[llvm-dev] [RFC] Compiled regression tests.

[Hal Finkel via llvm-dev]

On 7/1/20 11:13 AM, Michael Kruse wrote:
> Am Mi., 1. Juli 2020 um 09:33 Uhr schrieb Hal Finkel <hfinkel at anl.gov 
> <mailto:hfinkel at anl.gov>>:
>
>     I definitely agree that we should not be trying to do this kind of
>     checking using textual metadata-node matching in FileCheck. The
>     alternative already available is to add an analysis pass with some
>     kind of verifier output. This output, not the raw metadata itself,
>     can be checked by FileCheck. We also need to check the
>     verification code, but at least that's something we can keep just
>     in one place. For parallel annotations, we already have such a
>     thing (we can run opt -loops -analyze; e.g., in
>     test/Analysis/LoopInfo/annotated-parallel-complex.ll). We also do
>     this kind of thing for the cost model (by running with -cost-model
>     -analyze). To what extent would making more-extensive use of this
>     technique address the use cases you're trying to address?
>
> The CHECK lines in annotated-parallel-complex.ll are:
>
> ; CHECK: Parallel Loop at depth 1
> ; CHECK-NOT: Parallel
> ; CHECK:     Loop at depth 2
> ; CHECK:         Parallel Loop
> ; CHECK:             Parallel Loop
>
> When adding this test, I had to change LoopInfo to emit the "Parallel" 
> in front of "Loop". For readability, I would have preferred the 
> parallel info as a "tag", such as `Loop (parallel) as depth 1`, but 
> this would break other tests that check "Loop at depth 1". Later I 
> noticed that there are regression tests that check "LoopFullUnrollPass 
> on Loop at depth 3 containing: %l0.0.0<header>", but it seems I got 
> lucky in that none of these loops have parallel annotations.
>
> "CHECK-NOT" is inherently fragile. It is too easy to make a change in 
> LLVM that changes the text output and oversee that this test does not 
> check what it was supposed to test. For a FileCheck-friendlier output, 
> it could emit "NonParallel" and match this. However, this clutters the 
> output for humans, will actually break the "LoopFullUnrollPass on Loop 
> at depth 3 ..." and "CHECK: Parallel" matches this as well since 
> FileCheck ignores word boundaries.
>
> The CHECK lines test more than necessary. The first and third CHECK 
> lines also check the "at depth" to make it match the correct loop (and 
> not, e.g. match the next inner loop), although we are not interested 
> in the loop depths themselves. Ironically, is the reason why cannot be 
> tags between "Loop" and "at depth"


We can have different printing modes. There can be a more-human-friendly 
mode and a more-FileCheck-friendly mode. Or modes customized for 
different kinds of tests. I agree, however, that this does not solve the 
fragility problems with CHECK-NOT.


>
> Not all of the loop metadata have passes that print them. For 
> instance, there are loop properties such as llvm.loop.isvectorized. 
> Reading those is usually done using utility functions such as 
> getBooleanLoopAttribute(L, "llvm.loop.isvectorized"). A solution using 
> FileCheck would be to add another pass that prints loop metadata. That 
> pass would only be used for testing, making the release LLVM binaries 
> larger than necessary and still have the other problems.
>
> Processing the IR through a tool can make the output more 
> FileCheck-friendly, but it doesn't make its problems disappear. IMHO 
> it adds to the maintenance burden since it adds more textual interfaces.


That's the interesting question... it does add to the maintenance 
burden. However, having textual outputs are also quite convenient when 
debugging things (because I can change the input and see the output 
quickly, without needing to create and compile another program). 
Obviously, at some point, this becomes ridiculous. How much is too much? 
I don't know. But it's also not clear to me that we're at that point 
yet. We could add more textual analysis outputs and still have that be a 
net benefit in many places.

In cases where the requisite output would just be too specific, we do 
have unit tests. Should we just add more? Maybe we're too happy to add 
lit tests instead of unit tests for some of these cases.


>
> Michael
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-- 
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory

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