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Re: [Gnu-arch-users] Slow inventories on large source trees

From: Tom Lord
Subject: Re: [Gnu-arch-users] Slow inventories on large source trees
Date: Thu, 22 Apr 2004 08:52:56 -0700 (PDT)

    > From: Aaron Bentley <address@hidden>

    > Tom Lord wrote:

    > > Abently, are you interested in working on this?  Do you know about the
    > > `cut' operator in Rx?  (I.e., you don't want to combine those
    > > filename_matches calls by adding parentheses to regexps.  You want to
    > > arrange for the final state label of the dfa to tell you which pattern
    > > matched.)

    > Okay, I've tried it, and it's a horrible pessimization.  I don't 
    > understand why.  

Don't panic.   I need to tweak Rx.

I assume that you are passing a regmatch_t array with just one
element, right?

The cut operator can work with just a simple DFA translation of a
regexp -- and Rx supports that internally -- but it appears that 
the test for whether or not that optimization applies within the posix
entry points doesn't know about `cut'.   It's as if you had asked for
a full set of `regmatch_t' values --- Rx is doing lots of backtracking
work on every match.

I'll fix it early next week.


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