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From last class
The above is Click’s solution (PLDI 95)
The above is Click’s solution (PLDI 95)
Control Dependences
• A node (basic block) Y is controldependent on
another X iff X determines whether Y executes
– there exists a path from X to Y s.t. every node in the
path other than X and Y is postdominated by Y
– X is not postdominated by Y
Control Dependences
• A node (basic block) Y is controldependent on
another X iff X determines whether Y executes
– there exists a path from X to Y s.t. every node in the
path other than X and Y is postdominated by Y
– X is not postdominated by Y
Example
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Example
Control Dependence Graph
• Control dependence graph: Y decsendent of X iff
Y is control dependent on Y
– label each child edge with required condition
– group all children with same condition under region
node
• Program dependence graph: superimpose
dataflow graph (in SSA form or not) on top of the
control dependence graph
Example
Example
Another example
Another example
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 Fall '06
 Lerner

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