[llvm-dev] FileCheck idiom difficulties

Thomas Preud'homme via llvm-dev llvm-dev at lists.llvm.org
Wed Nov 6 05:54:18 PST 2019

Aren't the name lines unique? If they are you could use the good old CHECK-LABEL:

# CHECK-LABEL: Name: foo
# CHECK: Section: .foo (1)
From: George Rimar <grimar at accesssoftek.com>
Sent: 06 November 2019 13:01
To: jh7370.2008 at my.bristol.ac.uk <jh7370.2008 at my.bristol.ac.uk>
Cc: Fāng-ruì Sòng <maskray at google.com>; llvm-dev <llvm-dev at lists.llvm.org>; Thomas Preud'homme <thomasp at graphcore.ai>; Paul Robinson <paul.robinson at sony.com>
Subject: Re: FileCheck idiom difficulties

> One idea I had was for a new directive something like "CHECK-IMMEDIATE" which

> is implicitly the same as the final approach I suggested above, but maybe adding a new

> directive to achieve this isn't the right approach?

"CHECK-IMMEDIATE"​ (or "CHECK-CONTINUE"/better name) sound like a clean and fine approach to me.

​I'd go with it probably.

Best regards,
George | Developer | Access Softek, Inc
От: James Henderson <jh7370.2008 at my.bristol.ac.uk>
Отправлено: 6 ноября 2019 г. 15:17
Кому: llvm-dev; George Rimar; Fāng-ruì Sòng; Paul Robinson; thomasp at graphcore.ai
Тема: FileCheck idiom difficulties

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Hi all,

Many of our lit tests use FileCheck and a tool like llvm-readobj to check properties of a section header/symbol/etc. A typical (pseudoised for brevity) output to match against might be something like the following:

Symbols [
  Symbol {
    Name: foo
    Value: 0
    Type: Function
    Section: .foo (1)
  Symbol {
    Name: bar
    Value: 1
    Type: Object
    Section: .foo (1)

and your lit test might want to check the properties of the foo symbol like so:

# CHECK:      Name: foo
# CHECK-NEXT: Value: 0
# CHECK-NEXT: Type: Function
# CHECK-NEXT: Section: .foo (1)

This is fine. But what if you only care about the section of a symbol, and not the value or type etc? You could do the following:

# CHECK: Name: foo
# CHECK: Section: .foo (1)

Hopefully some of you will already notice the problem with this approach: if foo was in, say, the .baz section, the test will spuriously pass, because the Section line will match the Section line for .bar. One alternative to this is to explicitly match each field in between, using CHECK-NEXT:

# CHECK:      Name: foo
# CHECK-NEXT: Value:
# CHECK-NEXT: Section: .foo (1)

This works, but somewhat hides what is really being tested by adding extra noise to the checks. In reality, there are actually other fields too that need to be listed, meaning the "interesting" parts of the test are even more hidden.

I recently started using yet another approach:

# CHECK: Name: foo
# CHECK: Section:
# CHECK-SAME:     .foo (1)

This works because the Section: matched will be the first one found, i.e. the one belonging to foo, and then .foo will be looked for on the same line. However, I noticed today that this pattern has its own problem, namely that there could be something between the Section tag and .foo. In other words, the above pattern would match "Section: .bar.foo". A couple of solutions to this are:

# CHECK: Section:
# CHECK-NOT: {{[:graph:]}}
# CHECK-SAME: .foo (1)

# CHECK: Section:
# CHECK-SAME: {{^}} .foo (1)

The first one ensures that there's no non-whitespace between the end of "Section:" and the start of ".foo (1)". The second ensures that the start of the CHECK-SAME match is the "start of line", and since the first half of the line has already been consumed, it means " .foo (1)" must immediately follow "Section:". However, the first is even less readable than the current CHECK-SAME approach, whilst the second is somewhat confusing if you don't realise that FileCheck effectively consumes the things it has matched already, so that they effectively don't exist any more.

Does anybody have any other suggestions/thoughts/comments? One idea I had was for a new directive something like "CHECK-IMMEDIATE" which is implicitly the same as the final approach I suggested above, but maybe adding a new directive to achieve this isn't the right approach?


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