llvm dev - Jun 2018 - [RFC] Formalizing FileCheck Features

A few replies, then I'll post a revised spec v2 which ought to incorporate
all the other feedback.  If I missed something, give a shout.

Actually, I wish there were a way to do that [constrain DAG to a single line]
for the sake of matching unordered text on a single line.  SAME after DAGs is as
close as I can get to that.  Maybe we need a CHECK-DAG-SAME.

Hmmm. You know, there were cases where people wrote tests that tried to use
combo suffixes like that, but of course those directives were not actually
executed (because they were treated like a SAME with prefix CHECK-DAG (or
whatever), rather than CHECK with two suffixes).  That's why some while ago
I added checks within FileCheck to try to detect duplicate suffixes and
complain.  There were, I don’t remember, a couple dozen or so cases.

After we get the spec done and The Rule implemented, if you want to take a run
at some combo prefixes that had a use-case for you, that could be interesting.

Speaking of wish lists, I've been thinking it would be nice to have some way
to apply a NOT pattern among a range of matches:

CHECK-NOT-PUSH: pattern

Well, there is the `--implicit-check-not` option, which applies to the entire
input text; it looks like you want it just for a subrange, though?  If you
aren't talking about DAGs, then repeating a CHECK-NOT between the other
directives would work although it's pretty tedious (voice of experience) and
easy to mess up (voice of experience).  If you have an example where
CHECK-DAG-NOT would actually be useful, the formalism I'm going for does
seem like it would help.

--paulr

From: Joel E. Denny [mailto:jdenny.ornl at gmail.com]
Sent: Saturday, May 26, 2018 12:11 PM
To: Robinson, Paul
Cc: llvm-dev at lists.llvm.org
Subject: Re: [RFC] Formalizing FileCheck Features

Hi Paul,

On Fri, May 25, 2018 at 10:40 AM, <paul.robinson at
sony.com<mailto:paul.robinson at sony.com>>
wrote:
> Should it be possible for CHECK-SAME match range to include newlines?
It is possible to write a regex that matches newlines.  Doing that in
CHECK-SAME seems a bit odd but I don't think it's worth trying to forbid
it.

OK, so SAME has the sense of matching *starting* on the same line rather than
*within* the same line.  Seems fine.
> I'd note that, in the case of CHECK-NEXT, that choice can restrict what
> CHECK-NEXT can match.  That is, it will complain about a match on the
> previous line rather than skip it and look on the next line.
Ah, so we could define CHECK-NEXT as: move the start of the search
range past the first newline, then behaves as CHECK-SAME?

Right.

But, appending {{.*$}} to the previous pattern should have the same
effect if you have a CHECK-NEXT that runs into that problem.

So the current behavior is more flexible even if less intuitive at first glance
(to me, at least).  It's also more consistent with the way search ranges
work in general.

I think this subtlety and this tip should be mentioned in the user
documentation. Also, because sometimes the previous directive isn't nearby
or could be one of many directives due to multiple check prefixes, the docs
should also offer this formula:

CHECK-SAME: {{.*}}
CHECK-NEXT: your pattern

And I
do think it's valuable for SAME and NEXT to tell you they found
matches but not on the line you asked for. So I'd prefer to leave these
defined as they are.

Agreed.
>> CHECK-NOT: A sequence of NOT directives forms a NOT Group. The group
>> is not executed immediately; instead the next non-NOT directive is
>> executed first, and the start of that directive's match range
becomes
>> the end of the NOT Group's search range.
>
> Based on the following, that wording is not quite right when a DAG
> group follows, so there should probably be some note about that here.
So, "the next non-NOT directive or DAG group is executed ... the start
of that directive or group's match range ..." ?

