llvm dev - May 2018 - RFC: [FileCheck] CHECK-DAG for multiple occurrences of string

On Mon, May 7, 2018 at 12:56 PM, <paul.robinson at sony.com> wrote:
> > 1. In a CHECK-DAG group, don't let the matches for patterns
overlap.
> > 2. Add a new CHECK-DAG-N directive, where N is some integer, to
express
> > that a pattern must have N non-overlapping matches.
>
> I think #1 is much more intuitive and easy to describe/document than #2.
> Changing the meaning of DAG in that way is highly unlikely to affect any
> existing test, IMO.  And if it does, my first expectation is that the test
> wasn't doing what the author intended anyway.
>
I implemented #1, and I now have 105 new unexpected tests failures from
llvm core (58), clang (45), openmp runtime (1), and compiler-rt (1) test
suites.

I've only looked at a few failures so far.  Of those, the problem is the
expected one: in a CHECK-DAG group, multiple patterns match the same line,
so not permitting overlapping matches causes some patterns never to match
successfully.  However, all the overlapping matches so far seem
unintentional.  That is, this new implementation seems to be catching test
errors.

Here are some scenarios I found:

S1. Patterns sometimes identical
--------------------------------

For example, tools/clang/test/OpenMP/for_codegen.cpp has:

```
// TERM_DEBUG-DAG: [[DBG_LOC_START]] = !DILocation(line: [[@LINE-15]],
// TERM_DEBUG-DAG: [[DBG_LOC_END]] = !DILocation(line: [[@LINE-16]],
// TERM_DEBUG-DAG: [[DBG_LOC_CANCEL]] = !DILocation(line: [[@LINE-17]],
```

Patterns are the same except for the names of regex variables referenced.
The variables happen to have the same value, so the patterns match the same
line when overlapping is permitted.

Perhaps the test was designed to handle the possibility that the variables
might have different values one day, and not permitting overlapping matches
would break that case.  My guess is that this was actually unintentional,
so my solution is to rename all the variables to DBG_LOC and remove two of
the above patterns.

S2. Superset before subset
--------------------------

For example, tools/clang/test/OpenMP/target_parallel_codegen.cpp has this:

```
// CHECK-DAG:   store i[[SZ]] {{4|8}}, i[[SZ]]* {{%[^,]+}}
...
// CHECK-DAG:   store i[[SZ]] 4, i[[SZ]]* {{%[^,]+}}
```

Some pattern X matches a superset of some pattern Y.  X appears before Y,
but Y's intended match appears before X's intended match in the output.
The result is that X matches Y's intended match.  If overlapping is not
permitted, Y has nothing to match, and FileCheck complains.  If overlapping
is permitted, Y also matches Y's intended match, and X's intended match
is
quietly ignored.  This case is clearly unintentional.  One fix is to move X
after Y.  A cleaner fix is to somehow make X distinct.

Another example of this scenario:

* test/Bitcode/thinlto-function-summary-originalnames.ll

S3. Wrong number of identical patterns
--------------------------------------

This scenario is just an incorrect attempt at the original use case I
wanted to address.

For example,
projects/openmp/runtime/test/ompt/parallel/not_enough_threads.c repeats the
following three times:

```
// CHECK-DAG: {{^}}[[THREAD_ID:[0-9]+]]: ompt_event_implicit_task_begin:
parallel_id=[[PARALLEL_ID]], task_id=[[IMPLICIT_TASK_ID:[0-9]+]]
// CHECK-DAG: {{^}}[[THREAD_ID]]: ompt_event_barrier_begin:
parallel_id=[[PARALLEL_ID]], task_id=[[IMPLICIT_TASK_ID]]
```

The author was obviously expecting CHECK-DAG not to permit overlapping
matches and wanted to check that the above lines appeared three times.
Specifically, he's expecting 3 threads after the master thread, but the run
line sets OMP_THREAD_LIMIT=2.  If overlapping matches are permitted, this
will permit any non-zero number of threads after the master thread.  If
overlapping matches are not permitted, we must increase OMP_THREAD_LIMIT to
at least 4 or reduce the number of pattern repetitions.

S4. CHECK-DAG unneeded
----------------------

For example, test/CodeGen/AMDGPU/store-v3i64.ll has:

```
; GCN-DAG: buffer_store_byte v
; GCN-DAG: buffer_store_byte v
; GCN-DAG: buffer_store_byte v
```

The intention appears to be the same as S3: match a pattern N times.
However, this example doesn't actually need CHECK-DAG at all.  First, all
patterns in the group are the same, so they are not unordered, so CHECK
would have been sufficient.  Second, there's only one occurrence in the
actual output (which I'm assuming is correct), so there should be only one
directive, so it really doesn't matter which of these directives we use.

