refactor tail call transformer into a class - @RReverser
This commit is contained in:
Sebastian McKenzie
parent
87af83f1cb
commit
f1bca0013e
@ -1,163 +1,287 @@
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"use strict";
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var _ = require("lodash");
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var util = require("../../../util");
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var t = require("../../../types");
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var _ = require("lodash");
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function returnBlock(expr) {
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return t.blockStatement([t.returnStatement(expr)]);
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}
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function transformExpression(node, scope, state) {
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if (!node) return;
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function TailCall(node, scope, file) {
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this.hasTailRecursion = false;
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this.needsArguments = false;
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this.setsArguments = false;
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this.needsThis = false;
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this.ownerId = node.id;
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this.vars = [];
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return (function subTransform(node) {
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switch (node.type) {
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case "ConditionalExpression":
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var callConsequent = subTransform(node.consequent);
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var callAlternate = subTransform(node.alternate);
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if (!callConsequent && !callAlternate) {
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return;
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}
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// if ternary operator had tail recursion in value, convert to optimized if-statement
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node.type = "IfStatement";
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node.consequent = callConsequent ? t.toBlock(callConsequent) : returnBlock(node.consequent);
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if (callAlternate) {
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node.alternate = t.isIfStatement(callAlternate) ? callAlternate : t.toBlock(callAlternate);
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} else {
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node.alternate = returnBlock(node.alternate);
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}
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return [node];
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case "LogicalExpression":
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// only call in right-value of can be optimized
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var callRight = subTransform(node.right);
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if (!callRight) {
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return;
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}
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// cache left value as it might have side-effects
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var leftId = state.getLeftId();
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var testExpr = t.assignmentExpression(
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"=",
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leftId,
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node.left
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);
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if (node.operator === "&&") {
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testExpr = t.unaryExpression("!", testExpr);
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}
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return [t.ifStatement(testExpr, returnBlock(leftId))].concat(callRight);
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case "SequenceExpression":
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var seq = node.expressions;
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// only last element can be optimized
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var lastCall = subTransform(seq[seq.length - 1]);
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if (!lastCall) {
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return;
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}
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// remove converted expression from sequence
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// and convert to regular expression if needed
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if (--seq.length === 1) {
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node = seq[0];
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}
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return [t.expressionStatement(node)].concat(lastCall);
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case "CallExpression":
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var callee = node.callee, prop, thisBinding, args;
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if (t.isMemberExpression(callee, { computed: false }) &&
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t.isIdentifier(prop = callee.property)) {
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switch (prop.name) {
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case "call":
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args = t.arrayExpression(node.arguments.slice(1));
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break;
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case "apply":
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args = node.arguments[1] || t.identifier("undefined");
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break;
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default:
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return;
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}
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thisBinding = node.arguments[0];
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callee = callee.object;
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}
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// only tail recursion can be optimized as for now
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if (!t.isIdentifier(callee) || !scope.bindingEquals(callee.name, state.ownerId)) {
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return;
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}
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state.hasTailRecursion = true;
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var body = [];
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if (!t.isThisExpression(thisBinding)) {
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body.push(t.expressionStatement(t.assignmentExpression(
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"=",
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state.getThisId(),
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thisBinding || t.identifier("undefined")
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)));
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}
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if (!args) {
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args = t.arrayExpression(node.arguments);
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}
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var argumentsId = state.getArgumentsId();
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var params = state.getParams();
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body.push(t.expressionStatement(t.assignmentExpression(
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"=",
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argumentsId,
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args
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)));
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var i, param;
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if (t.isArrayExpression(args)) {
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var elems = args.elements;
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for (i = 0; i < elems.length && i < params.length; i++) {
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param = params[i];
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var elem = elems[i] || (elems[i] = t.identifier("undefined"));
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if (!param._isDefaultPlaceholder) {
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elems[i] = t.assignmentExpression("=", param, elem);
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}
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}
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} else {
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state.setsArguments = true;
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for (i = 0; i < params.length; i++) {
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param = params[i];
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if (!param._isDefaultPlaceholder) {
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body.push(t.expressionStatement(t.assignmentExpression(
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"=",
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param,
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t.memberExpression(argumentsId, t.literal(i), true)
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)));
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}
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}
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}
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body.push(t.continueStatement(state.getFunctionId()));
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return body;
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}
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})(node);
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this.scope = scope;
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this.file = file;
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this.node = node;
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}
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// Looks for and replaces tail recursion calls.