Sounds good.
>>  (If the next directive is
>> LABEL, it has already executed and has a match range, which is already
>> the end of the search range.)  After the NOT Group's search range
is
>> defined, each NOT directive scans the range for a match, and fails if
>> a match is found.
>>
>> CHECK-DAG: A sequence of DAG directives forms a DAG Group. The group
>> is not executed immediately; instead the next non-DAG directive is
>> executed first, and the start of that directive's match range
becomes
>> the end of the DAG Group's search range.
>
> That's definitely a change from the current behavior.  Currently, the
> DAG group finds its own end based on the farthest match.
Oh good catch.  Copy-thinko from the NOT description.  NOT is the only
kind of directive that has deferred execution.
>>  If the next directive is
>> CHECK-NOT, the end of the DAG Group's search range is
>> unaffected.
>
> Unaffected means that it's as if there's no following directive? 
So
> next CHECK-LABEL (possibly the implicit one at EOF)?  What if there's
> a CHECK, CHECK-NEXT, or CHECK-SAME after all the DAGs and NOTs?
If DAG doesn't have deferred execution then the end of the search range
is the next (explicit or implicit) CHECK-LABEL point, end of story.
>>  After all DAG directives run, the
>> match range for the entire DAG Group extends from the start of the
>> earliest match to the end of the latest match.  The end of that match
>> range becomes the start of the search range for subsequent directives.
>
> That last sentence contradicts the first few sentences: the subsequent
> directive has already been matched.
Right, fixing the previous bug means this sentence says the right thing.

Yep, I agree it's fixed.

> One point not addressed here is the start of the DAG group's search
> range.  Currently, if the DAG group is preceded by a NOT group
> preceded by a DAG group, the last DAG group's search range starts at
> the start of the first DAG group's match range.  Any matches in the
> first DAG group's match range produces a reordering error.  This is
> somewhat similar to the CHECK-SAME and CHECK-NEXT behavior I mentioned
> earlier: the search ranges permit invalid match ranges and then
> complain about them in an effort to diagnose mistakes.  However, that
> restricts what can be matched.
>
> I'm not claiming that either behavior is best.  It's not clear to
me.
> The best use of DAG-NOT-DAG is very confusing to me.  An effort to
> prescribe the right semantics to it needs to be informed by real use
> cases, in my opinion.
I did some email archaeology, and found this exchange on llvm-dev between
myself and Michael Liao (original DAG implementor) 13 Mar 2016:

pr> Commentary in FileCheck itself can easily be interpreted to mean the
pr> intent was that –NOT would scan the region between the points defined
pr> by the last match of the preceding DAG group (which the code gets
pr> right) and the first match of the following DAG group (which the code
pr> does not get right). But the commentary is not really that clear.

ml> That's the intention of the original design. CHECK-NOT never occurs
ml> before we find the start point (the start of file by default) and end
ml> point (the end of file by default.) All other points are through other
ml> CHECKs, including CHECK-DAG but excluding CHECK-NOT.  So that, if you
ml> use CHECK-NOT, you need to be aware of how that range is defined. As
ml> CHECK-DAG pattern matches a group of pattern in any order, the match
ml> point of that group of CHECK-DAG (a consecutive CHECK-DAGs without any
ml> other CHECKs interleaved) is always the point where one of that pgroup
ml> is matched. If one CHECK-DAG is separated by any other CHECKs
ml> (including CHECK-NOT) from preceding CHECK-DAGs, it is not in the
ml> preceding group of CHECK-DAG. That's way how we could check the order
ml> where a group of patterns should never occur before another group of
ml> patterns.

Thanks for digging that up.

So, I believe my specification for the interaction between DAG and NOT
does match the original intent.

I can't argue there.

  Regarding the diagnostic aid, it does
make some sequences really hard to match,

Theoretically, I agree.  But do you know of a real use case where it's a
problem?

and I don't have a general
idea how to fix that (versus {{.*$}} for the similar NEXT situation).

Me neither.

It's also a reasonable continuation of the behavior of plain CHECK, in
that a second CHECK doesn't search the prior text to complain about
ordering issues.

Good point.

The main difference I see is that DAG is specifically about unordered text (and
it might vary from run to run in the parallel programs I'm thinking of), so
the chances of accidental reordering might be higher than with plain CHECK.


SAME and NEXT are, I think, a different category; that has to do with
line-breaks that are not explicitly described by user-written patterns,
and my own experience is that it's helpful to be told that something
matches but isn't on the line I expected.

Agreed.


So, I don't have a definitive answer for changing DAG-NOT-DAG, but
intuitively the spec makes sense to me and my inclination is to think
the diagnostic isn't hugely valuable.

You might be right. Again, I find it hard to think of solid arguments about
DAG-NOT-DAG because it seems like such an unlikely use case.

