[cfe-dev] AST Representation

[Manuel Klimek via cfe-dev]

I haven't looked too deeply into it, but from talking to various clang
developers, the common theme is disbelieve that a high-level C++ AST can be
created that is both useful and not overly specific to a single compiler.

>From the paper referenced in the project, I see multiple things that make
it seem not interesting to me from a point of refactoring and semantic
analysis:
- The IPR does not handle macros before their expansion in the preprocessor.
- does not mimic C++ language irregularities; general rules are used,
rather than long lists of special cases
- Unfortunately, a program cannot fully automate the generation of
“skeletons.” If our aim is portability, we still need to (by hand)
eliminate non-standard additions to the contents of header file.

Generally, I would not trust a representation that I can't generate code
from to be correct enough for tools.

On Wed, Feb 1, 2017 at 8:32 PM Reid Kleckner via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> Yes, the clang "abstract syntax tree" is often jokingly referred to as the
> "concrete syntax graph". We try to provide a generally useful
> representation, but being a fast production C++ compiler comes first.
> Clang's AST is very concrete. You have to know a lot about it to navigate
> it. There is no "Node" base class that you can use as a cursor to navigate
> around Decls, Exprs, Types, and TemplateArguments. Template instantiation,
> the closest thing I can think of to cloning, is done relatively manually
> with TreeTransform.
>
> I think it would be nice to revisit the design of clang's AST to simplify
> it, normalize it, and abstract it, but it is not a task to be taken
> lightly, and I don't expect it to happen in the near future.
>
> On Wed, Feb 1, 2017 at 8:44 AM, Gaetano Checinski via cfe-dev <
> cfe-dev at lists.llvm.org> wrote:
>
> As the AST is not really a Tree as it seems to have circular references,
> working with the AST is sometimes a bit messy (eg. cloning).
>
> A while ago Stroustroup pointed me to Gabriel Dos Reis' work on a
> different approach to represent C++-AST:
> https://github.com/GabrielDosReis/ipr
> <https://mailtrack.io/trace/link/a5c184fad2cf94fbf0449fa233263072ebc34ea8?url=https%3A%2F%2Fgithub.com%2FGabrielDosReis%2Fipr&signature=9a19f2a0a41d5ceb>
>
> Did anyone try to integrate his work into clang or has an opinion to share
> ?
>
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