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TailCall.prototype.getArgumentsId = function () {
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return this.argumentsId = this.argumentsId || this.scope.generateUidIdentifier("arguments");
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};
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TailCall.prototype.getThisId = function () {
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return this.thisId = this.thisId || this.scope.generateUidIdentifier("this");
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};
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TailCall.prototype.getLeftId = function () {
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return this.leftId = this.leftId || this.scope.generateUidIdentifier("left");
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};
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TailCall.prototype.getFunctionId = function () {
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return this.functionId = this.functionId || this.scope.generateUidIdentifier("function");
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};
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TailCall.prototype.getParams = function () {
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var params = this.params;
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if (!params) {
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params = this.node.params;
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this.paramDecls = [];
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for (var i = 0; i < params.length; i++) {
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var param = params[i];
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if (!param._isDefaultPlaceholder) {
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this.paramDecls.push(t.variableDeclarator(
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param,
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params[i] = this.scope.generateUidIdentifier("x")
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));
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}
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}
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}
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return this.params = params;
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};
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TailCall.prototype.run = function () {
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var scope = this.scope;
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var node = this.node;
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// only tail recursion can be optimized as for now,
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// so we can skip anonymous functions entirely
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var ownerId = this.ownerId;
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if (!ownerId) return;
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// traverse the function and look for tail recursion
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scope.traverse(node, firstPass, this);
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if (!this.hasTailRecursion) return;
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//
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scope.traverse(node, secondPass, this);
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if (!this.needsThis || !this.needsArguments) {
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scope.traverse(node, thirdPass, this);
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}
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var body = t.ensureBlock(node).body;
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if (this.vars.length > 0) {
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body.unshift(t.expressionStatement(
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_(this.vars)
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.map(function (decl) {
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return decl.declarations;
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})
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.flatten()
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.reduceRight(function (expr, decl) {
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return t.assignmentExpression("=", decl.id, expr);
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}, t.identifier("undefined"))
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));
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}
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var paramDecls = this.paramDecls;
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if (paramDecls.length > 0) {
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body.unshift(t.variableDeclaration("var", paramDecls));
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}
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node.body = util.template("tail-call-body", {
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THIS_ID: this.thisId,
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ARGUMENTS_ID: this.argumentsId,
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FUNCTION_ID: this.getFunctionId(),
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BLOCK: node.body
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});
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var topVars = [];
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if (this.needsThis) {
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topVars.push(t.variableDeclarator(this.getThisId(), t.thisExpression()));
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}
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if (this.needsArguments || this.setsArguments) {
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var decl = t.variableDeclarator(this.getArgumentsId());
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if (this.needsArguments) {
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decl.init = t.identifier("arguments");
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}
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topVars.push(decl);
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}
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var leftId = this.leftId;
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if (leftId) {
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topVars.push(t.variableDeclarator(leftId));
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}
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if (topVars.length > 0) {
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node.body.body.unshift(t.variableDeclaration("var", topVars));
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}
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};
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TailCall.prototype.subTransform = function (node) {
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var handler = this["subTransform" + node.type];
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if (handler) return handler.call(this, node);
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};
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TailCall.prototype.subTransformConditionalExpression = function (node) {
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var callConsequent = this.subTransform(node.consequent);
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var callAlternate = this.subTransform(node.alternate);
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if (!callConsequent && !callAlternate) {
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return;
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}
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// if ternary operator had tail recursion in value, convert to optimized if-statement
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node.type = "IfStatement";
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node.consequent = callConsequent ? t.toBlock(callConsequent) : returnBlock(node.consequent);
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if (callAlternate) {
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node.alternate = t.isIfStatement(callAlternate) ? callAlternate : t.toBlock(callAlternate);
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} else {
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node.alternate = returnBlock(node.alternate);
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}
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return [node];
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};
