[LLVMdev] [RFC] Internal command line options should not be statically initialized.

[Andrew Trick]

On Sep 18, 2013, at 8:58 AM, Chris Lattner <clattner at apple.com> wrote:

> On Sep 17, 2013, at 10:10 AM, Andrew Trick <atrick at apple.com> wrote:
>> LLVM's internal command line library needs to evolve. We have an immediate need to build LLVM as a library free of static initializers, but before brute-force fixing this problem, I'd like outline the incremental steps that will lead to a desirable long term solution. We want infrastructure in place to provide an evolutionary path.
> 
> Thank you for tackling this, we should have fixed this years ago.
> 
> Please do a pass over the cl::opts we have, and remove ones that are long dead or unused.   Do we still need -join-liveintervals? :-)
> 
> 
> On Sep 17, 2013, at 12:03 PM, Daniel Dunbar <daniel at zuster.org> wrote:
>> On Tue, Sep 17, 2013 at 11:29 AM, Reid Kleckner <rnk at google.com> wrote:
>> Wait, I have a terrible idea.  Why don't we roll our own .init_array style appending section?  I think we can make this work for all toolchains we support.
>> 
>> Andy and I talked about this, but I don't think its worth it. My opinion is:
>> 1. For tool options (the top-level llc, opt, llvm-as etc. opts) it doesn't matter.
>> 2. For experimental options (options that we would be happy if they were compiled out of a production compiler/JIT client/whatever), it doesn't matter.
>> 3. For backend options that need to always be available, lots of them probably already need to get promoted to real API.
>> 4. For the remaining options (ones that don't need to become API, but also aren't purely experimental), many of them can probably easily be initialized by some existing initialization hook (pass initialization, target initialization).
>> 5. There aren't enough options left not in those categories to motivate some kind of clever solution.
> 
> I think that this is a great summary of the problem.  Having cl::opt's compiled *out* of non-assert build by default makes a lot of sense to me, and having tool options use toolopt<> (or something) also makes perfect sense.
> 
> If you're going to go and tackle pass-specific options, I think that we should consider changing the syntax and overall design of the command line options.   We already have some manual name mangling/namespacification of options (e.g. -tail-dup-limit=). Perhaps we should formalize this somehow?

Obviously, based on the 18 responses I've gotten, the tone of my first email was misleading.

I don’t want to stifle discussion, but to be clear, the only thing I propose to tackle immediately is the removal of static initializers from libraries. There are several isolated issues that Filip has found good workarounds for. cl::opt is the one pervasive problem that can't be weeded out one case at a time.

The purpose of posting an RFC and opening up discussion was to find out from people who have already thought about this, how the ideal cl::opt framework should work. I won't be making that happen, rather I'll make sure that the changes we make don't get in the way of future progress.

I would certainly love to see LLVM internal options be reorganized and help however I can, but I'll be very sad if that holds up removing static initializers.

-Andy
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