Warn when comparing nonnull arguments to NULL in a function.

From d8d71393c2fde83769d00c2da766a2fa7955ecbb Mon Sep 17 00:00:00 2001
From: Mark Wielaard <mjw@redhat.com>
Date: Wed, 9 Sep 2015 23:26:54 +0200
Subject: [PATCH] Warn when comparing nonnull arguments to NULL in a function.
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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.
---
 gcc/ChangeLog                          |  4 ++++
 gcc/c/ChangeLog                        |  5 +++++
 gcc/c/c-typeck.c                       | 10 ++++++++++
 gcc/cp/ChangeLog                       |  5 +++++
 gcc/cp/typeck.c                        | 10 ++++++++++
 gcc/doc/invoke.texi                    |  3 +++
 gcc/testsuite/ChangeLog                |  4 ++++
 gcc/testsuite/c-c++-common/nonnull-1.c | 28 ++++++++++++++++++++++++++++
 8 files changed, 69 insertions(+)
 create mode 100644 gcc/testsuite/c-c++-common/nonnull-1.c

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 618bbe6..86038f5 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,7 @@ 
+2015-09-09  Mark Wielaard  <mjw@redhat.com>
+
+	* doc/invoke.texi (Wnonnull): Also warns when comparing against NULL.
+
 2015-09-09  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
 
 	* config/arm/arm.md (*subsi3_compare0): Rename to...
diff --git a/gcc/c/ChangeLog b/gcc/c/ChangeLog
index d7eeb2d..35ccdda 100644
--- a/gcc/c/ChangeLog
+++ b/gcc/c/ChangeLog
@@ -1,3 +1,8 @@ 
+2015-09-09  Mark Wielaard  <mjw@redhat.com>
+
+	* c-typeck.c (build_binary_op): Check and warn when nonnull arg
+	parm against NULL.
+
 2015-09-09  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c/67501
diff --git a/gcc/c/c-typeck.c b/gcc/c/c-typeck.c
index dc22396..4108f27 100644
--- a/gcc/c/c-typeck.c
+++ b/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)))
 	    {
diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 515a1e8..7cf0064 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,8 @@ 
+2015-09-09  Mark Wielaard  <mjw@redhat.com>
+
+	* typeck.c (cp_build_binary_op): Check and warn when nonnull arg
+	parm against NULL.
+
 2015-09-09  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c++/67504
diff --git a/gcc/cp/typeck.c b/gcc/cp/typeck.c
index 388558c..482e42c 100644
--- a/gcc/cp/typeck.c
+++ b/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);
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 76e5e29..dc171ec 100644
--- a/gcc/doc/invoke.texi
+++ b/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.
 
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 360fe70..345caee 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@ 
+2015-09-09  Mark Wielaard  <mjw@redhat.com>
+
+	* c-c++-common/nonnull-1.c: New test.
+
 2015-09-09  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
 
 	* gcc.target/aarch64/mod_2.x: New file.
diff --git a/gcc/testsuite/c-c++-common/nonnull-1.c b/gcc/testsuite/c-c++-common/nonnull-1.c
new file mode 100644
index 0000000..744c45f
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/nonnull-1.c
@@ -0,0 +1,28 @@ 
+/* 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 "null" "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" } */
+}
-- 
2.4.3