From: Basile Starynkevitch <bas...@starynkevitch.net>
Subject: Re: How to parse a code snippet at front-end plugin
Date: Sun, 12 Sep 2010 08:35:48 +0200
> On Sat, 11 Sep 2010 22:19:06 +0800 (CST)
> "Thinker K.F. Li" <thin...@codemud.net> wrote:
>
>> Hi,
>>
>> I am try to make a plugin to analyze GIMPLE before genericize. It
>> will insert some code defined by user into the tree. I want the user
>> to specify the inserted code in C. For example,
>>
>> --------------------------------------------------
>> {
>> static int i=0;
>>
>> printf("Hello %d\n", i++);
>> }
>> --------------------------------------------------
>>
>> I try to find a way to make C language parser of GCC to compile it for
>> me, and I will insert the code into the tree created from the main
>> source. But, it seems provide only functions to parse a complete C
>> source file, and I try to push a buffer to the reader of libcpp. But,
>> it does not work.
>
> I am not sure that there exist enough plugin hooks to do that (I am not sure
> even if there are plugin hooks to front-ends in GCC). However, I do see some
> way to perhaps implement what you suggest even in 4.5
>
> First, don't think of your problem as adding C code. Think of it as adding
> Gimple stuff into some Gimple representation.
> (I believe it is a case of aspect oriented programming, see
> http://en.wikipedia.org/wiki/Aspect-oriented_programming for more). But you
> want the user to specify the added code, using the already accepted C syntax
> of GCC (i.e. without hacking GCC parser).
>
> So you could use attributes & pragmas or builtins for that purpose.
>
> First, your user define its code snipped to insert as a C function with a
> special attribute, e.g.
>
> void say_hello(void) __attribute__((added_chunk));
>
> void say_hello(void)
> {
> static int i;
> printf("Hello %d\n", i++);
> }
>
> Then, your user would mark with another attribute every function into which
> your chunk should be added, perhaps
>
> int some_complex_function(int a, void*b)
> __attribute((insert_chunk(say_hello)));
>
> Or perhaps have a pragram asking this to insert the chunk in every function
> whose name start with some_
>
> #pragma GCCMELT insert_chunk_prefix(say_hello, some_)
>
This is a good idea that user can define rules in a included file and
include it in C files. I will try it. Thanks for your suggestion!
> The point here is that with the tricks above, you don't have to change GCC
> parser! and you could implement that using a plugin coded in C (this is not
> so simple, you have to filter Gimple). Better yet, you could implement that
> using GCC MELT http://gcc.gnu.org/wiki/MELT which provides pattern matching
> facilities on Gimple to make such tasks much simpler.
>
> You still have to understand Gimple & Tree in detail and find a good position
> in the pass machinery to insert your new pass or passes.
>
> If you succeed in making such a plugin please tell us. I would be delighted
> if you coded it in MELT, as a MELT extension.
>
> Good luck.
Actually, I have done something in C. It includes stuffs to filter
Gimple and insert chunks into original Gimple representation. I am
very glad to know MELT. I will try it. Thanks!