You mentioned Chris Lattner's point.  DAG-NOT-DAG was the first thing that
came to my mind.

DAG-NOT-DAG is a weird case where (1) you want two or more consecutive but
non-overlapping DAG groups, and (2) you want to exclude certain patterns in
between.  Strangely, with existing directives, you cannot accomplish #1 without
#2, right?  Why do those go together?  It feels like a use case that arose from
an accident in a language specification and not from a real need.

Well, maybe the best approach is just to go with a clear specification (as you
have now) and hope for the best.

>> Putting CHECK-SAME and CHECK-NEXT after CHECK-DAG now has defined
>> behavior, but it's unlikely to be useful.
>
> I believe they had predictable behavior before (their search ranges
> started at the end of the match range for the entire CHECK-DAG), but
> it's different with the above description (they define the end of the
> search range for the preceding CHECK-DAG group).
You're right, it was predictable before, and I am fixing the bug where
the directive after DAG gets executed first so the range isn't affected.

Makes sense, so your specification keeps the old behavior.

Taking Chris Lattner's point into consideration, we might want to say
SAME or NEXT after a DAG should be an error.  But we could also leave
that for a later round.

With your specification, I think the meaning of those cases is clear and
potentially useful.  The only potential problem I see is that people who
haven't studied your specification carefully might think SAME and NEXT
constrain the end of the search range of the DAG group.  It might be worthwhile
to emphasize in the docs that, no, really, DAG does not work that way.

Actually, I wish there were a way to do that for the sake of matching unordered
text on a single line.  SAME after DAGs is as close as I can get to that.  Maybe
we need a CHECK-DAG-SAME.

Speaking of wish lists, I've been thinking it would be nice to have some way
to apply a NOT pattern among a range of matches:

CHECK-NOT-PUSH: pattern
...
CHECK-NOT-POP:

For example, with a pattern of {{.}} and DAGs in between PUSH and POP, I can
check for an unordered set of strings while rejecting any other text among them.
(Now that's a use case for DAG plus NOT that seems very clear to me.)

Like normal NOT, PUSH's action would be deferred until the next directive or
group.  At that point, it would push the specified NOT pattern along with the
next non-NOT directive's match range end as its search range start. POP
would pop and apply those using the previous non-NOT directive's match range
start as its search range end.  The Rule would apply to its matches.  PUSH and
POP would be like normal NOT in terms of their effect on neighboring directives:
each would terminate any preceding DAG group, and, because there's no match
in a successful run, each would have no effect on any neighboring
directive's search range.  PUSH and POP with no directives in between other
than those in the NOT family would be an error.

Your formal specification of FileCheck makes it straight-forward to describe
this behavior precisely.


--paulr

P.S. I am away next week but expect to keep an eye on the lists.

Sure.  Have fun.  No rush.

Thanks.

Joel

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Spec for the model, version 2.  If this survives I'll start on
amendments to the FileCheck doc.
--paulr


Basic Conceptual Model
----------------------

FileCheck should operate on the basis of these three fundamental
concepts.

(1) Search range.  This is some substring of the input text where one
or more directives will do their pattern-matching magic.

(2) Match range.  This is a substring of a search range where a
directive (or in one case, a group of directives) has matched a
pattern.

(3) Directive groups.  These are sequences of adjacent directives that
operate in a related way on a search range.  Directives within a group
are processed in order, except as noted in the directive description.

Finally we add The Rule:  No match ranges may overlap.


Directive Descriptions Based On Conceptual Model
------------------------------------------------

Given the conceptual model, all directives can be defined in terms of
it.

CHECK: Scans the search range for a pattern match. Fails if no match
is found.  The end of the match range becomes the start of the search
range for subsequent directives.

CHECK-SAME: Like CHECK, plus there must be zero newlines within the
search range prior to the start of the match range.

CHECK-NEXT: Like CHECK, plus there must be exactly one newline within
the search range prior to the start of the match range.

Note: This definition means CHECK-NEXT will fail if the pattern
occurs both on the line where the search range starts, and on the
(expected) next line.  This can be avoided by putting a
`CHECK-SAME: {{.*}}` before the CHECK-NEXT.  We could also avoid
this by defining the CHECK-NEXT search range to be just the following
line of text.  We define CHECK-NEXT the way we do because it seems 
valuable to diagnose mismatches that are simply on the wrong line,
and the problematic case is rare.

