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Liberal use of `Compressor.transform()` and `AST_Node.optimize()` presents an issue for look-up operations like `TreeWalker.in_boolean_context()` and `TreeWalker.parent()`. This is an incremental fix such that `AST_Node.optimize()` would now contain the correct stack information when called correctly.
alexlamsl
commented
Mar 14, 2017
| opt._optimized = true; | ||
| if (opt === self) return opt; | ||
| return opt.transform(compressor); | ||
| return opt; |
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Problem with calling opt.transform(compressor) here is that the stack would change from:
...
...
self
to:
...
...
self
opt
which will cause optimisations that depend knowing where they are in the AST to fail.
The solution is to wait for opt to be assigned on the relevant field in the parent AST_Node, then descend() from the parent again. As this node is already marked as _optimized, only its children be altered by optimize().
alfaproject
reviewed
Mar 14, 2017
| if (was_scope && node instanceof AST_Scope) { | ||
| node.drop_unused(this); | ||
| descend(node, this); | ||
| descend(node, this); |
alexlamsl
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Mar 15, 2017
alexlamsl
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Mar 15, 2017
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Liberal use of
Compressor.transform()andAST_Node.optimize()presents an issue for look-up operations likeTreeWalker.in_boolean_context()andTreeWalker.parent().This is an incremental fix such that
AST_Node.optimize()would now contain the correct stack information when called correctly.This is less ambitious than #1593, and attempting to gradually patch up incorrect usages without incurring performance penalties.