test

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• // expensive | expensive can be turned into expensive ? 1 : expensive, and
• // expensive | cheap can be turned into cheap ? 1 : expensive,
• // so that we can avoid the expensive computation, if it has no side effects.
• function conditionalize(ast) {
• var MIN_COST = 4;
• traverse(ast, function(node, type) {
• if (type === 'if' || type === 'while') {
• var cond = node[1];
• if (cond[0] === 'binary' && (cond[1] === '|' || cond[1] === '&') && cond[3][0] !== 'num' && cond[2][0] !== 'num') {
• // logical operator on two non-numerical values, all inside a condition
• var left = cond[2];
• var right = cond[3];
• var leftEffects = hasSideEffects(left);
• var rightEffects = hasSideEffects(right);
• if (leftEffects && rightEffects) return; // both must execute
• // canonicalize with side effects, if any, happening on the left
• if (rightEffects) {
• if (measureSize(left) < MIN_COST) return; // avoidable code is too cheap
• var temp = left;
• left = right;
• right = temp;
• } else if (leftEffects) {
• if (measureSize(right) < MIN_COST) return; // avoidable code is too cheap
• } else {
• // no side effects, reorder based on cost estimation
• var leftCost = measureSize(left);
• var rightCost = measureSize(right);
• if (Math.max(leftCost, rightCost) < MIN_COST) return; // avoidable code is too cheap
• // canonicalize with expensive code on the right
• if (leftCost > rightCost) {
• var temp = left;
• left = right;
• right = temp;
• }
• }
• // worth it, perform conditionalization
• if (cond[1] === '|') {
• node[1] = ['conditional', left, ['num', 1], right];
• } else { // &
• node[1] = ['conditional', left, right, ['num', 0]];
• }

[kripken]

• // expensive | expensive can be turned into expensive ? 1 : expensive, and
• // expensive | cheap can be turned into cheap ? 1 : expensive,
• // so that we can avoid the expensive computation, if it has no side effects.
• function conditionalize(ast) {
• var MIN_COST = 4;
• traverse(ast, function(node, type) {
• if (type === 'if' || type === 'while') {
• var cond = node[1];
• if (cond[0] === 'binary' && (cond[1] === '|' || cond[1] === '&') && cond[3][0] !== 'num' && cond[2][0] !== 'num') {
• // logical operator on two non-numerical values, all inside a condition
• var left = cond[2];
• var right = cond[3];
• var leftEffects = hasSideEffects(left);
• var rightEffects = hasSideEffects(right);
• if (leftEffects && rightEffects) return; // both must execute
• // canonicalize with side effects, if any, happening on the left
• if (rightEffects) {
• if (measureSize(left) < MIN_COST) return; // avoidable code is too cheap
• var temp = left;
• left = right;
• right = temp;
• } else if (leftEffects) {
• if (measureSize(right) < MIN_COST) return; // avoidable code is too cheap
• } else {
• // no side effects, reorder based on cost estimation
• var leftCost = measureSize(left);
• var rightCost = measureSize(right);
• if (Math.max(leftCost, rightCost) < MIN_COST) return; // avoidable code is too cheap
• // canonicalize with expensive code on the right
• if (leftCost > rightCost) {
• var temp = left;
• left = right;
• right = temp;
• }
• }
• // worth it, perform conditionalization
• if (cond[1] === '|') {
• node[1] = ['conditional', left, ['num', 1], right];
• } else { // &
• node[1] = ['conditional', left, right, ['num', 0]];
• }