CHECK-LABEL: All LABEL directives are processed before any other
directives.  These directives have three effects.  First, they act like
CHECK directives. Second, they partition the input text into disjoint
search ranges, delimited by the match ranges of the LABEL directives.
Third, they partition the remaining directives into Label Groups,
each of which operates on the corresponding search range.  For truly
pedantic formalism, we can say there are implicit LABEL directives
matching the start and end of the entire input text, thus all
non-LABEL directives are always in some Label Group and there is
really nothing special about the end of the input text.

CHECK-NOT: A sequence of one or more consecutive NOT directives forms
a NOT Group. The group is not executed immediately; instead the next 
non-NOT directive (or DAG Group, if the next directive is DAG) is 
executed first, and the start of that directive's (or group's)
match range becomes the end of the NOT Group's search range.  (If the 
next directive is LABEL, it has already executed and has a match range, 
which is already the end of the search range.  If the NOT is the last
directive, the search range extends to the end of the input.)  After 
the NOT Group's search range is defined, each NOT directive in the
group scans the range for a match, and fails if a match is found.

CHECK-DAG: A sequence of one or more consecutive DAG directives forms
a DAG Group. The search range for the group extends from the end of
the previous match (or start of the input, if there is no previous
directive) to the start of the next LABEL match, or to the end of the
input if there is no later LABEL.  Each directive in the DAG group 
scans the search range of the group looking for a pattern match. A 
directive fails if no match is found. Per The Rule, match ranges for
the individual DAG directives in a group may not overlap.  After all 
DAG directives run, the match range for the entire DAG Group extends 
from the start of the earliest match to the end of the latest match.  
The end of that match range becomes the start of the search range for 
subsequent directives.

Observations
------------

A CHECK-NOT surrounded by CHECK-DAG directives separates the DAGs into
disjoint groups, and does not permit matches from the two groups to
overlap. DAG was originally implemented to detect and diagnose an
overlap in this situation, but the implementation worked only for the 
first DAG after a NOT. This can lead to counter-intuitive behavior and 
potentially makes certain kinds of matches impossible.


Technically, putting CHECK-SAME or CHECK-NEXT after CHECK-DAG has 
defined behavior, but it's unlikely to be useful, so FileCheck rejects
that kind of sequence.  Similarly, putting SAME or NEXT as the
first directive in a file likewise has defined behavior (matching
precisely the first or second line respectively of the input text);
however this is far more likely to be a mistake than to be useful, so
again FileCheck rejects this.

Hi Paul,

I've inlined some minor suggestions and questions.

On Thu, Jun 14, 2018 at 4:38 PM, <paul.robinson at sony.com> wrote:
> Spec for the model, version 2.  If this survives I'll start on
> amendments to the FileCheck doc.
> --paulr
>
>
> Basic Conceptual Model
> ----------------------
>
> FileCheck should operate on the basis of these three fundamental
> concepts.
>
"should operate" -> "operates"

>
> (1) Search range.  This is some substring of the input text where one
> or more directives will do their pattern-matching magic.
>
> (2) Match range.  This is a substring of a search range where a
> directive (or in one case, a group of directives) has matched a
> pattern.
>
> (3) Directive groups.  These are sequences of adjacent directives that
> operate in a related way on a search range.  Directives within a group
> are processed in order, except as noted in the directive description.
>
Is there an exception?

>
> Finally we add The Rule:  No match ranges may overlap.
>
>
> Directive Descriptions Based On Conceptual Model
> ------------------------------------------------
>
> Given the conceptual model, all directives can be defined in terms of
> it.
>
> CHECK: Scans the search range for a pattern match. Fails if no match
> is found.  The end of the match range becomes the start of the search
> range for subsequent directives.
>
> CHECK-SAME: Like CHECK, plus there must be zero newlines within the
> search range prior to the start of the match range.
>
> CHECK-NEXT: Like CHECK, plus there must be exactly one newline within
> the search range prior to the start of the match range.
>
> Note: This definition means CHECK-NEXT will fail if the pattern
> occurs both on the line where the search range starts, and on the
> (expected) next line.

