Re: Newbie SSA question

Martin.Ward@durham.ac.uk (Martin Ward)
1 Feb 2001 17:39:34 -0500

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Re: Newbie SSA question Martin.Ward@durham.ac.uk (2001-02-01)
Re: Newbie SSA question pmk@visi.com (2001-02-12)
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From: Martin.Ward@durham.ac.uk (Martin Ward)
Newsgroups: comp.compilers
Date: 1 Feb 2001 17:39:34 -0500
Organization: Compilers Central
References: 01-01-147
Keywords: analysis
Posted-Date: 01 Feb 2001 17:39:34 EST

Kevin Tucker (Kevin.Tucker@Microchip.com) writes:
> The question is, when converting to SSA form, are you actually
> allocating new variables for each assignment, or are you just "renaming"
> them for notational purposes?.


If you simply convert to SSA and then back again, then it doesn't matter
which you do. But you usually convert to SSA form in order to do some
further optimisations, in which case you can't necessarily just
"drop the subscripts" to convert back. Translate the phi functions
to a set of assignments (one on each incoming egde) and then do
register allocation to eliminate the extra moves. See Section 19.6
of "Modern Compiler Implementation in C" by Andrew W. Appel.


Martin


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