# Lecture7 - SSA Construction Lecture 7 CS 501 April 22, 2009...

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SSA Construction Lecture 7 CS 501 April 22, 2009 1

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Preliminaries Critiques EfFciently Computing Static Single Assignment ±orm and the Control Dependence Graph Cytron, Ferrante, Rosen, Wegman, and Zadeck HW 2 now posted Building, using SSA 2
Overview Quick review of SSA Building SSA Dominance frontiers Inserting Φ instructions Renaming variables to unique versions Loop invariant code motion Translating out of SSA 3

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Recap Static single assignment form (SSA) Sparse data Fow representation between de±nitions and uses: Each de±nition is a unique assignment Each use refers to a single de±nition Φ introduced at merge points Enhances / simpli±es many optimizations 4
Straight-line example 5

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Merge points V = 1 V = 2 V = 3 Y = V Z = V X = V 6
Merge points V 1 = 1 V 2 = 2 V 3 = 3 V 4 = ! (V 1, V 2, V 3) Y = V 4 Z = V 4 X = V 4 7

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v = 0 v = 1 x = v v = foo() y = v v = x + 1 A B C D E F G H I Another example 8
Another example v1 = 0 v3 = 1 v5 = ! (v1,v2) x = v5 v4 = foo() v6 = ! (v3,v4) v7 = ! (v2,v6) y = v7 v2 = x + 1 A B C D E F G H I 9

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Constraints on SSA 10
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## This note was uploaded on 02/09/2012 for the course CSE 403 taught by Professor Staff during the Spring '08 term at University of Washington.

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Lecture7 - SSA Construction Lecture 7 CS 501 April 22, 2009...

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