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slice.js
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slice.js
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var walk = require('estraverse');
var worklist = require('analyses');
var common = require("../base/common.js");
var codegen = require('escodegen');
var SetTools = require("./settools.js");
var ASTTools = require("./../base/asttools.js");
var Set = worklist.Set;
module.exports = slice;
var Syntax = common.Syntax;
function slice(cfg, startNode, variable) {
if (!findVariableReferences(startNode.astNode).has(variable)) {
throw new Error("Illegal criterion for slicing: Variable '" + variable + "' not contained in " + codegen.generate(startNode.astNode));
}
var dominatorMap = computeInverseDominators(cfg);
var initialSet = new Set();
initialSet.add(variable);
var oldS = new Set(),
R = directRelevantVariables(cfg, startNode, initialSet, dominatorMap),
S = getRelevantStatements(cfg),
B = getRelevantBranchStatements(cfg, S);
while(!Set.equals(S, oldS)) {
oldS = S;
var newR = B.values().reduce(function(input, node) {
var sR = directRelevantVariables(cfg, node, findVariableReferences(node.astNode));
return mergeMap(input, sR );
}, R);
S = Set.union(B, getRelevantStatements(cfg));
B = getRelevantBranchStatements(cfg, S);
R = newR;
//Tools.printMap(cfg, newR);
}
//console.log("Statements final:", Tools.getSetLabels(S));
return S;
}
/**
*
* @param {} cfg
* @param {FlowNode} startNode
* @param {Set} variables
* @param {Map} dominatorMap
* @returns {Map.<FlowNode, Set>}
*/
function directRelevantVariables(cfg, startNode, variables, dominatorMap) {
var oldStart = cfg[1];
var oldNext = startNode.next;
cfg[1] = startNode;
cfg[1].next = [];
// console.log("Find direct: ", startNode.label, variables);
var R = worklist(cfg, function (input) {
if (this.type || !this.astNode)
return input;
// Local
var ref = this.ref = this.ref || findVariableReferences(this.astNode);
var def = this.def = this.def || SetTools.findVariableAssignments(this.astNode);
this.infl = this.infl || computeInfluence(this, dominatorMap.get(this));
var result = null;
if (Set.intersect(def, input).size) {
this.directRelevant = true;
result = Set.union(result, ref);
};
var generated = new Set(input.values().filter(function (v) {
return !def.has(v);
}));
return Set.union(result, generated);
}, {direction: 'backward', start: variables});
cfg[1].next = oldNext;
cfg[1] = oldStart;
return R;
}
function getRelevantStatements(cfg) {
return new Set(cfg[2].filter(function (node) {
return node.directRelevant === true;
}));
}
function getRelevantBranchStatements(cfg, S) {
return new Set(cfg[2].filter(function (node) {
return node.infl ? Set.intersect(node.infl, S).size : false;
}));
}
/**
*
* @param {Map.<FlowNode, Set>} A
* @param {Map.<FlowNode, Set>} B
*/
function mergeMap(A, B) {
var keys = B.keys();
for(var i in keys) {
var key = keys[i];
if(A.has(key)) {
var setA = A.get(key);
var setB = B.get(key);
A.set(key, Set.union(setA, setB));
}
}
return A;
}
function isMemberReference(node, parent) {
return node.type == Syntax.MemberExpression && node.object.type == Syntax.Identifier && node.property.type == Syntax.Identifier && !(parent.type === Syntax.CallExpression && parent.callee == node);
}
function getMemberName(node) {
if(node.object.type == Syntax.Identifier && node.property.type == Syntax.Identifier) {
return node.object.name + "." + node.property.name;
}
throw new Error("Could not determine member name: " + codegen.generate(node) + node.object.type);
}
function findVariableReferences(ast) {
var references = new Set();
var controller = new walk.Controller();
walk.traverse(ast, {
leave: function(node, parent) {
switch(node.type) {
case Syntax.AssignmentExpression:
references = Set.union(references, findVariableReferences(node.right));
controller.break();
break;
case Syntax.Identifier:
if (ASTTools.isVariableReference(node, parent)) {
references.add(node.name);
}
break;
case Syntax.MemberExpression:
if (isMemberReference(node, parent)) {
if (ASTTools.isVariableReference(node.object, node)) {
references.add(node.name);
}
references.add(getMemberName(node));
}
break;
case Syntax.CallExpression:
if(node.callee.type == Syntax.MemberExpression && parent && parent.type !== Syntax.MemberExpression) {
var object = node.callee.object;
if (object.type == Syntax.Identifier) {
references.add(object.name)
}
}
break;
}
}
})
return references;
}
var Tools = {
findSetOfNodesOnPath: function(fromArr, endSet, result) {
//console.log("Testing: ", from.label || from.type);
for(var i = 0; i < fromArr.length; i++) {
var node = fromArr[i];
if(!(result.has(node) || endSet.has(node))) {
result.add(node);
Tools.findSetOfNodesOnPath(node.next, endSet, result);
}
}
}
}
function computeInfluence(node, inverseDominators) {
var result = new Set();
// INFL(node) will be empty unless b has more than one immediate
// successor (i.e., is a branch statement).
if (node.next.length < 2)
return result;
Tools.findSetOfNodesOnPath(node.next, inverseDominators, result);
//console.log("INFL(", node.label, "):", Tools.getSetLabels(result))
return result;
}
function computeInverseDominators(cfg) {
var result = worklist(cfg, function (input) {
if (this.type || !this.astNode)
return input;
return Set.union(input, new Set([this]));
}, {direction: 'backward', start: new Set(), merge: worklist.merge(Set.intersect)});
//Tools.printMap(cfg, result);
return result;
}