# Re: A question about Dominators

## vbdis@aol.com (VBDis)20 Dec 2001 00:33:56 -0500

From comp.compilers

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 From: vbdis@aol.com (VBDis) Newsgroups: comp.compilers Date: 20 Dec 2001 00:33:56 -0500 Organization: AOL Bertelsmann Online GmbH & Co. KG http://www.germany.aol.com References: 01-12-067 Keywords: analysis Posted-Date: 20 Dec 2001 00:33:56 EST

"Robert Sherry" <rsherry8@home.com>schreibt:
>The basic idea of the first approach is that node a
>dominates node b if and only if a=b or a is the unique immediate predecessor
>of b or b has more then one immediate predecessor and for all immediate
>predecessors c of b, c is not equal to a and a dominates c.

IMO it's a matter of taste/convention, whether a node dominates itself
(a=b). But I definitely see no reason, why the dominator cannot be
one of multiple immediate predecessors.

In a graph with the edges (a,b), (a,c), (b,c) node a dominates both
nodes b and c.

Node a dominates node b if a=b, or for all immediate predecessors c of b, a
dominates c.

Now the case a=b also makes sense, since when node a is an immediate
predecessor of b, then node a dominates itself (as predecessor c of b). It's
not required that a<>c, and a single predecessor is only a special case of
multiple predecessors.

BTW, do you have an equivalent definition or idea for post-dominators?

DoDi

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