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Optimization: eliminate unnecessary checks for result of parse, when …
…it can be statically determined
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,173 @@ | ||
| "use strict"; | ||
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| const visitor = require( "../visitor" ); | ||
| const asts = require( "../asts" ); | ||
| const GrammarError = require( "../../grammar-error" ); | ||
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| // Inference match result of the rule. Can be: | ||
| // -1: negative result, always fails | ||
| // 0: neutral result, may be fail, may be match | ||
| // 1: positive result, always match | ||
| function inferenceMatchResult( ast ) { | ||
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| let inference; | ||
| function sometimesMatch( node ) { | ||
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| node.match = 0; | ||
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| return node.match; | ||
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| } | ||
| function alwaysMatch( node ) { | ||
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| inference( node.expression ); | ||
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| node.match = 1; | ||
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| return node.match; | ||
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| } | ||
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| function inferenceExpression( node ) { | ||
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| node.match = inference( node.expression ); | ||
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| return node.match; | ||
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| } | ||
| function inferenceElements( elements, forChoice ) { | ||
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| const length = elements.length; | ||
| let always = 0; | ||
| let never = 0; | ||
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| for ( let i = 0; i < length; ++i ) { | ||
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| const result = inference( elements[ i ] ); | ||
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| if ( result > 0 ) { | ||
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| ++always; | ||
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| } | ||
| if ( result < 0 ) { | ||
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| ++never; | ||
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| } | ||
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| } | ||
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| if ( always === length ) { | ||
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| return 1; | ||
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| } | ||
| if ( forChoice ) { | ||
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| return never === length ? -1 : 0; | ||
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| } | ||
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| return never > 0 ? -1 : 0; | ||
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| } | ||
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| inference = visitor.build( { | ||
| rule( node ) { | ||
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| let oldResult; | ||
| let count = 0; | ||
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| if ( typeof node.match === "undefined" ) { | ||
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| node.match = 0; | ||
| do { | ||
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| oldResult = node.match; | ||
| node.match = inference( node.expression ); | ||
| // 6 == 3! -- permutations count for all transitions from one match | ||
| // state to another. | ||
| // After 6 iterations the cycle with guarantee begins | ||
| // istanbul ignore next | ||
| if ( ++count > 6 ) { | ||
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| throw new GrammarError( | ||
| "Infinity cycle detected when trying evaluate node match result", | ||
| node.location | ||
| ); | ||
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| } | ||
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| } while ( oldResult !== node.match ); | ||
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| } | ||
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| return node.match; | ||
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| }, | ||
| named: inferenceExpression, | ||
| choice( node ) { | ||
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| node.match = inferenceElements( node.alternatives, true ); | ||
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| return node.match; | ||
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| }, | ||
| action: inferenceExpression, | ||
| sequence( node ) { | ||
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| node.match = inferenceElements( node.elements, false ); | ||
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| return node.match; | ||
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| }, | ||
| labeled: inferenceExpression, | ||
| text: inferenceExpression, | ||
| simple_and: inferenceExpression, | ||
| simple_not( node ) { | ||
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| node.match = -inference( node.expression ); | ||
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| return node.match; | ||
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| }, | ||
| optional: alwaysMatch, | ||
| zero_or_more: alwaysMatch, | ||
| one_or_more: inferenceExpression, | ||
| group: inferenceExpression, | ||
| semantic_and: sometimesMatch, | ||
| semantic_not: sometimesMatch, | ||
| rule_ref( node ) { | ||
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| const rule = asts.findRule( ast, node.name ); | ||
| node.match = inference( rule ); | ||
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| return node.match; | ||
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| }, | ||
| literal( node ) { | ||
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| // Empty literal always match on any input | ||
| node.match = node.value.length === 0 ? 1 : 0; | ||
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| return node.match; | ||
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| }, | ||
| class( node ) { | ||
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| // Empty character class never match on any input | ||
| node.match = node.parts.length === 0 ? -1 : 0; | ||
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| return node.match; | ||
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| }, | ||
| // |any| not match on empty input | ||
| any: sometimesMatch | ||
| } ); | ||
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| inference( ast ); | ||
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| } | ||
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| module.exports = inferenceMatchResult; |
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