[llvm-dev] Multiple documents in one test file

[Pavel Labath via llvm-dev]

On 14/07/2020 03:27, David Blaikie via llvm-dev wrote:
> (+Richard - it's handy to include folks from previous discussions
> explicitly so everyone can more easily keep track of the conversation)
> 
> On Mon, Jul 13, 2020 at 6:17 PM Fangrui Song via llvm-dev
> <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
> 
>     Sometimes it is convenient if we can specify multiple independent tests
>     in one file. To give an example, let's discuss
>     test/MC/ELF/debug-md5.s and
>     test/MC/ELF/debug-md5-err.s (.file directive in the assembler).
> 
>     a) An invalid .file makes the whole file invalid. Because errors
>     lead to a
>     non-zero exit code, We have to use `RUN: not llvm-mc %s` for the
>     whole file.
>     This often lead to users placing good (`RUN: llvm-mc %s`) and bad
>     tests (`RUN:
>     not llvm-mc %s`) separately. For some features, having both good and
>     bad tests
>     in one file may improve readability.
>     b) .debug_line is a global resource. Whenever we add a (valid) .file, we
>     contribute an entry to the global resource. If we want to test some
>     characteristics when include_directories[0] is A, and other
>     characteristics
>     when include_directories[0] is B, we have to use another test file.
> 
>     The arguments apply to many other types of tests (opt on .ll, llc on
>     .ll and .mir, clang on .c, yaml2obj on .yaml, etc).
> 
>     I have a patch teaching llvm-mc about an option to split input:
>     https://reviews.llvm.org/D83725
>     (30+ lines)
> 
>     In a comment, Richard Smith mentioned whether we can add a separate
>     extractor utility:
> 
>     ```
>     # RUN: extract bb %s | llvm-mc - 2>&1 | FileCheck %s --check-prefix=BB
> 
>     or
> 
>     # RUN: extract bb %s -o %t.bb <http://t.bb>
>     # RUN: llvm-mc %t.bb <http://t.bb> 2>&1 | FileCheck %t.bb <http://t.bb>
>     ```
> 
> 
> Could make "extract" work a bit like "tee" so it can still be one line:
> 
> # RUN: extract bb %s -o %t.bb <http://t.bb> | llvm-mc - 2>&1 | FileCheck
> %t.bb <http://t.bb>
> 
> (could even make it a bit shorter for convenience - 'ex' or something)
>  
> 
>     The advantage is its versatility. The downside is somewhat verbose
>     syntax.
> 
> 
>     Some questoms:
> 
>     1. What do people think of the two approaches? An in-utility option
>     vs a standalone utility.
>     2. For llvm-mc, if we go with an option, is there a better name than
>     --doc-id? David Blaikie proposed --asm-id
>        (This is my personal preference, trading 30+ lines in a utility
>     for simpler syntax)

FWIW, the way I've done this in llvm-mc so far is via a combination of
"--defsym CASE<N>" command line argument and ".ifdef" asm directives.
This has the advantage that individual "documents" don't need to be
fully standalone (though they can be), so you can put the common parts
of the tests into an unconditionally compiled block.

That said, I was using this technique for constructing test cases for
other tools via llvm-mc. Things might get a bit awkward if you try to
test .ifdef processing itself this way...

pl