[cfe-dev] [llvm-dev] AST of a program without any interference of semantic analyzer

David Blaikie via cfe-dev cfe-dev at lists.llvm.org
Mon Sep 14 13:08:49 PDT 2015

(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
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