[llvm-dev] Making llvm-xyz -help useful

[James Henderson via llvm-dev]

Hi Serge,

I'm all for any approach that hides irrelevant options from the individual
tools. This is one method. Another method might be to switch to using
tablegen, like we do with LLD or llvm-objcopy, which will have other
benefits too relating to command-line option handling. However, it is
important that we don't lose options that ARE relevant to the tool by any
such switch. I cannot comment on which options those are for some tools,
but at least for the tools that I've been working on recently, I'm happy to
review (and indeed have done for some in the past).

James

On Thu, 9 May 2019 at 17:24, Serge Guelton via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hi folks,
>
> today, I wanted to concatenate two .ll, and naively typed:
>
>     $ llvm-cat -help
>
> This is the not-so-helpful output I had:
>
>     OVERVIEW: Module concatenation
>     USAGE: llvm-cat [options] <input  files>
>
>     OPTIONS:
>
>     General options:
>
>       -aarch64-neon-syntax                              - Choose style of
> NEON code to emit from AArch64 backend:
>         =generic                                        -   Emit generic
> NEON assembly
>         =apple                                          -   Emit
> Apple-style NEON assembly
>       -amdgpu-dump-hsa-metadata                         - Dump AMDGPU HSA
> Metadata
>       -amdgpu-enable-merge-m0                           - Merge and hoist
> M0 initializations
>       -amdgpu-sdwa-peephole                             - Enable SDWA
> peepholer
>     [...]
>
> Surely, the style of NEON code to emit from AArch64 backend is not the
> information I was looking for...
>
> I've implemented a straight-forward patch for llvm-cat here
> https://reviews.llvm.org/D61740, and the result becomes:
>
>     OVERVIEW: Module concatenation
>     USAGE: llvm-cat [options] <input  files>
>
>     OPTIONS:
>
>     Generic Options:
>
>       --help        - Display available options (--help-hidden for more)
>       --help-list   - Display list of available options
> (--help-list-hidden for more)
>       --version     - Display the version of this program
>
>     llvm-cat Options:
>
>       -b            - Whether to perform binary concatenation
>       -o=<filename> - Output filename
>
>
> Depending on the tools, the filtering imposed by
> llvm::cl::HideUnrelatedOptions may be too harsh, but there's still
> -help-hidden for the curious!
>
> Any thoughts on that approach? Should I go on that way for other tools? If
> so, anyone willing to be auto-added as a reviewer?
>
> ++
> Serge
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