[PATCH] speedup matching of ^$ and cleanup some code in regex

[Paolo Bonzini <bonzini at gnu dot org>]

Regex matching has an optimization where only one match is tried for a 
regex anchored to the beginning of the buffer. While other anchors are 
resolved with the fastmap, this one allows further optimization and is 
special cased. However, because of a bug in create_cd_newstate, ^$ would 
be mistakenly treated as a non-anchoring match, and re_search_internal 
would try matching it at every position.

In fact, the bug is (almost) fixed by this hunk:

@@ -1682,8 +1680,6 @@ create_cd_newstate (const re_dfa_t *dfa,
        newstate->halt = 1;
       else if (type == OP_BACK_REF)
        newstate->has_backref = 1;
-      else if (type == ANCHOR)
-       constraint = node->opr.ctx_type;

       if (constraint)
        {


However, some complications in building the NFA prevent this from fixing 
the problem. Therefore, this patch cleans up the handling of anchors so 
that tests on type == ANCHOR are not necessary anymore. When creating 
the NFA (calc_first), I move the opr.ctx_type to the constraint field of 
re_token_t, and then I always look at it unconditionally, without 
special-casing ANCHORs. This also allows some simplification of 
duplicate_node_closure.

Patch at http://sourceware.org/bugzilla/attachment.cgi?id=2690&action=view

Paolo