C PATCH to use NULL_TREE instead of 0 for trees

[Joseph Myers]

On Wed, 17 May 2017, Marek Polacek wrote:

> I've always disliked using 0 where NULL_TREE should be.  It's confusing to see
> if (value != 0), which makes value to look like an integer, even though it may
> be a tree.
> 
> Next cleanup will probablyn be about using booleans where desirable.
> 
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
> 
> 2017-05-17  Marek Polacek  <polacek@redhat.com>
> 
> 	* c-common.c: Use NULL_TREE instead of 0 where appropriate.
> 	* c-warn.c: Likewise.
> 
> 	* c-decl.c: Use NULL_TREE instead of 0 where appropriate.
> 	* c-typeck.c: Likewise.

OK.

-- 
Joseph S. Myers
joseph@codesourcery.com