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

1 files changed, 3 insertions, 0 deletions

diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 403cebe..518d689 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.