[cfe-dev] AST Writer

David Blaikie via cfe-dev cfe-dev at lists.llvm.org
Tue Jul 10 14:41:18 PDT 2018

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>

> 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
>>> _______________________________________________
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>>> cfe-dev at lists.llvm.org
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> --
> Quantitative analyst, Ph.D.
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