Re: SSA code generators?

Srinivas Kankanahalli asks:


> Are there public domain programs that convert C code into Static
> Single Assignment form?? Any pointers will be greatly appreciated.


*Which* Static Single Assignment form are you looking for? SSA isn't
really a programming language; rather, it's a property of programs in a
language: A program in a language either is or is not in SSA.


Assuming that you're talking about a tool to convert C code into C code
which is in SSA form ...


Not that I am aware of. I also don't think that it's likely that such a
thing exists for the following reasons:


  o 2-address-code and SSA don't really mix very well, and C
      programs usually are chock-full of `2-address statements'. Consider
      the statement a += b, which would have to be converted into a = a + b
      before you could even attempt to convert it to SSA.


  o Contrary to what you write above, pointers are not greatly
      appreciated. :-) In fact, any statement that assigns to anything
      other than a (set of) scalar variables will bring about major
      headaches. See Section 3.1 of [cytron:91] for an idea of the inherent
      problems.


  o I can't think of any *use* for a C-program in SSA. This might,
      admittedly, be due to acute tunnel vision, but if it's not, it's
      unlikely that someone has gone through the effort of implementing
      such a tool.


That said, if you indeed find such a tool I'd like to hear about it. Also,
I'm curious what it is you're trying to achieve.


-----
Reference:


@article{cytron:91,
    title="Efficiently Computing Static Single Assignment Form and the
                                  Control Dependence Graph",
    author="Ron Cytron and Jeanne Ferrante and Barry K. Rosen and Mark
                                  N. Wegman and F. Kenneth Zadeck",
    pages="451--490",
    journal=toplas,
    year=1991,
    month=oct,
    volume=13,
    number=4
}


Alex
--
Alexander Vrchoticky alex@vmars.tuwien.ac.at
TU Vienna, CS/Real-Time Systems +43/1/58801-8168
--

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