Tue, 15 Mar 2011 20:50:15 -0700 (PDT)

Related articles |
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aycock's algorithm for ssa n.oje.bar@gmail.com (nojb) (2011-03-15) |

Re: aycock's algorithm for ssa nikolaos.kavvadias@gmail.com (Nikolaos Kavvadias) (2011-03-17) |

From: | nojb <n.oje.bar@gmail.com> |

Newsgroups: | comp.compilers |

Date: | Tue, 15 Mar 2011 20:50:15 -0700 (PDT) |

Organization: | Compilers Central |

Keywords: | analysis, question |

Posted-Date: | 16 Mar 2011 11:15:25 EDT |

Hello,

I'm trying to understand Aycock's algorithm for computing SSA form

("Simple Generation of Static Single Assignment Form"). Googling

hasn't turned up anything useful.

He proceeds in two steps, first he adds every possible phi-function

(i.e. one for every function in the control flow graph, in every basic

block) and then he eliminates many of these by iterating two steps:

1. remove phi-functions of the form v_i = phi(v_i,...,v_i) (his

notation)

2. remove phi-functions of the form v_i = phi(v_i,...,v_i, v_j) and

replace allt he ocurrences

of v_i with v_j. (idem for all the permutations of the operands of

phi).

My first problem is with step 1. I don't understand what he means by

v_i = phi(v_i, ...,v_i). Does he mean that all the phi operands are

the same? Then that would be a strange notation indeed...

Same question for 2.

Thanks!

N

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