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Re: Use gcc front-end for metrics

On 8/18/06, Roel Meeuws <> wrote:

In order to build a metrication tool I need a frontend that can
provide me with an abstract syntax tree containing information on all
actual language constructs in the code and also a CFG representation.
I reckon GCC has these capabilities and I was wondering if any of you
could tell me if it is possible to use just GCC's frontend.
Furthermore, where should I start, how do I extract the frontend from
GCC, which of the intermediate GCC representation could I use, are
they documented?

I would like to thank you in advance for any help you can give me.

Right, so you want to have a count of source level constructs, and basically something similar at the lower levels...

If you're going to do source level metrics, you will have to
instrument the front ends. All front ends, perhaps with the exception
of Ada and C++, have a pretty quick lowering to a level where you
won't be able to e.g. distinguish a for-loop from a while-loop, if
that would be something you're interested in. Depending on what
language you'll be analyzing, or rather how many of them, I'd suggest
you instrument the parser for your metrics, or forget about source
level constructs and just look at lower level information only.

As for CFG work, you should probably write a tree pass and insert it
at some point in the compilation schedule (see passes.c). Depending on
how close you want to stay to the original source code, you could put
the pass early or late. If you put it late, you can analyze the
optimized representation. In any case, you're going to find that gcc
will produce a CFG pretty early on for GIMPLE (gcc's three-address,
high level intermediate representation), but this happens _after_ the
front ends are done, and _after_ lowering to GIMPLE.

You can usually only find documentation on the front ends in the
source code, but the gcc online documentation can guide you a bit
there. So your first step would be to look at the GCC internals
documentation on You'll want to work
on GIMPLE (as opposed to RTL) which is reasonably well documented,
again in the GCC internals documentation.  And if you get stuck after
looking for a while, you'll usually find someone helpful on this list.

You may also want to look at the GCC wiki (
and the Introspector Project (

Hope this helps.


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