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TailCall.prototype.subTransformLogicalExpression = function (node) {
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// only call in right-value of can be optimized
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var callRight = this.subTransform(node.right);
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if (!callRight) return;
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// cache left value as it might have side-effects
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var leftId = this.getLeftId();
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var testExpr = t.assignmentExpression(
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"=",
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leftId,
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node.left
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);
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if (node.operator === "&&") {
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testExpr = t.unaryExpression("!", testExpr);
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}
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return [t.ifStatement(testExpr, returnBlock(leftId))].concat(callRight);
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};
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TailCall.prototype.subTransformSequenceExpression = function (node) {
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var seq = node.expressions;
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// only last element can be optimized
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var lastCall = this.subTransform(seq[seq.length - 1]);
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if (!lastCall) {
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return;
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}
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// remove converted expression from sequence
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// and convert to regular expression if needed
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if (--seq.length === 1) {
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node = seq[0];
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}
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return [t.expressionStatement(node)].concat(lastCall);
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};
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TailCall.prototype.subTransformCallExpression = function (node) {
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var callee = node.callee, prop, thisBinding, args;
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if (t.isMemberExpression(callee, { computed: false }) &&
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t.isIdentifier(prop = callee.property)) {
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switch (prop.name) {
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case "call":
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args = t.arrayExpression(node.arguments.slice(1));
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break;
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case "apply":
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args = node.arguments[1] || t.identifier("undefined");
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break;
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default:
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return;
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}
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thisBinding = node.arguments[0];
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callee = callee.object;
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}
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// only tail recursion can be optimized as for now
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if (!t.isIdentifier(callee) || !this.scope.bindingEquals(callee.name, this.ownerId)) {
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return;
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}
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this.hasTailRecursion = true;
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var body = [];
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if (!t.isThisExpression(thisBinding)) {
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body.push(t.expressionStatement(t.assignmentExpression(
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"=",
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this.getThisId(),
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thisBinding || t.identifier("undefined")
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)));
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}
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if (!args) {
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args = t.arrayExpression(node.arguments);
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}
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var argumentsId = this.getArgumentsId();
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var params = this.getParams();
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body.push(t.expressionStatement(t.assignmentExpression(
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"=",
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argumentsId,
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args
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)));
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var i, param;
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if (t.isArrayExpression(args)) {
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var elems = args.elements;
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for (i = 0; i < elems.length && i < params.length; i++) {
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param = params[i];
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var elem = elems[i] || (elems[i] = t.identifier("undefined"));
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if (!param._isDefaultPlaceholder) {
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elems[i] = t.assignmentExpression("=", param, elem);
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}
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}
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} else {
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this.setsArguments = true;
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for (i = 0; i < params.length; i++) {
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param = params[i];
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if (!param._isDefaultPlaceholder) {
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body.push(t.expressionStatement(t.assignmentExpression(
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"=",
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param,
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t.memberExpression(argumentsId, t.literal(i), true)
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)));
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}
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}
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}
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body.push(t.continueStatement(this.getFunctionId()));
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return body;
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};
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// looks for and replaces tail recursion calls
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var firstPass = {
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enter: function (node, parent, scope, state) {
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if (t.isReturnStatement(node)) {
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this.skip();
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return transformExpression(node.argument, scope, state);
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return state.subTransform(node.argument);
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} else if (t.isTryStatement(parent)) {
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if (node === parent.block) {
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this.skip();
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@ -173,8 +297,8 @@ var firstPass = {
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}
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};
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// Hoists up function declarations, replaces `this` and `arguments` and
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// marks them as needed.
