Re: Looking for the GNU gcc grammar

tmk@netvision.net.il (Michael Tiomkin)
27 Apr 2003 02:09:05 -0400

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From: tmk@netvision.net.il (Michael Tiomkin)
Newsgroups: comp.compilers
Date: 27 Apr 2003 02:09:05 -0400
Organization: http://groups.google.com/
References: 03-04-044 03-04-051
Keywords: parse, tools
Posted-Date: 27 Apr 2003 02:09:05 EDT

foolishewe@hotmail.com (Bill Last Name Omitted) wrote in message news:03-04-051...
...
> After some preliminary source diving, I've found the expected Bison
> file which recognizes the nonterminals. However, I was surprised that
> I did not find a flex based scanner (it looks like they use ad hoc
> lexical analysis). Anyone know why they don't use flex for scanning?


    The reason of not using lex is compiler performance.
Usually, a compiler spends most of compile time in lexical analyzer,
and the easiest way to improve performance is to change the tokenizer.
    You are lucky that the C (and even gcc) keywords are simple and
well-known, and it is a relatively easy job to recover them.
    BTW, you can remove the typedef hack from the lexer and place it
in the parser (where it should belong if you want a decent grammar).


    Michael

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