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Re: [Tooling] std::compile

From: Rene Rivera <grafikrobot_at_[hidden]>
Date: Tue, 18 Sep 2018 21:41:29 -0500
On Tue, Sep 18, 2018 at 12:20 AM JF Bastien <cxx_at_[hidden]> wrote:

> On Mon, Sep 17, 2018 at 3:37 PM Rene Rivera <grafikrobot_at_[hidden]> wrote:
>> On Mon, Sep 17, 2018 at 5:04 PM JF Bastien <cxx_at_[hidden]> wrote:
>>> On Mon, Sep 17, 2018 at 1:38 PM Rene Rivera <grafikrobot_at_[hidden]>
>>> wrote:
>>>> On Mon, Sep 17, 2018 at 3:31 PM Tony V E <tvaneerd_at_[hidden]> wrote:
>>>>> Also, if you give me a function called std::compile(), that compiles
>>>>> code, it seems I can now write a compiler?
>>>>> int main(int argc, char ** argv)
>>>>> {
>>>>> return std::compile(argc, argv);
>>>>> }
>>>>> Wow, that was easy.
>>>>> Can the paper explain what I'm misunderstanding? (Or maybe it does
>>>>> explain, but I missed it)
>>>> That's a correct understanding. And that's the one example I use in my
>>>> implementation <
>>>> https://github.com/bfgroup/std_cpp/blob/master/example/std_cpp.cpp>. I
>>>> do try and explain the goals in the paper. In that it serves a dual
>>>> purpose. But mainly it's a way to standardize the compiler options.
>>> Right, otherwise you'd have to do:
>>> int main(int argc, char** argv) {
>>> std::system((std::string("clang ") + argv[1]).c_str());
>>> return 0;
>>> }
>>> ;-)
>>> More seriously, the selection of compiler options you've chosen seem
>>> semi-random.
>> First it's not random :-) It's the minimal to get basic actual compiling
>> working and to show highlight some of the differences in link
>> compatibility. Second, it's very incomplete. I'll keep adding options as I
>> implement them from now until the mailing deadline (and keep implementing
>> them afterwards for an R1 paper -- and so on). Third, I hope I can get some
>> volunteers to help in adding options.
>>> It would be useful to have a survey of existing compilers and their
>>> options, and some criteria to determine which should be supported here and
>>> which shouldn't.
>> Selection criteria is indeed a hard problem. What's actually needed for
>> core? And what can be delegated to the vendor specific realm?
> For context, I've added options in the past, removed some. It's not a big
> deal. It would be a big deal if the standard added and removed some. That's
> worrying.

Yes, it would be worrying. It might be the case that we need another level
of options defined: core options in the IS, common options in an SD, and
vendor options in SDs. Having the common options in an SD would allow for
the experience gathering lifetime like TSs do for library features.

Further, what's the expectation of the result of calling this function? Can
>>> I actually execute any code? How? Can you make sure that you take into
>>> account the restrictions various platforms have, such as requiring code
>>> authentication. It goes way beyond linkers.
>> The proposal doesn't, intentionally, say anything about executing code.
>> This is one of those "implementation defined" areas. Just like it is
>> currently in the standard. If it's possible to execute code in some manner,
>> either indirectly through an std::system equivalent or directly through
>> JIT/DLL, is left for the implementor/compiler to document.
> So a valid implementation always returns true, does nothing?

Yes. Returning "true" would get coerced to "1", since the function returns
an in. Which would indicate the error of not being implemented. Although
ideally it would also output an error message to that effect (if possible).

system seems like a precedent for what you suggest, and in my experience
>>> system isn't a precedent people want us to repeat.
>> "std::system" is what the sample implementation uses.. but it's possible
>> you could implement it as a direct library call (easily doable for Clang,
>> for example). And ideally production implementations would use something
>> more robust than std::system ;-)
> What's the upside of a library call?

One upside is that it's a known viable mechanism that can be standardized.
I also mention the in the paper runtime code compilation to target special
runtimes in the prior art (NVRTC). There's also the possibility of tighter
integration with build system to optimize build performance.

I get the impression you're going down a rabbit hole...
> How is the design different from something like this:
> https://clang.llvm.org/docs/DriverInternals.html
> ?

One similarity is that both compile source :-) Another, is of course, that
the clang driver (or front end) somewhat simulates the gcc front end. That
pattern is not uncommon.. I mention one of them in the prior art section.
Others are the various msvc compatible compilers, like Intel.

> Maybe the code will help explain what I have in mind:
> https://github.com/llvm-mirror/clang/blob/master/tools/driver/driver.cpp
> Or, put another way, why can't a Python script be used to frob
> command-line parameters in the way you propose?

It could. Although that would be a tool and as such not something we could
put into the IS.

> Have there been such tools in the past?

Sure. I mention clang-cl in the prior art section, for example. And if I
understand correctly Isabella Muerte is working on something like that
also. And some build systems do essentially the same job if they in any
form abstract the compiler options. That doesn't remove the desirability of
having a standard set of options and a library interface. In the contrary
it increases the desirability as there are obviously many instances of
duplicated effort that we could could help with while increases
interoperation of tools and build understanding of build products.

> Have they succeeded?

Some have.

> What were their approaches?

I think I already answered that.. in that they simulate another such tool.
Which helps in interoperation of their tool with others (i.e. being able to
substitute one compiler for another in an IDE or build system

How is this different from, say, how CMake does things? It tries to
> abstract away some flags and it does so much more than your proposal.

Not that different.. Although this would be more comprehensive and the
compiler vendors are in a better position to define their option

> Why would I want your proposal over CMake?

You would not choose it over CMake, or any other build system. But it would
make the build system much easier to implement. It would also make it
easier to use external libraries that use other build systems.

As I see it, the proposal is missing a bunch of context and related
> research. I'd like to see more to understand why it's the right tool for
> users of C++. I'm not convinced this tool needs to be usable from C++.

I will add more of the research and context as my time allows. Thanks for
the feedback. I hope you can also read the "Package Ecosystem Plan" paper
that has some of that context.

-- Rene Rivera
-- Grafik - Don't Assume Anything
-- Robot Dreams - http://robot-dreams.net

Received on 2018-09-19 04:41:42