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feat(codegen): unfold constant expressions and eliminate dead branches
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,92 @@ | ||
| import internalScope from '../templates/internal-scope.mjs'; | ||
| import scope from '../templates/scope.mjs'; | ||
|
|
||
| function dropNode(branch, i) { | ||
| branch.splice(i, 1); | ||
| return i - 1; | ||
| } | ||
|
|
||
| function leftOrRight(node, left, right) { | ||
| if (left === null) { | ||
| return right; | ||
| } else if (right === null) { | ||
| return left; | ||
| } | ||
|
|
||
| node.left = left; | ||
| node.right = right; | ||
|
|
||
| return node; | ||
| } | ||
|
|
||
| function reduceBinaryExpression(node) { | ||
| if (node.operator === '<' && node.left === scope.depth) { | ||
| return null; | ||
| } | ||
|
|
||
| return leftOrRight(node, eliminate(node.left), eliminate(node.right)); | ||
| } | ||
|
|
||
| function eliminate(node) { | ||
| switch (node.type) { | ||
| case 'AssignmentExpression': | ||
| if (node.left !== internalScope.pos) { | ||
| return node; | ||
| } | ||
|
|
||
| return eliminate(node.right); | ||
| case 'ConditionalExpression': | ||
| if ( | ||
| node.consequent.type === 'NumericLiteral' && | ||
| node.consequent.value === -1 | ||
| ) { | ||
| return eliminate(node.test); | ||
| } | ||
|
|
||
| return node; | ||
| case 'SequenceExpression': | ||
| return eliminate(node.expressions[0]); | ||
| case 'LogicalExpression': | ||
| return leftOrRight(node, eliminate(node.left), eliminate(node.right)); | ||
| case 'BinaryExpression': | ||
| return reduceBinaryExpression(node); | ||
| case 'IfStatement': | ||
| return eliminate(node.test); | ||
| case 'Identifier': | ||
| if (node === internalScope.pos) { | ||
| return null; | ||
| } | ||
|
|
||
| return node; | ||
| case 'MemberExpression': | ||
| node.property = eliminate(node.property); | ||
| return node; | ||
| default: | ||
| return node; | ||
| } | ||
| } | ||
|
|
||
| export default function optimizer(branch, iterator) { | ||
| if (iterator.feedback.mutatesPos) return; | ||
|
|
||
| let i = Math.max(0, Math.min(1, iterator.length)); | ||
|
|
||
| for (; i < branch.length; i++) { | ||
| const node = branch[i]; | ||
| if ( | ||
| node.type === 'VariableDeclaration' && | ||
| node.kind === 'let' && | ||
| node.declarations[0].id === internalScope.pos | ||
| ) { | ||
| i = dropNode(branch, i); | ||
| continue; | ||
| } | ||
|
|
||
| const test = eliminate(node); | ||
| if (test === null || test === scope.depth) { | ||
| i = dropNode(branch, i); | ||
| } else { | ||
| node.test = test; | ||
| } | ||
| } | ||
| } |