The first occurrence is sufficient for a failure.  Perhaps: "and on
the" ->
"even if it also occurs on the"

>   This can be avoided by putting a
> `CHECK-SAME: {{.*}}` before the CHECK-NEXT.  We could also avoid
>
To make it clearer to the naive user you're not describing a second option
he can also try as a user: "We could also avoid" -> "We could
have
implemented FileCheck to avoid"

> this by defining the CHECK-NEXT search range to be just the following
> line of text.  We define CHECK-NEXT the way we do because it seems
> valuable to diagnose mismatches that are simply on the wrong line,
> and the problematic case is rare.
>
By the way, do you think it would be helpful for the diagnostic to suggest
the CHECK-SAME trick?

CHECK-LABEL: All LABEL directives are processed before any
other
> directives.  These directives have three effects.  First, they act like
> CHECK directives. Second, they partition the input text into disjoint
> search ranges, delimited by the match ranges of the LABEL directives.
> Third, they partition the remaining directives into Label Groups,
> each of which operates on the corresponding search range.  For truly
> pedantic formalism, we can say there are implicit LABEL directives
> matching the start and end of the entire input text, thus all
> non-LABEL directives are always in some Label Group and there is
> really nothing special about the end of the input text.
>
> CHECK-NOT: A sequence of one or more consecutive NOT directives forms
> a NOT Group. The group is not executed immediately; instead the next
> non-NOT directive (or DAG Group, if the next directive is DAG) is
> executed first, and the start of that directive's (or group's)
> match range becomes the end of the NOT Group's search range.  (If the
> next directive is LABEL, it has already executed and has a match range,
> which is already the end of the search range.  If the NOT is the last
> directive, the search range extends to the end of the input.)  After
> the NOT Group's search range is defined, each NOT directive in the
> group scans the range for a match, and fails if a match is found.
>
> CHECK-DAG: A sequence of one or more consecutive DAG directives forms
> a DAG Group. The search range for the group extends from the end of
> the previous match (or start of the input, if there is no previous
>
directive) to the start of the next LABEL match, or to the end of
the
> input if there is no later LABEL.

It reads to me like LABEL is relevant to the end but not the start.  You
might replace "(or start of the input" with "(possibly a LABEL or
start of
the input".

On the other hand, in most of your directive descriptions (see CHECK,
CHECK-NEXT, and CHECK-SAME), you don't define the directive's own search
range.  Instead, you define how that directive impacts the start of the
next search range.

The only difference here is that you have an entire group of directives
with the same search range.  As FileCheck grows new directives, perhaps a
more maintainable way to describe the search ranges for NOT groups and DAG
groups is as follows:

"The search range for every member of the group is the search range that
any single CHECK directive would have if it were to replace the entire
group."

  Each directive in the DAG group
> scans the search range of the group looking for a pattern match. A
> directive fails if no match is found. Per The Rule, match ranges for
> the individual DAG directives in a group may not overlap.

The last sentence is ambiguous.  It could mean you'll get a diagnostic if
they do overlap.  Perhaps say "Per The Rule, each group member skips past
any match whose range overlaps the range of an earlier group member's
match."


>   After all
> DAG directives run, the match range for the entire DAG Group extends
> from the start of the earliest match to the end of the latest match.
> The end of that match range becomes the start of the search range for
> subsequent directives.
>
> Observations
> ------------
>
> A CHECK-NOT surrounded by CHECK-DAG directives separates the DAGs into
>
"A CHECK-NOT" -> "One or more CHECK-NOTs"
>
> disjoint groups, and does not permit matches from the two groups to
> overlap. DAG was originally implemented to detect and diagnose an
> overlap in this situation, but the implementation worked only for the
> first DAG after a NOT. This can lead to counter-intuitive behavior and
> potentially makes certain kinds of matches impossible.
>
By the way, I have a patch that fixes the search ranges for DAG-NOT-DAG to
match your formal description here.  I need to polish up the commit log,
and then I'll post it for review.  It applies after my other patches
because it was easier to implement that way.

Thanks.