S5. Incorrect pattern with same match
-------------------------------------

For example, projects/compiler-rt/test/profile/instrprof-visibility.cpp has:

```
// COV-DAG: {{.*}}|{{ *}}1|#ifndef NO_WEAK
...
// COV-DAG: {{.*}}|{{ *}}1|#ifndef NO_WEAK
```

The "1" does not appear in first occurrence in the actual output. 
Let's
assume the actual output is correct and the first pattern is incorrect.  If
overlapping is permitted, the first pattern matches the intended line for
the second pattern, which quietly matches that line too.  If overlapping is
not permitted, FileCheck complains that the second pattern has nothing left
to match.

An example where the second pattern is incorrect:

* test/Bitcode/thinlto-summary-local-5.0.ll

An example where the incorrect pattern is identical but it's not as obvious
because a regex variable by a different name (ATOMIC_REDUCE_BARRIER_LOC
instead of REDUCTION_LOC) is captured within it:

* tools/clang/test/OpenMP/for_reduction_codegen_UDR.cpp has:

Path Forward
------------------

These examples seem like strong evidence that permitting overlapping
matches is a significant source of test errors.  Moreover, we have my
original goal that some test authors were apparently assuming was already
supported: to be able to handle sets of strings that are both unordered and
non-unique.  Nevertheless, it's possible that there are use cases, such as
the one suggested by S1, that we lose.

Here are some potential paths forward:

P1. Give up on approach #1 (non-overlapping CHECK-DAG) and go back to #2
(CHECK-DAG-N).  I don't prefer this, but it would be less work.

P2. Make CHECK-DAG non-overlapping but fix all test cases before committing
that change.  Patch reviews will surely be slow.

P3. Make non-overlapping CHECK-DAG a special mode that's off by default
until all test suites have been fixed.

By the way, I think it would be generally useful for FileCheck to have a
debugging mode that prints every match.  It would be particularly useful
while migrating to a non-overlapping CHECK-DAG.

Thoughts?

Joel


> --paulr
>
>
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I just stumbled across r332416, which was modifying a test with multiple
identical CHECK-DAG directives, which reminded me I needed to get back
to you about this... sorry for the slow response.
> From: Joel E. Denny [mailto:jdenny.ornl at gmail.com]
>> On Mon, May 7, 2018 at 12:56 PM, <paul.robinson at sony.com>
wrote:
>>> 1. In a CHECK-DAG group, don't let the matches for patterns
overlap.
>>> 2. Add a new CHECK-DAG-N directive, where N is some integer, to
express
>>> that a pattern must have N non-overlapping matches.
>>
>> I think #1 is much more intuitive and easy to describe/document than
#2.
>> Changing the meaning of DAG in that way is highly unlikely to affect
any
>> existing test, IMO.  And if it does, my first expectation is that the
test
>> wasn't doing what the author intended anyway.
>
> I implemented #1, and I now have 105 new unexpected tests failures from
> llvm core (58), clang (45), openmp runtime (1), and compiler-rt (1) test
> suites.
Okay... obviously more than I expected.  But hey, if we look at it as a
percentage of all tests, it's really small!  [attempting to salvage a
degree of self-respect]
> I've only looked at a few failures so far.  Of those, the problem is
> the expected one: in a CHECK-DAG group, multiple patterns match the
> same line, so not permitting overlapping matches causes some patterns
> never to match successfully.  However, all the overlapping matches so
> far seem unintentional.  That is, this new implementation seems to be
> catching test errors.
Awesome.  Catching test errors is a definite plus for the project.
> ...
> Path Forward
> ------------------
>
> These examples seem like strong evidence that permitting overlapping
> matches is a significant source of test errors.  Moreover, we have my
> original goal that some test authors were apparently assuming was
> already supported: to be able to handle sets of strings that are both
> unordered and non-unique.  Nevertheless, it's possible that there are
> use cases, such as the one suggested by S1, that we lose.
Hmmm... Either that one intended for the matches to be different, and
it's a bug that they aren't; or it's an overly flexible test, and 
tightening it up does no harm.  The test change to accommodate the
updated FileCheck behavior would have to go through the original test
author or some other domain expert in order to determine which it is.