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// hoists up function declarations, replaces `this` and `arguments` and marks
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// them as needed
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var secondPass = {
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enter: function (node, parent, scope, state) {
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if (t.isThisExpression(node)) {
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@ -196,8 +320,7 @@ var secondPass = {
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}
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};
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// Optimizes recursion by removing `this` and `arguments`
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// if they are not used.
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// optimizes recursion by removing `this` and `arguments` if they aren't used
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var thirdPass = {
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enter: function (node, parent, scope, state) {
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if (!t.isExpressionStatement(node)) return;
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@ -213,112 +336,7 @@ var thirdPass = {
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}
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};
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exports.Function = function (node, parent, scope) {
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// only tail recursion can be optimized as for now,
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// so we can skip anonymous functions entirely
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var ownerId = node.id;
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if (!ownerId) return;
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var argumentsId, thisId, leftId, functionId, params, paramDecls;
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var state = {
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hasTailRecursion: false,
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needsThis: false,
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needsArguments: false,
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setsArguments: false,
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ownerId: ownerId,
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vars: [],
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getArgumentsId: function () {
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return argumentsId = argumentsId || scope.generateUidIdentifier("arguments");
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},
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getThisId: function () {
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return thisId = thisId || scope.generateUidIdentifier("this");
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},
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getLeftId: function () {
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return leftId = leftId || scope.generateUidIdentifier("left");
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},
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getFunctionId: function () {
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return functionId = functionId || scope.generateUidIdentifier("function");
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},
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getParams: function () {
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if (!params) {
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params = node.params;
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paramDecls = [];
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for (var i = 0; i < params.length; i++) {
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var param = params[i];
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if (!param._isDefaultPlaceholder) {
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paramDecls.push(t.variableDeclarator(
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param,
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params[i] = scope.generateUidIdentifier("x")
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));
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}
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}
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}
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return params;
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}
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};
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// traverse the function and look for tail recursion
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scope.traverse(node, firstPass, state);
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if (!state.hasTailRecursion) return;
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scope.traverse(node, secondPass, state);
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if (!state.needsThis || !state.needsArguments) {
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scope.traverse(node, thirdPass, state);
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}
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var body = t.ensureBlock(node).body;
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if (state.vars.length > 0) {
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body.unshift(t.expressionStatement(
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_(state.vars)
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.map(function (decl) {
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return decl.declarations;
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})
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.flatten()
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.reduceRight(function (expr, decl) {
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return t.assignmentExpression("=", decl.id, expr);
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}, t.identifier("undefined"))
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));
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}
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if (paramDecls.length > 0) {
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body.unshift(t.variableDeclaration("var", paramDecls));
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}
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||||
|
||||
node.body = util.template("tail-call-body", {
|
||||
THIS_ID: thisId,
|
||||
ARGUMENTS_ID: argumentsId,
|
||||
FUNCTION_ID: state.getFunctionId(),
|
||||
BLOCK: node.body
|
||||
});
|
||||
|
||||
var topVars = [];
|
||||
|
||||
if (state.needsThis) {
|
||||
topVars.push(t.variableDeclarator(state.getThisId(), t.thisExpression()));
|
||||
}
|
||||
|
||||
if (state.needsArguments || state.setsArguments) {
|
||||
var decl = t.variableDeclarator(state.getArgumentsId());
|
||||
if (state.needsArguments) {
|
||||
decl.init = t.identifier("arguments");
|
||||
}
|
||||
topVars.push(decl);
|
||||
}
|
||||
|
||||
if (leftId) {
|
||||
topVars.push(t.variableDeclarator(leftId));
|
||||
}
|
||||
|
||||
if (topVars.length > 0) {
|
||||
node.body.body.unshift(t.variableDeclaration("var", topVars));
|
||||
}
|
||||
exports.Function = function (node, parent, scope, file) {
|
||||
var tailCall = new TailCall(node, scope, file);
|
||||
tailCall.run();
|
||||
};
|
||||
|
||||
Loading…
x
Reference in New Issue
Block a user