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

[Joel E. Denny via llvm-dev]

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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