Joel

>
>
> Technically, putting CHECK-SAME or CHECK-NEXT after CHECK-DAG has
> defined behavior, but it's unlikely to be useful, so FileCheck rejects
> that kind of sequence.  Similarly, putting SAME or NEXT as the
> first directive in a file likewise has defined behavior (matching
> precisely the first or second line respectively of the input text);
> however this is far more likely to be a mistake than to be useful, so
> again FileCheck rejects this.
>
>
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Hi Paul,

On Thu, Jun 14, 2018 at 4:29 PM, <paul.robinson at sony.com>
wrote:
>
> Speaking of wish lists, I've been thinking it would be nice to have
some
> way to apply a NOT pattern among a range of matches:
>
>
>
> CHECK-NOT-PUSH: pattern
>
>
>
> Well, there is the `--implicit-check-not` option, which applies to the
> entire input text; it looks like you want it just for a subrange, though?
>
Right.

>   If you aren't talking about DAGs, then repeating a CHECK-NOT between
the
> other directives would work although it's pretty tedious (voice of
> experience) and easy to mess up (voice of experience).
>
Agreed.

> If you have an example where CHECK-DAG-NOT would actually be useful,
>
Yes, but I'd prefer a more general construct that also works without DAG.
That's why I suggested CHECK-NOT-PUSH and POP.  Jessica Paquette described
a use case that I thought suggested she could benefit from that too, but
it's possible I misunderstood her:

http://lists.llvm.org/pipermail/llvm-dev/2018-May/123092.html

> the formalism I'm going for does seem like it would help.
>
Seems to help with either approach.

Thanks.

