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157 lines
4.7 KiB
JavaScript
157 lines
4.7 KiB
JavaScript
/*
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* Optimalization passes made on the grammar AST before compilation. Each pass
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* is a function that is passed the AST and returns a new AST. The AST can be
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* modified in-place by the pass. The order in which the passes are run is
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* specified in |PEG.compiler.compile| and should be the same as the order of
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* definitions here.
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*/
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PEG.compiler.passes = {
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/*
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* Removes proxy rules -- that is, rules that only delegate to other rule.
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*/
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proxyRules: function(ast) {
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function isProxyRule(node) {
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return node.type === "rule" && node.expression.type === "rule_ref";
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}
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function replaceRuleRefs(ast, from, to) {
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function nop() {}
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function replaceInExpression(node, from, to) {
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replace(node.expression, from, to);
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}
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function replaceInSubnodes(propertyName) {
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return function(node, from, to) {
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each(node[propertyName], function(subnode) {
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replace(subnode, from, to);
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});
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};
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}
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var replace = buildNodeVisitor({
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grammar:
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function(node, from, to) {
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for (var name in node.rules) {
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replace(node.rules[name], from, to);
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}
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},
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rule: replaceInExpression,
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choice: replaceInSubnodes("alternatives"),
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sequence: replaceInSubnodes("elements"),
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labeled: replaceInExpression,
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simple_and: replaceInExpression,
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simple_not: replaceInExpression,
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semantic_and: nop,
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semantic_not: nop,
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optional: replaceInExpression,
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zero_or_more: replaceInExpression,
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one_or_more: replaceInExpression,
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action: replaceInExpression,
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rule_ref:
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function(node, from, to) {
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if (node.name === from) {
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node.name = to;
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}
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},
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literal: nop,
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any: nop,
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"class": nop
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});
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replace(ast, from, to);
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}
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for (var name in ast.rules) {
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if (isProxyRule(ast.rules[name])) {
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replaceRuleRefs(ast, ast.rules[name].name, ast.rules[name].expression.name);
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if (name === ast.startRule) {
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ast.startRule = ast.rules[name].expression.name;
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}
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delete ast.rules[name];
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}
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}
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return ast;
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},
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/*
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* Adds |resultStackDepth| and |posStackDepth| properties to each AST node.
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* These properties specify how many positions on the result or position stack
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* code generated by the emitter for the node will use. This information is
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* used to declare varibles holding the stack data in the generated code.
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*/
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stackDepths: function(ast) {
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function computeZeroes(node) {
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node.resultStackDepth = 0;
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node.posStackDepth = 0;
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}
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function computeFromExpression(resultStackDelta, posStackDelta) {
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return function(node) {
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compute(node.expression);
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node.resultStackDepth = node.expression.resultStackDepth + resultStackDelta;
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node.posStackDepth = node.expression.posStackDepth + posStackDelta;
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};
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}
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var compute = buildNodeVisitor({
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grammar:
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function(node) {
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for (var name in node.rules) {
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compute(node.rules[name]);
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}
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},
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rule: computeFromExpression(1, 1),
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choice:
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function(node) {
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each(node.alternatives, compute);
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node.resultStackDepth = Math.max.apply(
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null,
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map(node.alternatives, function(e) { return e.resultStackDepth; })
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);
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node.posStackDepth = Math.max.apply(
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null,
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map(node.alternatives, function(e) { return e.posStackDepth; })
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);
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},
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sequence:
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function(node) {
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each(node.elements, compute);
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node.resultStackDepth = 1 + Math.max.apply(
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null,
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map(node.elements, function(e, i) { return i + e.resultStackDepth; })
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);
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node.posStackDepth = 1 + Math.max.apply(
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null,
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map(node.elements, function(e) { return e.posStackDepth; })
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);
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},
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labeled: computeFromExpression(0, 0),
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simple_and: computeFromExpression(0, 1),
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simple_not: computeFromExpression(0, 1),
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semantic_and: computeZeroes,
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semantic_not: computeZeroes,
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optional: computeFromExpression(0, 0),
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zero_or_more: computeFromExpression(1, 0),
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one_or_more: computeFromExpression(1, 0),
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action: computeFromExpression(0, 1),
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rule_ref: computeZeroes,
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literal: computeZeroes,
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any: computeZeroes,
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"class": computeZeroes
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});
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compute(ast);
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return ast;
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}
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};
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