### Description

Compute static single assignment form of a graph.

### Author

Richard Kelsey; ported to Chicken by Ivan Raikov

### Version

• 1.0 Initial release

graph-ssa.egg

### 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

procedure: graph->ssa-graph:: G -> SSA-GRAPH

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

procedure: graph-ssa-find-joins:: SSA-GRAPH -> NODES

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)

```

```Copyright (c) 1993-1999 by Richard Kelsey.

Ported to Chicken Scheme by Ivan Raikov.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:

1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.

3. The names of its contributors may not be used to endorse or promote
products derived from this software without specific prior written
permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER
OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.```