Joel

>
>
> --paulr
>
>
>
> *From:* Joel E. Denny [mailto:jdenny.ornl at gmail.com]
> *Sent:* Saturday, May 26, 2018 12:11 PM
> *To:* Robinson, Paul
> *Cc:* llvm-dev at lists.llvm.org
> *Subject:* Re: [RFC] Formalizing FileCheck Features
>
>
>
> Hi Paul,
>
>
>
> On Fri, May 25, 2018 at 10:40 AM, <paul.robinson at sony.com> wrote:
>
> > Should it be possible for CHECK-SAME match range to include newlines?
>
> It is possible to write a regex that matches newlines.  Doing that in
> CHECK-SAME seems a bit odd but I don't think it's worth trying to
forbid
> it.
>
>
>
> OK, so SAME has the sense of matching *starting* on the same line rather
> than *within* the same line.  Seems fine.
>
>
>
> > I'd note that, in the case of CHECK-NEXT, that choice can restrict
what
> > CHECK-NEXT can match.  That is, it will complain about a match on the
> > previous line rather than skip it and look on the next line.
>
> Ah, so we could define CHECK-NEXT as: move the start of the search
> range past the first newline, then behaves as CHECK-SAME?
>
>
>
> Right.
>
>
>
> But, appending {{.*$}} to the previous pattern should have the same
> effect if you have a CHECK-NEXT that runs into that problem.
>
>
>
> So the current behavior is more flexible even if less intuitive at first
> glance (to me, at least).  It's also more consistent with the way
search
> ranges work in general.
>
>
>
> I think this subtlety and this tip should be mentioned in the user
> documentation. Also, because sometimes the previous directive isn't
nearby
> or could be one of many directives due to multiple check prefixes, the docs
> should also offer this formula:
>
>
>
> CHECK-SAME: {{.*}}
>
> CHECK-NEXT: your pattern
>
>
>
> And I
> do think it's valuable for SAME and NEXT to tell you they found
> matches but not on the line you asked for. So I'd prefer to leave these
> defined as they are.
>
>
>
> Agreed.
>
>
>
> >> CHECK-NOT: A sequence of NOT directives forms a NOT Group. The
group
> >> is not executed immediately; instead the next non-NOT directive is
> >> executed first, and the start of that directive's match range
becomes
> >> the end of the NOT Group's search range.
> >
> > Based on the following, that wording is not quite right when a DAG
> > group follows, so there should probably be some note about that here.
>
> So, "the next non-NOT directive or DAG group is executed ... the start
> of that directive or group's match range ..." ?
>
>
>
> Sounds good.
>
>
>
> >>  (If the next directive is
> >> LABEL, it has already executed and has a match range, which is
already
> >> the end of the search range.)  After the NOT Group's search
range is
> >> defined, each NOT directive scans the range for a match, and fails
if
> >> a match is found.
> >>
> >> CHECK-DAG: A sequence of DAG directives forms a DAG Group. The
group
> >> is not executed immediately; instead the next non-DAG directive is
> >> executed first, and the start of that directive's match range
becomes
> >> the end of the DAG Group's search range.
> >
> > That's definitely a change from the current behavior.  Currently,
the
> > DAG group finds its own end based on the farthest match.
>
> Oh good catch.  Copy-thinko from the NOT description.  NOT is the only
> kind of directive that has deferred execution.
>
> >>  If the next directive is
> >> CHECK-NOT, the end of the DAG Group's search range is
> >> unaffected.
> >
> > Unaffected means that it's as if there's no following
directive?  So
> > next CHECK-LABEL (possibly the implicit one at EOF)?  What if
there's
> > a CHECK, CHECK-NEXT, or CHECK-SAME after all the DAGs and NOTs?
>
> If DAG doesn't have deferred execution then the end of the search range
> is the next (explicit or implicit) CHECK-LABEL point, end of story.
>
>
>
> >>  After all DAG directives run, the
> >> match range for the entire DAG Group extends from the start of the
> >> earliest match to the end of the latest match.  The end of that
match
> >> range becomes the start of the search range for subsequent
directives.
> >
> > That last sentence contradicts the first few sentences: the subsequent
> > directive has already been matched.
>
> Right, fixing the previous bug means this sentence says the right thing.
>
>
>
> Yep, I agree it's fixed.
>
>
>
>
> > One point not addressed here is the start of the DAG group's
search
> > range.  Currently, if the DAG group is preceded by a NOT group
> > preceded by a DAG group, the last DAG group's search range starts
at
> > the start of the first DAG group's match range.  Any matches in
the
> > first DAG group's match range produces a reordering error.  This
is
> > somewhat similar to the CHECK-SAME and CHECK-NEXT behavior I mentioned
> > earlier: the search ranges permit invalid match ranges and then
> > complain about them in an effort to diagnose mistakes.  However, that
> > restricts what can be matched.
> >
> > I'm not claiming that either behavior is best.  It's not clear
to me.
> > The best use of DAG-NOT-DAG is very confusing to me.  An effort to
> > prescribe the right semantics to it needs to be informed by real use
> > cases, in my opinion.
>
> I did some email archaeology, and found this exchange on llvm-dev between
> myself and Michael Liao (original DAG implementor) 13 Mar 2016:
>
> pr> Commentary in FileCheck itself can easily be interpreted to mean the
> pr> intent was that –NOT would scan the region between the points
defined
> pr> by the last match of the preceding DAG group (which the code gets
> pr> right) and the first match of the following DAG group (which the
code
> pr> does not get right). But the commentary is not really that clear.
>
> ml> That's the intention of the original design. CHECK-NOT never
occurs
> ml> before we find the start point (the start of file by default) and
end