I don't see the loss of flexibility as necessarily a bad thing; although
we might find cases where behavior reasonably varies across targets, and
then we would need to work out how to accommodate those differences.
> Here are some potential paths forward:
>
> P1. Give up on approach #1 (non-overlapping CHECK-DAG) and go back to
> #2 (CHECK-DAG-N).  I don't prefer this, but it would be less work.
>
> P2. Make CHECK-DAG non-overlapping but fix all test cases before
> committing that change.  Patch reviews will surely be slow.
>
> P3. Make non-overlapping CHECK-DAG a special mode that's off by default
> until all test suites have been fixed.
I vote for P3.  It's easier to divide up the work if the feature is in
upstream FileCheck, and it's easy for someone doing the work to enable
the feature in their local branch.  I would not bother making it a
command-line switch, unless we really do come up with cases where the
overlapping matches are absolutely the right solution for some class of
tests.

I suggest you file a bug with the complete list of test failures that
non-overlapping CHECK-DAG finds.  That will help keep track of the work,
and if anyone else feels moved to pick up some part of it, they can make
notes in the bug so we can try to avoid duplicating effort.  Hopefully
I can devote some time to this myself, I think it's how CHECK-DAG should
have been done in the first place and I'm sad we didn't catch it at the
time.
> By the way, I think it would be generally useful for FileCheck to have
> a debugging mode that prints every match.  It would be particularly
> useful while migrating to a non-overlapping CHECK-DAG.
>
> Thoughts?
>
> Joel
A debugging mode like that sounds like a useful feature for writing a
test, independent of the migration aid.  Do it.
 
--paulr

Paul Robinson <paul.robinson at sony.com> writes:
>> From: Joel E. Denny [mailto:jdenny.ornl at gmail.com]
>>> On Mon, May 7, 2018 at 12:56 PM, <paul.robinson at sony.com>
wrote:
>>>> 1. In a CHECK-DAG group, don't let the matches for patterns
overlap.
>>>> 2. Add a new CHECK-DAG-N directive, where N is some integer, to
express
>>>> that a pattern must have N non-overlapping matches.
>>>
>>> I think #1 is much more intuitive and easy to describe/document
than #2.
>>> Changing the meaning of DAG in that way is highly unlikely to
affect any
>>> existing test, IMO.  And if it does, my first expectation is that
the test
>>> wasn't doing what the author intended anyway.
>>
>> I implemented #1, and I now have 105 new unexpected tests failures from
>> llvm core (58), clang (45), openmp runtime (1), and compiler-rt (1)
test
>> suites.
...
>> Here are some potential paths forward:
>>
>> P1. Give up on approach #1 (non-overlapping CHECK-DAG) and go back to
>> #2 (CHECK-DAG-N).  I don't prefer this, but it would be less work.
>>
>> P2. Make CHECK-DAG non-overlapping but fix all test cases before
>> committing that change.  Patch reviews will surely be slow.
>>
>> P3. Make non-overlapping CHECK-DAG a special mode that's off by
default
>> until all test suites have been fixed.
>
> I vote for P3.  It's easier to divide up the work if the feature is in
> upstream FileCheck, and it's easy for someone doing the work to enable
> the feature in their local branch.  I would not bother making it a
> command-line switch, unless we really do come up with cases where the
> overlapping matches are absolutely the right solution for some class of
> tests.
I feel like a variant of this where this mode is on by default would
make more sense. That is,

1. Modify CHECK-DAG so that overlapping patterns aren't allow, unless
   --deprecated-allow-overlapping-check-dag or something is passed to
   FileCheck.
2. Add the flag to the 105 current test failures
3. File bugs and/or create reviews to remove the flag from each of the
   tests.

There are two reasons I prefer this approach. First, new tests are
"correct by default" while we clean up the existing problematic tests.
Second, out of tree work has an easy path forward and reasonable
forewarning. They can add the flag temporarily and fix problematic tests
when time permits, rather it suddenly breaking their CI whenever open
source flips the switch.
> I suggest you file a bug with the complete list of test failures that
> non-overlapping CHECK-DAG finds.  That will help keep track of the work,
> and if anyone else feels moved to pick up some part of it, they can make
> notes in the bug so we can try to avoid duplicating effort.  Hopefully
> I can devote some time to this myself, I think it's how CHECK-DAG
should
> have been done in the first place and I'm sad we didn't catch it at
the
> time.
>
>> By the way, I think it would be generally useful for FileCheck to have
>> a debugging mode that prints every match.  It would be particularly
>> useful while migrating to a non-overlapping CHECK-DAG.
>>
>> Thoughts?
>>
>> Joel
>
> A debugging mode like that sounds like a useful feature for writing a
> test, independent of the migration aid.  Do it.
+1

On Wed, May 16, 2018 at 11:40 AM, <paul.robinson at sony.com> wrote:
> I just stumbled across r332416, which was modifying a test with multiple
> identical CHECK-DAG directives, which reminded me I needed to get back
> to you about this... sorry for the slow response.
>
Not a problem.

