Re: Are SSA and reaching definitions equivalent?

bromage@goaway.cc.monash.edu.au (Andrew Bromage)
7 Apr 2002 00:48:30 -0500

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Related articles
Are SSA and reaching definitions equivalent? dakupoto@tick.ece.utexas.edu (Amal Banerjee) (2002-04-06)
Re: Are SSA and reaching definitions equivalent? bromage@goaway.cc.monash.edu.au (2002-04-07)
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From: bromage@goaway.cc.monash.edu.au (Andrew Bromage)
Newsgroups: comp.compilers
Date: 7 Apr 2002 00:48:30 -0500
Organization: Monash Uni
References: 02-04-030
Keywords: analysis
Posted-Date: 07 Apr 2002 00:48:30 EST

G'day all.


Amal Banerjee <dakupoto@tick.ece.utexas.edu> writes:


> Are SSA and reaching definitions equivalent? If so what would be a
> formal way to prove/disprove it?


SSA form gives you more information than reaching definitions, namely,
the paths along which the definitions reach. That can be useful (e.g.
for constructing an interference graph, or for conditional constant
propagation), but otherwise I believe they're identical.


I haven't seen a formal proof, but I would think that proving that
reaching definition information can be obtained from SSA form should
be straightforward: you just trace the chains backwards through phi
nodes, after all.


Cheers,
Andrew Bromage

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