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loop representation in gcc during parsing


Hi,

I'm trying to use GCC 4.3.0 for a program analysis frontend, and I've noticed that for, while, and do-while loops are all converted to a lower level representation using goto statements during the parsing phase. I've been trying to recover the source-code-like higher-level loop representation; however, I'm confused about a few things.

Consider the following nested for loop:

int i, j;
for(i = 0; i<size; i++)
{
   for(j=i, j>i, j--){
   ....
   }
   ...
}

In the function c_parser_for_statement in the file c-parser.c, it seems like the body of the outer for loop is an _empty statement list_. It seems to me that this statement list is somehow being correctly patched at a later point in time, but I don't quite understand how this works. My idea was to maintain a mapping from the original loop representation with the original loop body, init-expression, etc to the modified lower level gcc representation, but since the body is an empty statement list at this point, I can't recover the original structure of the loop.

I'd really appreciate any explanation about how specifically loops are converted to a lower-level representation and why the body of the loop looks like an empty statement list during parsing. Or if there is a better way of recovering the higher-level loop representation, I would also appreciate any tips about that.

Thanks a lot in advance,
Isil


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