[cfe-dev] AST Writer

Mon Jul 16 10:00:25 PDT 2018

I guess a few layers:

If you're going source-to-source and want users to see/modify the new
source, then making text edits based on source locations found in the AST
(but not modifying the AST itself) is generally the suggested idea. If you
simultaneously want to produce that source and compile it - yeah, probably
easier to write it out, then compile it from that source on the filesystem.

(there are probably some ways to compile from source in memory - but I'm
not sure of the details, it might involve using the virtual filesystem
layers - I think they were implemented for continuous compilation in IDEs
(compiling from the edited source buffers open in the editor without having
to write them to disk first))

On Fri, Jul 13, 2018 at 3:01 PM Matthieu Brucher <matthieu.brucher at gmail.com>
wrote:

> My domain would be electrical schema modeling. Some people would like to
> have the generated code, but then change one model of a component to
> something else. Or remove the Newton Raphson algorithm for another one. Or
> remove entries in the Jacobian matrix to check for terms that don't bring
> much to the result but could enhance performance.
> I could write the code in memory and then pass it to clang, but it
> feels... odd. But maybe that what I need to do in the end? In there an
> example of getting code from a  string?
>
> Cheers,
>
> Matthieu
>
> Le mar. 10 juil. 2018 à 23:17, David Blaikie <dblaikie at gmail.com> a
> écrit :
>
>>
>>
>> On Tue, Jul 10, 2018 at 2:49 PM Matthieu Brucher <
>> matthieu.brucher at gmail.com> wrote:
>>
>>> That's my use case, it's different than the OP, probably.
>>>
>>> In my case, I want to generate a first pass, with a JIT (the code is
>>> generated from another description), but the generated code could be
>>> changed by the user in a subsequent pass.
>>>
>>
>> Curious. As much as possible, I'd encourage you to find ways to not have
>> users work with generated code (by abstracting that generated code away
>> from them - giving them a higher level representation to write, places
>> where the generated code calls back into the user code, etc). But I don't
>> know your domain, etc, and wouldn't suggest what is or isn't right for you
>> and your users.
>>
>> But the main takeaway is that modifying the AST and generating code from
>> that is discouraged in favor of generating source code edits.
>>
>>
>>> Modifying directly the AST is not an option, try generating equations
>>> with thousands of parameters that are solved in real time. Just no way
>>> someone can write them efficiently in IR (that's why you have the AST to IR
>>> generator!).
>>>
>>> I don't understand your last paragraph. If clang-format can cleanup
>>> rewrites, why can't it reformat code from the AST? If the AST printer
>>> writes any kind of code, why couldn't clang-format reformat it?
>>>
>>
>> clang-format could format AST generated source too - I was commenting on
>> that in answer to your question "Easier to generate correctly formatted
>> code from the AST?" - that it's not easier to generate correctly formatted
>> code from the AST than it is from a textual edit. In both cases you'd use
>> something like clang-format to tidy up the result. The AST itself doesn't
>> have fancy formatting support so it's no better than a textual edit in
>> terms of getting nicely formatted results.
>>
>>
>>>
>>>
>>>
>>> Le mar. 10 juil. 2018 à 22:41, David Blaikie <dblaikie at gmail.com> a
>>> écrit :
>>>
>>>> Hmm, not sure I follow.
>>>>
>>>> Did the user write this source code? Are they going to want to change
>>>> it later? Does it make sense for them to see the edits you're suggesting,
>>>> or are those edits really compiler optimizations/transformations? If
>>>> they're more the latter, then perhaps caching the LLVM IR (with these
>>>> optimizations/transformations applied) rather than modifying the source
>>>> would be more suitable.
>>>>
>>>> Easier to generate correctly formatted code from the AST? Not really -
>>>> the AST printing doesn't have any particularly nuanced formatted printing.
>>>> That's what clang-format is for (it was specifically built for doing code
>>>> rewrites based on ASTs - where the rewrite is expressed as a textual change
>>>> to the original source (not an AST modification) & that change is applied,
>>>> then clang-format is used to tidy it up).
>>>>
>>>> On Tue, Jul 10, 2018 at 2:11 PM Matthieu Brucher <
>>>> matthieu.brucher at gmail.com> wrote:
>>>>
>>>>> It's odd though, because generating code on the fly would be easier on
>>>>> the AST than on the IR tree, if the goal is JIT and also saving the code at
>>>>> the same time.
>>>>> It's probably also easier also to generate properly formatted code?
>>>>>
>>>>> Regards,
>>>>>
>>>>> Matthieu
>>>>>
>>>>> Le mar. 10 juil. 2018 à 16:21, David Blaikie via cfe-dev <
>>>>> cfe-dev at lists.llvm.org> a écrit :
>>>>>
>>>>>> It's generally considered that the AST invariants are too
>>>>>> subtle/complex to use AST modification and AST->source conversion reliably.
>>>>>> Refactoring/source code modification is generally encouraged to be done via
>>>>>> textual edits generated from source location information in the AST.
>>>>>>
>>>>>> On Mon, Jul 9, 2018 at 8:36 PM Ridwan Shariffdeen via cfe-dev <
>>>>>> cfe-dev at lists.llvm.org> wrote:
>>>>>>
>>>>>>> Hi,
>>>>>>>
>>>>>>> I am trying to build a tool which can insert new AST nodes to a AST
>>>>>>> tree obtained from a source code and generate the modified source code. For
>>>>>>> example add an if condition to a given location.
>>>>>>>
>>>>>>> I have seen examples on ReWriter which can insert text, but I want
>>>>>>> to insert a proper AST node and generate the source code from the modified
>>>>>>> AST.
>>>>>>>
>>>>>>> For this purpose, I think I should be using ASTWriter and not
>>>>>>> ReWriter. Is there any documentation I can refer on how to implement this?
>>>>>>>
>>>>>>> Any help in this regard is highly appreciated.
>>>>>>>
>>>>>>> Thanks!
>>>>>>> Ridwan
>>>>>>> _______________________________________________
>>>>>>> cfe-dev mailing list
>>>>>>> cfe-dev at lists.llvm.org
>>>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>>>>>>>
>>>>>> _______________________________________________
>>>>>> cfe-dev mailing list
>>>>>> cfe-dev at lists.llvm.org
>>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Quantitative analyst, Ph.D.
>>>>> Blog: http://blog.audio-tk.com/
>>>>> LinkedIn: http://www.linkedin.com/in/matthieubrucher
>>>>>
>>>>
>>>
>>> --
>>> Quantitative analyst, Ph.D.
>>> Blog: http://blog.audio-tk.com/
>>> LinkedIn: http://www.linkedin.com/in/matthieubrucher
>>>
>>
>
> --
> Quantitative analyst, Ph.D.
> Blog: http://blog.audio-tk.com/
> LinkedIn: http://www.linkedin.com/in/matthieubrucher
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-dev/attachments/20180716/65f878e3/attachment.html>