[llvm-dev] FileCheck: combining -DAG and -NOT

[David Blaikie via llvm-dev]

Yeah, fair - thanks for the explanation/correction/etc.

That does seem a bit odd. Dunno.

On Mon, Mar 7, 2016 at 10:54 PM, Robinson, Paul <
Paul_Robinson at playstation.sony.com> wrote:

> Nope.  Sorry, your expectation is incorrect.
>
> "BETWEEN BEFORE AFTER" would be accepted, because: (1) the first –DAG
> matches BEFORE; (2) the –NOT range starts at the preceding match-point,
> i.e. the (end of the) BEFORE, thus does not find BETWEEN; (3) the second
> –DAG starts at the same point as the –NOT.
>
> That is, the first –DAG and the following –NOT *are* ordered; the –NOT and
> the subsequent –DAG are *not* ordered.
>
> You most certainly cannot intermix them freely and expect them all to look
> at the same range; that is explicitly not the documented (or actual)
> behavior.
>
> --paulr
>
>
>
> *From:* David Blaikie [mailto:dblaikie at gmail.com]
> *Sent:* Monday, March 07, 2016 8:43 PM
> *To:* Robinson, Paul
> *Cc:* llvm-dev at lists.llvm.org
> *Subject:* Re: [llvm-dev] FileCheck: combining -DAG and -NOT
>
>
>
> I'd probably have expected the behavior it has - that -DAG and -NOT are
> not ordered with respect to each other, and form a bag of things ordered
> with respect to enclosing CHECK:s.
>
> If you want to try turning it into an error, you could find all the places
> we do use interspersed -DAG and -NOT and have a discussion about whether
> they're more buggy than they are useful/correct.
>
>
>
> On Mon, Mar 7, 2016 at 5:39 PM, Robinson, Paul via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
> If you look at the FileCheck documentation page:
> http://llvm.org/docs/CommandGuide/FileCheck.html
> you'll find this intriguing example of combining -DAG with -NOT
> (slightly amended to avoid some potential confusion):
>
> ; CHECK-DAG: BEFORE
> ; CHECK-NOT: BETWEEN
> ; CHECK-DAG: AFTER
>
> The page says this will reject the sequence "AFTER BEFORE", which is
> correct.  It's intuitively obvious that it will also reject the text
> "BEFORE BETWEEN AFTER" as well.
>
> Pop Quiz:  Will it accept or reject "BEFORE AFTER BETWEEN"?
> No, don't go try it, that's cheating; what do you *think* will happen?
> Take a minute, I won't mind.
> ---
>
> So, here's the story.
>
> Normally a -NOT line will scan the text between the points where the
> preceding and following CHECK lines match.  By that mental model, you'd
> expect the first -DAG to find BEFORE, the second -DAG to find AFTER, and
> then -NOT would verify the absence of "BETWEEN" between those two points.
> All very intuitive, and I've certainly seen tests written to expect that.
>
> However, things get a little funky when you have -NOT followed by -DAG.
> What's the endpoint of the -NOT search?  The thing that follows isn't
> a CHECK, it's a CHECK-DAG, except that -NOT is already kind of DAG-ish
> so you have two DAG-ish groups staring at each other wondering who will
> go first.
>
> In this case, turns out, it's the -NOT who blinks first.  The endpoint
> of the search is implicitly the end-of-input.  The Pop Quiz answer is:
> *Rejected.*  The BETWEEN occurs after BEFORE, and before the end-of-input.
>
> Here's the real question:  *Should* FileCheck run the second -DAG group
> before it runs the -NOT group?  Then the range for the -NOT would be
> bounded by the matching points for the surrounding -DAG lines, which
> probably matches what basically everybody expects to happen.
>
> Or, leave things as they are, and add a cautionary tale to the FileCheck
> documentation page?  Given there's an actual documentation example, it
> would seem inappropriate to make it an *error* if a -NOT is followed
> by a -DAG!
>
> Thanks,
> --paulr
>
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