[cfe-dev] AST Writer

Matthieu Brucher via cfe-dev cfe-dev at lists.llvm.org
Tue Jul 17 11:08:44 PDT 2018


Hi,

I can easily add source code to a file. It's a no brainer, I'm not going to
use clang for this, it's overkill.
What doesn't work, as stated in my previous example, is getting a module
out of clang, a module that can be used inside llvm. When executing the
code below, I get a write error. That's a problem because there are no
resources online on this issue. The api changes too quickly for this, and
even lib clang doesn't help because then the triple is not set (and then
llvm breaks).

Cheers
Matthieu

Le mar. 17 juil. 2018 à 18:25, Firat Kasmis <firatkasmis at gmail.com> a
écrit :

> Matthieu, try https://github.com/firolino/clang-tool as getting started
> and change the transformer to your needs to insert code/text at a given
> location. Hope it helps.
>
> Best,
> Firat
>
> Am Di., 17. Juli 2018 um 09:00 Uhr schrieb Matthieu Brucher via cfe-dev <
> cfe-dev at lists.llvm.org>:
>
>> Indeed, that's what I'm now aiming at. Unfortunately, it seems that there
>> are no examples as how to use FrontEndAction properly with clang 6.0.0. I
>> can use libeling with runToolOnCode to generate a module, but the triple is
>> not set up properly in that case when I want to use the JIT. And it seems
>> to be a problem with clang, as if I do this:
>>
>>     clang::DiagnosticOptions diagnosticOptions;
>>     std::unique_ptr<clang::TextDiagnosticPrinter> textDiagnosticPrinter =
>>       std::make_unique<clang::TextDiagnosticPrinter>(llvm::outs(),
>>                                                      &diagnosticOptions);
>>     llvm::IntrusiveRefCntPtr<clang::DiagnosticIDs> diagIDs;
>>
>>     std::unique_ptr<clang::DiagnosticsEngine> diagnosticsEngine =
>>       std::make_unique<clang::DiagnosticsEngine>(diagIDs, &diagnosticOptions, textDiagnosticPrinter.get());
>>
>>     clang::LangOptions languageOptions;
>>     clang::FileSystemOptions fileSystemOptions;
>>     clang::FileManager fileManager(fileSystemOptions);
>>     clang::SourceManager sourceManager(*diagnosticsEngine,
>>                                        fileManager);
>>     std::shared_ptr<clang::HeaderSearchOptions> headerSearchOptions(new clang::HeaderSearchOptions());
>>
>>     const std::shared_ptr<clang::TargetOptions> targetOptions = std::make_shared<clang::TargetOptions>();
>>     targetOptions->Triple = llvm::sys::getDefaultTargetTriple();
>>
>>     std::unique_ptr<clang::TargetInfo> targetInfo(
>>       clang::TargetInfo::CreateTargetInfo(*diagnosticsEngine, targetOptions));
>>
>>     clang::HeaderSearch headerSearch(headerSearchOptions,
>>                                      sourceManager,
>>                                      *diagnosticsEngine,
>>                                      languageOptions,
>>                                      targetInfo.get());
>>     clang::MemoryBufferCache PCMCache;
>>     clang::CompilerInstance compInst;
>>
>>     std::shared_ptr<clang::PreprocessorOptions> opts(std::make_shared<clang::PreprocessorOptions>());
>>     clang::Preprocessor preprocessor(opts,
>>                                      *diagnosticsEngine,
>>                                      languageOptions,
>>                                      sourceManager,
>>                                      PCMCache,
>>                                      headerSearch,
>>                                      compInst);
>>     preprocessor.Initialize(*targetInfo);
>>
>>     auto filter = llvm::MemoryBuffer::getMemBufferCopy(fullfile);
>>
>>     sourceManager.setMainFileID(sourceManager.createFileID(std::move(filter)));
>>
>>     clang::IdentifierTable identifierTable(languageOptions);
>>     clang::SelectorTable selectorTable;
>>
>>     clang::Builtin::Context builtinContext;
>>     builtinContext.InitializeTarget(*targetInfo, nullptr);
>>     clang::ASTContext astContext(languageOptions,
>>                                  sourceManager,
>>                                  identifierTable,
>>                                  selectorTable,
>>                                  builtinContext);
>>     astContext.InitBuiltinTypes(*targetInfo);
>>     compInst.setTarget(targetInfo.get());
>>
>>     llvm::LLVMContext context;
>>     std::unique_ptr<clang::CodeGenAction> action = std::make_unique<clang::EmitLLVMAction>(&context);
>>
>>     textDiagnosticPrinter->BeginSourceFile(languageOptions, &preprocessor);
>>
>>     compInst.ExecuteAction(*action);
>>
>>
>> Then inside the action, even if I created the TargetInfo myself, clang
>> tries something nasty:
>>
>> ASAN:DEADLYSIGNAL
>>
>> =================================================================
>>
>> ==25220==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000120
>> (pc 0x00010e786a2b bp 0x7ffee23ffda0 sp 0x7ffee23ffcc0 T0)
>>
>> ==25220==The signal is caused by a WRITE memory access.
>>
>> ==25220==Hint: address points to the zero page.
>>
>>     #0 0x10e786a2a in
>> clang::TargetInfo::CreateTargetInfo(clang::DiagnosticsEngine&,
>> std::__1::shared_ptr<clang::TargetOptions> const&)
>> (libATKModelling.dylib:x86_64+0xf19a2a)
>>
>>     #1 0x10ea7559b in
>> clang::CompilerInstance::ExecuteAction(clang::FrontendAction&)
>> (libATKModelling.dylib:x86_64+0x120859b)
>>
>> Cheers,
>>
>> Matthieu
>>
>> Le lun. 16 juil. 2018 à 18:00, David Blaikie <dblaikie at gmail.com> a
>> écrit :
>>
>>> 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
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>>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> --
>>>>>>>> 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
>>>>
>>>
>>
>> --
>> Quantitative analyst, Ph.D.
>> Blog: http://blog.audio-tk.com/
>> LinkedIn: http://www.linkedin.com/in/matthieubrucher
>> _______________________________________________
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>
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