[cfe-dev] Student of prof. Reichenbach with questions on clang ast

Manuel Klimek klimek at google.com
Thu Jan 23 07:10:28 PST 2014

On Thu, Jan 23, 2014 at 4:03 PM, Krishna Narasimhan
<krishna.nm86 at gmail.com>wrote:

> Thanks a lot Klimek,
> The reason I primarily wanted an AST transformation was the inherent
> issues with co dependent multiple transformations.
> For eg, lets say there is a node A which i just transformed and a
> predecessor node B which needs to be transformed based on the transformed
> version of A, i might need to include that transformed A node somewhere or
> flag it appropriately right?

Well, generally, changing the AST and re-running an analysis over the AST,
or changing the source code, re-parsing the AST, and then re-running an
analysis should be equivalent in expressiveness.

> I will look into that issue
> About the macros. Are there any specific code locations I could look at to
> get this preprocessed token streams to make sense of the macros?

Look at SourceLocations, which can be resolved via the SourceManager.


> P.S: I have included the clang mailing list.  :-)
> ---------- Forwarded message ----------
> From: Manuel Klimek <klimek at google.com>
> Date: Thu, Jan 23, 2014 at 1:12 PM
> Subject: Re: Student of prof. Reichenbach with questions on clang ast
> To: Krishna Narasimhan <krishna.nm86 at gmail.com>
> On Thu, Jan 23, 2014 at 1:08 PM, Krishna Narasimhan <
> krishna.nm86 at gmail.com> wrote:
>> Hi, I am a student of Prof. Dr. Reichenbach .
>> I have two questions regarding Clang(which I plan to use for my
>> transformations):
>> 1) How do i perform a transformation on the AST. I see that it is
>> immutable. Are there support in Clang for this or external tools?
> Nope. It's hard to change a C++ AST in a way that doesn't break its
> invariants. What we prefer to do (and for which tools exist) is to use the
> AST to figure out which code to change, and then change the code
> (textually). Clang has very good support for finding out what code models
> which part of the AST.
>> 2) Is there a way to prevent the pre processing (or rather) a way to
>> modify an AST that is not the pre processed version of the program. For eg,
>> if i want to refactor a #define, i currently have no way. Or?
> Again, no. But Clang's preprocessed token stream has all information to
> see how macros are expanded, so you *can* refactor a #define.
> In general, I'd suggest you always include clang's developer mailing list
> (cfe-dev) when asking such questions, as they're often interesting for
> other people ;)
> Cheers,
> /Manuel
> --
> -----------------------------------------------------
> I dare do all that may become a man; Who dares do more, is none - Macbeth,
> twelfh night!
> Regards
>        KrishnaThanks
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