Re: [RFC v0 0/4] Give a type to constants too

From: Christopher Li <sparse@chrisli.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Dibyendu Majumdar <mobile@majumdar.org.uk>,
	Luc Van Oostenryck <luc.vanoostenryck@gmail.com>,
	Sparse Mailing-list <linux-sparse@vger.kernel.org>,
	Jeff Garzik <jeff@garzik.org>, Pekka Enberg <penberg@kernel.org>
Subject: Re: [RFC v0 0/4] Give a type to constants too
Date: Thu, 10 Aug 2017 11:25:41 -0400	[thread overview]
Message-ID: <CANeU7Qmmopaz-+Vf6sQpJ_UTuvXpKxRhmPMKXqO7XGikjF+d=g@mail.gmail.com> (raw)
In-Reply-To: <CA+55aFzWLUXdTPRRfyN+SCxDvedZ4pnCOcaYMQ17zLA-id3tJQ@mail.gmail.com>

On Thu, Mar 16, 2017 at 4:43 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Thu, Mar 16, 2017 at 1:19 PM, Dibyendu Majumdar
> <mobile@majumdar.org.uk> wrote:
>>
>> The issue is not with the type of %r6 but %arg3 and %arg4 if these
>> happen to be integer constants, and the function is variadic so we
>> cannot work out the type from the function prototype.
>
> Yes. Ok, I see the problem.
>
> I think we could add a 'size' to the pseudo, and solve it that way.
> CSE and other linearization artifacts may mean that the type is
> undefined, but the size should be well-defined.

Sorry for not able to join the discussion earlier. I am catching up
my backlogs of discussion. I have think about this for a while now.
I think there is one alternative solution is just give set_val instruction
a size (not type).

reason being:
1) Necessary for CSE as well.
   If CSE combine two set_val of different size as one pesudo.
   and it is used as two different size. That is likely a bug.
   That is independent of having OP_PUSH or not.

2) Sufficient.
   If we have the size of set_val, we can solve the problem of
   calling function with instant constants and the function is variadic.

That is likely the minimal required change to get both issue
resolved.

Thanks

Chris