llvm dev - Sep 2015 - AST of a program without any interference of semantic analyzer

Dear LLVMers,

I'm developing a tool to extract constraints from C programs. To do it, I
need, firstly, to be able to go over the Abstract Syntax Tree of a program.
Thus, I'm trying to use clang to get the AST of a program and start my
work from it. The problem that I'm having is that I don't know how I can
get the AST of a program without any intervention of the semantic analyzer.
I would like to analyze programs that have uses of undeclared variables.
However, once clang finds an undeclared variable, it stops building the
tree,
and just shows me the errors. If I need to modify clang, to continue
producing
the tree, e.g., assuming that every undeclared variable is extern, how can
I do it?

Or,  in other words, is there a way to disable the semantic analysis
and get the AST of a program without any interference of the this analyzer?

Since now, thank you very much!

Regards,
 Marcus
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(this conversation is more applicable to cfe-dev (cc'd) rather than
llvm-dev (please drop llvm-dev from further replies)

On Mon, Sep 14, 2015 at 12:34 PM, Marcus Rodrigues via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Dear LLVMers,
>
> I'm developing a tool to extract constraints from C programs. To do it,
I
> need, firstly, to be able to go over the Abstract Syntax Tree of a program.
> Thus, I'm trying to use clang to get the AST of a program and start my
> work from it. The problem that I'm having is that I don't know how
I can
> get the AST of a program without any intervention of the semantic
> analyzer.
> I would like to analyze programs that have uses of undeclared variables.
> However, once clang finds an undeclared variable, it stops building the
> tree,
> and just shows me the errors. If I need to modify clang, to continue
> producing
> the tree, e.g., assuming that every undeclared variable is extern, how can
> I do it?
>
> Or,  in other words, is there a way to disable the semantic analysis
> and get the AST of a program without any interference of the this analyzer?
>
Short answer: no. I suppose it might be supportable in C (we shuold produce
an AST, but we will produce errors (you can suppress them), with invalid
nodes for the variable references), it's certainly not supportable in C++
owing to the non-context-free nature of the C++ programming language.

- Dave

>
> Since now, thank you very much!
>
> Regards,
>  Marcus
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
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