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Date:   Wed, 1 Apr 2020 14:20:15 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Julien Thierry <jthierry@redhat.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>, tglx@linutronix.de,
        linux-kernel@vger.kernel.org, x86@kernel.org, mhiramat@kernel.org,
        mbenes@suse.cz
Subject: Re: [PATCH v2] objtool,ftrace: Implement UNWIND_HINT_RET_OFFSET
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On Wed, 1 Apr 2020 19:45:44 +0200
Peter Zijlstra <peterz@infradead.org> wrote:

> > I believe what Julien is saying is the above logic is equivalent:
> > 
> > 	if (x != y &&
> > 	    !(z && x == y + z))
> > 
> > is the same as:
> > 
> > 	if (x != y + z)  
> 
> It is not, the former will accept either x==y || x==y+z, while the
> latter will only accept x==y+z.

No, the former accepts:

	x==y || (z && x == y + z)

Which is the same as: x == y + z

As the second condition is only tested if z != 0, and x ==  y is the same
as x == y + 0

-- Steve