chakra-core/ChakraCore

Optimize OP_LdCustomSpreadIteratorList for arguments object

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#1,230 opened on Jul 1, 2016

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PerformanceProposalSuggestiongood first issuehelp wanted

Description

I was looking into the code of OP_LdCustomSpreadIteratorList and noticed that we optimize it by not creating SpreadArgument if parameter passed to OP_LdCustomSpreadIteratorList does not have user defined iterator. We do this check only for JavascriptArray and TypedArrayBase and we can expand it for ArgumentsObject as well. As per spec, both unmapped and mapped argument objects has default @@iterator set to Array.proto.values.

Contributor guide

Tech stack
cppjavascript
Domain
performance
Issue type
performance
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
5
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
C++ proficiencyUnderstanding of JavaScript iteratorsChakraCore codebase familiarityBasic knowledge of ES6 spread operator
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
10
Research direction
Examine the existing optimization in lib/Runtime/Language/JavascriptOperators.cpp at line 1405. Understand how the check for non user defined iterator is done for JavascriptArray and TypedArrayBase. Then extend the same logic to ArgumentsObject, ensuring that the arguments object's default iterator (Array.prototype.values) is used. Consider edge cases where the arguments object might have its @@iterator overridden. Write tests to cover the optimization.
Optimize OP_LdCustomSpreadIteratorList for arguments object · chakra-core/ChakraCore#1230 | Good First Issue