## graph-ssa

Compute static single assignment form of a graph.

## Usage

(require-extension graph-ssa)

## Documentation

This code is based on the algorithm from Efficiently computing static single assignment form and the control dependence graph, ACM Transactions on Programming Languages and Systems 1991 13(4), pp. 451-490.

### Procedures

graph->ssa-graph:procedure

Computes the dominance frontiers of the nodes in the graph, and returns the list of nodes augmented with this information.

graph-ssa-find-joins:procedure

Given a list of SSA nodes, returns the list of nodes N for which there are (at least) two paths ... N_0 M_0 ... M_i N and ... N_1 P_0 ... P_j N such that N_0 and N_1 are distinct members of NODES and the M's and P's are disjoint sets.

## Examples

```(require-extension srfi-1)
(require-extension digraph)
(require-extension graph-dominators)

(define used-by '((a . b) (b . c) (c . d) (c . b) (b . e) (d . d) (d . e) ))

(define g (make-digraph 'cfg "control flow graph"))

(define node-list (delete-duplicates
(concatenate (list (map car used-by) (map cdr used-by)))))

(define node-ids (list-tabulate (length node-list) values))

(for-each (lambda (i n) ((g 'add-node!) i (list #f n))) node-ids node-list)
(define node-map (zip node-list node-ids))

(for-each (lambda (e)
(match e ((ni . nj) (let ((i (car (alist-ref ni node-map)))
(j (car (alist-ref nj node-map))))
((g 'add-edge!) (list i j (format "~A->~A" ni nj)))))
(else (error "invalid edge " e))))
used-by)

(define ssa-graph (graph->ssa-graph g))
(graph-ssa-find-joins ssa-graph)

```

### Author

Richard Kelsey; ported to Chicken by Ivan Raikov

### Version history

1.3
Documentation converted to wiki format
1.2
Ported to Chicken 4
1.0
Initial release

```Copyright by Richard Kelsey.

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