|Text of Jim Welsh and Atholl Hay: A Model Implementation of Standard P firstname.lastname@example.org (Hans Otten) (2004-07-13)|
|Re: Text of Jim Welsh and Atholl Hay: A Model Implementation of Standa email@example.com (Franck Pissotte) (2004-07-15)|
|Number of Phi-functions in SSA graph firstname.lastname@example.org (Bageshri Sathe) (2005-03-24)|
|Re: Number of Phi-functions in SSA graph email@example.com (Diego Novillo) (2005-03-25)|
|Re: Number of Phi-functions in SSA graph firstname.lastname@example.org (Nathan Moore) (2005-03-25)|
|Re: Number of Phi-functions in SSA graph email@example.com (F. Liekweg) (2005-03-25)|
|Re: Number of Phi-functions in SSA graph Martin.Ward@durham.ac.uk (Martin Ward) (2005-03-31)|
|Re: Number of Phi-functions in SSA graph firstname.lastname@example.org (Jeremy Singer) (2005-04-11)|
|Interprocedural Constant Propagation email@example.com (Bageshri Sathe) (2005-04-30)|
|From:||Diego Novillo <firstname.lastname@example.org>|
|Date:||25 Mar 2005 21:54:19 -0500|
|Organization:||Red Hat Canada|
|References:||04-07-030 04-07-041 05-03-086|
On Thu, Mar 24, 2005 at 09:15:05PM -0500, Bageshri Sathe wrote:
> I was wondering what is the upper bound on number of phi-functions in a
> minimal SSA graph. Does it depend upon number of program variables or join
> nodes in the CFG or both?
I assume that you mean minimal in the original sense (i.e., PHI nodes
are always added to the iterated dominance frontier of definition
sites). The pruned and semi-pruned forms will actually yield a
smaller number of PHI nodes, as the IDFs are pruned with live-in
The main factor is the size of the iterated dominance frontier of each
definition site, and, of course, the number of definition sites.
For instance, if you have a very convoluted graph but all the
definitions are in the entry block, there will be exactly 0 PHI nodes
(the example is extreme and is only meant as an illustration). At the
other extreme, you may have just 1 definition site that is very "deep"
inside the CFG and has a huge IDF. Each block in that IDF will need a
> Any literature that discusses this?
The various papers that describe techniques for PHI placement should
help, but I'm not aware of anything that discusses this particular
topic in detail.
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