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Date:   Wed, 26 Apr 2023 19:16:16 -0400
From:   "Theodore Ts'o" <tytso@mit.edu>
To:     Nick Desaulniers <ndesaulniers@google.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Nathan Chancellor <nathan@kernel.org>,
        linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [GIT PULL] ext4 changes for the 6.4 merge window
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On Wed, Apr 26, 2023 at 03:07:48PM -0700, Nick Desaulniers wrote:
> Is this what you had in mind?
> ```
> $ cat linus.c
> #define NULL ((void*)0)
> 
> void * _Nonnull foo (void) {
>     return &foo;
> }
> 
> void bar (void) {
>     if (foo() == NULL) // maybe should warn that foo() returns _Nonnull?
>         bar();
> }
>
> $ clang linus.c -fsyntax-only
> linus.c:8:15: warning: comparison of _Nonnull function call 'foo'
> equal to a null pointer is always false

Ideally, the warning should also fire in this case:

    if (!foo()) {
    	bar();
    }

And of course, what if the code does this:

    p = foo();
    if (p) {
    	quux();
    }

Would these also be considered implicit comparisons to a NULL pointer?

	    	       	       	  - Ted