> ml> point (the end of file by default.) All other points are through
other
> ml> CHECKs, including CHECK-DAG but excluding CHECK-NOT.  So that, if
you
> ml> use CHECK-NOT, you need to be aware of how that range is defined. As
> ml> CHECK-DAG pattern matches a group of pattern in any order, the match
> ml> point of that group of CHECK-DAG (a consecutive CHECK-DAGs without
any
> ml> other CHECKs interleaved) is always the point where one of that
pgroup
> ml> is matched. If one CHECK-DAG is separated by any other CHECKs
> ml> (including CHECK-NOT) from preceding CHECK-DAGs, it is not in the
> ml> preceding group of CHECK-DAG. That's way how we could check the
order
> ml> where a group of patterns should never occur before another group of
> ml> patterns.
>
>
>
> Thanks for digging that up.
>
>
>
> So, I believe my specification for the interaction between DAG and NOT
> does match the original intent.
>
>
>
> I can't argue there.
>
>
>
>   Regarding the diagnostic aid, it does
> make some sequences really hard to match,
>
>
>
> Theoretically, I agree.  But do you know of a real use case where it's
a
> problem?
>
>
>
> and I don't have a general
>
> idea how to fix that (versus {{.*$}} for the similar NEXT situation).
>
>
>
> Me neither.
>
>
>
> It's also a reasonable continuation of the behavior of plain CHECK, in
> that a second CHECK doesn't search the prior text to complain about
> ordering issues.
>
>
>
> Good point.
>
>
>
> The main difference I see is that DAG is specifically about unordered text
> (and it might vary from run to run in the parallel programs I'm
thinking
> of), so the chances of accidental reordering might be higher than with
> plain CHECK.
>
>
>
>
> SAME and NEXT are, I think, a different category; that has to do with
> line-breaks that are not explicitly described by user-written patterns,
> and my own experience is that it's helpful to be told that something
> matches but isn't on the line I expected.
>
>
>
> Agreed.
>
>
>
>
> So, I don't have a definitive answer for changing DAG-NOT-DAG, but
> intuitively the spec makes sense to me and my inclination is to think
> the diagnostic isn't hugely valuable.
>
>
>
> You might be right. Again, I find it hard to think of solid arguments
> about DAG-NOT-DAG because it seems like such an unlikely use case.
>
>
>
> You mentioned Chris Lattner's point.  DAG-NOT-DAG was the first thing
that
> came to my mind.
>
>
>
> DAG-NOT-DAG is a weird case where (1) you want two or more consecutive but
> non-overlapping DAG groups, and (2) you want to exclude certain patterns in
> between.  Strangely, with existing directives, you cannot accomplish #1
> without #2, right?  Why do those go together?  It feels like a use case
> that arose from an accident in a language specification and not from a real
> need.
>
>
>
> Well, maybe the best approach is just to go with a clear specification (as
> you have now) and hope for the best.
>
>
>
>
> >> Putting CHECK-SAME and CHECK-NEXT after CHECK-DAG now has defined
> >> behavior, but it's unlikely to be useful.
> >
> > I believe they had predictable behavior before (their search ranges
> > started at the end of the match range for the entire CHECK-DAG), but
> > it's different with the above description (they define the end of
the
> > search range for the preceding CHECK-DAG group).
>
> You're right, it was predictable before, and I am fixing the bug where
> the directive after DAG gets executed first so the range isn't
affected.
>
>
>
> Makes sense, so your specification keeps the old behavior.
>
>
>
> Taking Chris Lattner's point into consideration, we might want to say
> SAME or NEXT after a DAG should be an error.  But we could also leave
> that for a later round.
>
>
>
> With your specification, I think the meaning of those cases is clear and
> potentially useful.  The only potential problem I see is that people who
> haven't studied your specification carefully might think SAME and NEXT
> constrain the end of the search range of the DAG group.  It might be
> worthwhile to emphasize in the docs that, no, really, DAG does not work
> that way.
>
>
>
> Actually, I wish there were a way to do that for the sake of matching
> unordered text on a single line.  SAME after DAGs is as close as I can get
> to that.  Maybe we need a CHECK-DAG-SAME.
>
>
>
> Speaking of wish lists, I've been thinking it would be nice to have
some
> way to apply a NOT pattern among a range of matches:
>
>
>
> CHECK-NOT-PUSH: pattern
>
> ...
>
> CHECK-NOT-POP:
>
>
>
> For example, with a pattern of {{.}} and DAGs in between PUSH and POP, I
> can check for an unordered set of strings while rejecting any other text
> among them. (Now that's a use case for DAG plus NOT that seems very
clear
> to me.)
>
>
>
> Like normal NOT, PUSH's action would be deferred until the next
directive
> or group.  At that point, it would push the specified NOT pattern along
> with the next non-NOT directive's match range end as its search range
> start. POP would pop and apply those using the previous non-NOT
directive's
> match range start as its search range end.  The Rule would apply to its
> matches.  PUSH and POP would be like normal NOT in terms of their effect on
> neighboring directives: each would terminate any preceding DAG group, and,
> because there's no match in a successful run, each would have no effect
on
> any neighboring directive's search range.  PUSH and POP with no
> directives in between other than those in the NOT family would be an error.
>
>
>
> Your formal specification of FileCheck makes it straight-forward to
> describe this behavior precisely.
>
>
>
>
> --paulr
>
> P.S. I am away next week but expect to keep an eye on the lists.
>
>
>
> Sure.  Have fun.  No rush.
>
>
>
> Thanks.
>
>
>
> Joel
>
>
>
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