[cfe-dev] Patch: AST Matcher Framwork and an example tool

[Manuel Klimek]

Ping?

On Thu, Jun 2, 2011 at 10:32 AM, Manuel Klimek <klimek at google.com> wrote:

> +cfe-dev, -cfe-commits
>
> As requested by Chris I have reverted the Tooling stuff, and am bumping
> this thread on cfe-dev.
>
> Please find the original mail proposing the patch sent to cfe-commits on
> May 23rd inlined below.
>
> References to the original threads:
> Proposal:
> http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20110523/042163.html
> Commit:
> http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20110530/042375.html
>
> Patches produced by the example tool sent out (has not got feedback yet):
> Clang:
> http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20110523/042212.html
> LLVM:
> http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20110523/121387.html
>
> More context on why this is useful: when writing code transformation tools
> to do large scale changes on libraries with clang, we noticed that a lot of
> the code we wrote was "unrolled" matching of tree structures on the AST,
> which required a lot of dynamic casting and deeply nested control flow
> structures.
> The library we implemented based on those findings allows a very
> declarative way of expressing interesting parts of the AST that you want to
> work on, with a callback mechanism to have an imperative part that does the
> actual transformation. The way this library uses templates to build up a
> reverse hierarchy of the clang AST allows us to expand the library of
> matchers without needing to manually copy the structure of the AST while
> still providing full compile time type checking.
> We have used this library for many internal transformations (one more
> broadly applicable of them being included as an example tool), and Nico may
> be able to explain more how he's using the infrastructure for Chromium.
>
> The future work (as outlined to some extend in the original email) is to
> build up code transformation tools (including the standard refactoring tools
> we know from other languages) and libraries to make it easy for developers
> to contribute both generally useful tools and make it easy to write one-off
> tools for cleanup transformations on larger code bases.
>
> I would love this to be part of clang mainline, as the expertise and
> feedback of the community has been very helpful and valuable.
>
> ---------- Forwarded message ----------
> From: Manuel Klimek <klimek at google.com>
> Date: Mon, May 23, 2011 at 3:03 PM
> Subject: Patch: AST Matcher Framwork and an example tool
> To: cfe-commits at cs.uiuc.edu
> Cc: Nico Weber <thakis at chromium.org>, Marcin Kowalczyk <qrczak at google.com>,
> James Dennett <jdennett at google.com>
>
>
> This patch implements an AST matching framework that allows to write tools
> that match on the C++ ASTs. The main interface is in ASTMatchers.h, an
> example implementation of a tool that removes redundant .c_str() calls is in
> the example RemoveCStrCalls.cpp (patch to llvm/clang produced by running
> this tool will be sent out shortly in an extra email).
>
> Currently we have an in-language DSL that allows to write expressions such
> as (taken from the .c_str() example):
> ConstructorCall( HasDeclaration(Method(HasName(StringConstructor))), ArgumentCountIs(2),
> // The first argument must have the form x.c_str() or p->c_str() // where
> the method is string::c_str(). We can use the copy // constructor of
> string instead (or the compiler might share // the string object). HasArgument(
> 0, Id("call", Call( Callee(Id("member", MemberExpression())), Callee(Method(HasName(StringCStrMethod))),
> On(Id("arg", Expression()))))), // The second argument is the alloc object
> which must not be // present explicitly. HasArgument( 1,
> DefaultArgument()))
>
> The next steps will be to build up better support for in-process
> refactorings based on the Rewriter, to build up higher-level matchers for
> common patterns, and to extend the low-level matcher library.
>
> (rietveld link: http://codereview.appspot.com/4552059/)
>
> Cheers,
> /Manuel
>
>
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