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

[Jessica Paquette via llvm-dev]

I would personally like a feature like that in FileCheck because it would make it a lot easier to write MachineOutliner tests, and would make the tests significantly smaller and easier to understand.

- Jessica

> On May 4, 2018, at 8:40 AM, Joel E. Denny via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> Hi,
> 
> Using FileCheck, I have not found a way to make a group of CHECK-DAG directives match multiple occurrences of a string.  For example, I naively thought the following would match successfully:
> 
> ```
> $ cat checks.txt 
> // CHECK: start
> // CHECK-DAG: foo
> // CHECK-DAG: foo
> // CHECK-DAG: bar
> // CHECK-NEXT: end
> 
> $ cat input.txt 
> start
> foo
> bar
> foo
> end
> 
> $ FileCheck --input-file=input.txt checks.txt
> checks.txt:5:16: error: CHECK-NEXT: is not on the line after the previous match
> // CHECK-NEXT: end
>                ^
> input.txt:5:1: note: 'next' match was here
> end
> ^
> input.txt:3:4: note: previous match ended here
> bar
>    ^
> input.txt:4:1: note: non-matching line after previous match is here
> foo
> ^
> ```
> 
> The trouble is that both "CHECK-DAG: foo" directives match the first "foo".
> 
> I'd like this ability for testing a parallel program that outputs a series of non-unique strings in non-deterministic order.  Am I trying to push FileCheck beyond its intended domain?  Is there some existing feature for this purpose that I've overlooked?  If not, I see two potential solutions:
> 
> 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.
> 
> An advantage of #1 that the intuitive way (at least in my mind) of expressing multiple occurrences of a string, as in the example above, would work.  An advantage of #2 is that existing CHECK-DAG functionality would not change, and so there should be no chance of impacting existing well formed tests.
> 
> To understand the issue better, I've prototyped #2.  It still needs test cases and documentation, so it's not ready for a formal patch review.  If people like the idea, I'll polish it up.
> 
> Thanks.
> 
> Joel
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