "nonnull argument" "cp4 compared to NULL" } */
+}