Commits on Oct 23, 2023

1. [JSC] ForStatement should call CreatePerIterationEnvironment before f… …

   …irst iteration
   
   https://bugs.webkit.org/show_bug.cgi?id=189799
   <rdar://problem/44730906>
   
   Reviewed by Justin Michaud.
   
   This change implements step 2 of ForBodyEvaluation [1], but only if loop initializer contains a function
   that captures a variable from outer scope (so-called closure), to preserve performance of the common case.
   
   Emitting prepareLexicalScopeForNextForLoopIteration() unconditionally would otherwise slow down any `for`
   loop with body statement containing a closure (which is a quite common) by 10-20%.
   
   Before this patch, a closure inside `for` loop initializer was created with parent scope of the first
   iteration, rather than a separate lexical scope, ending up capturing incorrect loop counter value.
   
   Aligns JSC with V8 and SpiderMonkey.
   
   [1]: https://tc39.es/ecma262/#sec-forbodyevaluation
   
   * JSTests/stress/regress-189799.js: Added.
   * JSTests/test262/expectations.yaml: Mark 2 tests as passing.
   * Source/JavaScriptCore/bytecompiler/NodesCodegen.cpp:
   (JSC::ForNode::emitBytecode):
   * Source/JavaScriptCore/parser/ASTBuilder.h:
   (JSC::ASTBuilder::createForLoop):
   * Source/JavaScriptCore/parser/NodeConstructors.h:
   (JSC::ForNode::ForNode):
   * Source/JavaScriptCore/parser/Nodes.h:
   * Source/JavaScriptCore/parser/Parser.cpp:
   (JSC::Parser<LexerType>::parseForStatement):
   * Source/JavaScriptCore/parser/SyntaxChecker.h:
   (JSC::SyntaxChecker::createForLoop):
   
   Canonical link: https://commits.webkit.org/269653@main

   Alexey Shvayka committed Oct 23, 2023
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