> > From: Joel E. Denny [mailto:jdenny.ornl at gmail.com]
> >> On Mon, May 7, 2018 at 12:56 PM, <paul.robinson at sony.com>
wrote:
> >>> 1. In a CHECK-DAG group, don't let the matches for
patterns overlap.
> >>> 2. Add a new CHECK-DAG-N directive, where N is some integer,
to express
> >>> that a pattern must have N non-overlapping matches.
> >>
> >> I think #1 is much more intuitive and easy to describe/document
than #2.
> >> Changing the meaning of DAG in that way is highly unlikely to
affect
> any
> >> existing test, IMO.  And if it does, my first expectation is that
the
> test
> >> wasn't doing what the author intended anyway.
> >
> > I implemented #1, and I now have 105 new unexpected tests failures
from
> > llvm core (58), clang (45), openmp runtime (1), and compiler-rt (1)
test
> > suites.
>
> Okay... obviously more than I expected.  But hey, if we look at it as a
> percentage of all tests, it's really small!  [attempting to salvage a
> degree of self-respect]
>
I didn't exactly expect it either.  :-)
> I've only looked at a few failures so far.  Of those, the problem is
> > the expected one: in a CHECK-DAG group, multiple patterns match the
> > same line, so not permitting overlapping matches causes some patterns
> > never to match successfully.  However, all the overlapping matches so
> > far seem unintentional.  That is, this new implementation seems to be
> > catching test errors.
>
> Awesome.  Catching test errors is a definite plus for the project.
>
Thanks for encouraging me to pursue this implementation.

> > ...
> > Path Forward
> > ------------------
> >
> > These examples seem like strong evidence that permitting overlapping
> > matches is a significant source of test errors.  Moreover, we have my
> > original goal that some test authors were apparently assuming was
> > already supported: to be able to handle sets of strings that are both
> > unordered and non-unique.  Nevertheless, it's possible that there
are
> > use cases, such as the one suggested by S1, that we lose.
>
> Hmmm... Either that one intended for the matches to be different, and
> it's a bug that they aren't; or it's an overly flexible test,
and
> tightening it up does no harm.  The test change to accommodate the
> updated FileCheck behavior would have to go through the original test
> author or some other domain expert in order to determine which it is.
>
> I don't see the loss of flexibility as necessarily a bad thing;
although
> we might find cases where behavior reasonably varies across targets, and
> then we would need to work out how to accommodate those differences.
>
Agreed.

Thanks for the feedback.

Joel
> Here are some potential paths forward:
> >
> > P1. Give up on approach #1 (non-overlapping CHECK-DAG) and go back to
> > #2 (CHECK-DAG-N).  I don't prefer this, but it would be less work.
> >
> > P2. Make CHECK-DAG non-overlapping but fix all test cases before
> > committing that change.  Patch reviews will surely be slow.
> >
> > P3. Make non-overlapping CHECK-DAG a special mode that's off by
default
> > until all test suites have been fixed.
>
> I vote for P3.  It's easier to divide up the work if the feature is in
> upstream FileCheck, and it's easy for someone doing the work to enable
> the feature in their local branch.  I would not bother making it a
> command-line switch, unless we really do come up with cases where the
> overlapping matches are absolutely the right solution for some class of
> tests.
>
> I suggest you file a bug with the complete list of test failures that
> non-overlapping CHECK-DAG finds.  That will help keep track of the work,
> and if anyone else feels moved to pick up some part of it, they can make
> notes in the bug so we can try to avoid duplicating effort.  Hopefully
> I can devote some time to this myself, I think it's how CHECK-DAG
should
> have been done in the first place and I'm sad we didn't catch it at
the
> time.
>
> > By the way, I think it would be generally useful for FileCheck to have
> > a debugging mode that prints every match.  It would be particularly
> > useful while migrating to a non-overlapping CHECK-DAG.
> >
> > Thoughts?
> >
> > Joel
>
> A debugging mode like that sounds like a useful feature for writing a
> test, independent of the migration aid.  Do it.
>
> --paulr
>
>
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