[llvm-dev] Is there precedent for customizing clang -help output in a toolchain specific way

[Snider, Todd via llvm-dev]

Hi Andrzej,

I've been playing around with a couple of approaches to allow a toolchain to take control of the content of the -help output, but I'm not thrilled with the results.

The general approach that I've tried is to have a toolchain-specific version of PrintHelp() create its own OptTable either by filtering the OptTable generated from Options.td or by using a toolchain-specific version of Options.td that contains only the options and HelpText fields that the toolchain wants in the -help output. Each of these approaches has to mess with a generic API in some way (either the OptTable API or the Driver API).

Have you had some success in your attempts to customize Driver::PrintHelp()? I'd be interested to learn what you've tried.

~ Todd

-----Original Message-----
From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of Andrzej Warzynski via llvm-dev
Sent: Monday, July 27, 2020 3:53 AM
To: llvm-dev at lists.llvm.org; 'cfe-dev at lists.llvm.org'
Subject: [EXTERNAL] Re: [llvm-dev] Is there precedent for customizing clang -help output in a toolchain specific way

[+ cfe-dev]

Hi Todd,

We're currently trying to solve a similar problem for Flang [1]. From 
what we have seen so far,

* Options.td
* the only instance of DriverOptTable [2]
* the ID enum from clang/include/clang/Driver/Options.h [3]

are tightly coupled together and hence it is tricky to pick and choose 
what you want.

There's also getIncludeExcludeOptionFlagMasks in 
clang/lib/Driver/Driver.cpp [4], but I'm confused about the meaning of 
IncludedFlagsBitmask and ExcludedFlagsBitmask. We did experiment with 
that, but that made libclangDriver quite unhappy (things started to 
break in an unexpected way).

Perhaps somebody on cfe-dev (CC'ed) would have some hints? In the 
meantime we've also been customising Driver::PrintHelp().

-Andrzej


[1] http://lists.llvm.org/pipermail/llvm-dev/2020-June/141994.html
[2] 
https://github.com/llvm/llvm-project/blob/2c1799f8928e1a63020fa8099d254c084f8be2f2/clang/lib/Driver/DriverOptions.cpp#L43
[3] 
https://github.com/llvm/llvm-project/blob/2c1799f8928e1a63020fa8099d254c084f8be2f2/clang/include/clang/Driver/Options.h#L39
[4] 
https://github.com/llvm/llvm-project/blob/2c1799f8928e1a63020fa8099d254c084f8be2f2/clang/include/clang/Driver/Options.h#L26


On 24/07/2020 20:36, Snider, Todd via llvm-dev wrote:
> Hi All,
> 
> I am looking to customize the -help display for a downstream clang port 
> as many options defined in Options.td are not applicable to the 
> processor family I�m targeting and several applicable options do not 
> have HelpText.
> 
> I�ve considered adding a toolchain specific hook in the vicinity of 
> Driver::PrintHelp(), but I�d rather avoid adding a hook if there is a 
> better solution that already exists.
> 
> Is there a best practice for enabling a toolchain to control the output 
> of the clang �help option?
> 
> ~ Todd Snider
> 
> 
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> 
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