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<b><a class="bz_bug_link
bz_status_NEW "
title="NEW - [ES6] Arrow function syntax. Emit loading&putting this/super only if they are used in arrow function"
href="https://bugs.webkit.org/show_bug.cgi?id=153981#c3">Comment # 3</a>
on <a class="bz_bug_link
bz_status_NEW "
title="NEW - [ES6] Arrow function syntax. Emit loading&putting this/super only if they are used in arrow function"
href="https://bugs.webkit.org/show_bug.cgi?id=153981">bug 153981</a>
from <span class="vcard"><a class="email" href="mailto:sbarati@apple.com" title="Saam Barati <sbarati@apple.com>"> <span class="fn">Saam Barati</span></a>
</span></b>
<pre>Comment on <span class=""><a href="attachment.cgi?id=271327&action=diff" name="attach_271327" title="Patch">attachment 271327</a> <a href="attachment.cgi?id=271327&action=edit" title="Patch">[details]</a></span>
Patch
View in context: <a href="https://bugs.webkit.org/attachment.cgi?id=271327&action=review">https://bugs.webkit.org/attachment.cgi?id=271327&action=review</a>
LGTM, just a few design suggestions and renaming suggestions.
Have you run perf numbers?
<span class="quote">> Source/JavaScriptCore/bytecode/UnlinkedCodeBlock.h:132
> + bool isInnerArrowFunctionUseArguments() { return m_arrowFunctionCodeFeatures & ArgumentsArrowFunctionFeature; }
> + bool isInnerArrowFunctionUseSuperCall() { return m_arrowFunctionCodeFeatures & SuperCallArrowFunctionFeature; }
> + bool isInnerArrowFunctionUseSuperProperty() { return m_arrowFunctionCodeFeatures & SuperPropertyArrowFunctionFeature; }
> + bool isInnerArrowFunctionUseEval() { return m_arrowFunctionCodeFeatures & EvalArrowFunctionFeature; }
> + bool isInnerArrowFunctionUseThis() { return m_arrowFunctionCodeFeatures & ThisArrowFunctionFeature; }
> + bool isInnerArrowFunctionUseNewTarget() { return m_arrowFunctionCodeFeatures & NewTargetArrowFunctionFeature; }</span >
I would name these like "doAnyInnerArrowFunctionsX"
i.e:
isInnerArrowFunctionUseArguments => doAnyInnerArrowFunctionsUseArguments
<span class="quote">> Source/JavaScriptCore/bytecompiler/BytecodeGenerator.cpp:4051
> +bool BytecodeGenerator::isNewTargetUsedInArrowFunction()
> +{
> + return m_codeBlock->isInnerArrowFunctionUseNewTarget() || m_codeBlock->isInnerArrowFunctionUseSuperCall();
> +}</span >
Is "new.target" not allowed in eval?
<span class="quote">> Source/JavaScriptCore/bytecompiler/BytecodeGenerator.h:648
> + void emitPutThisToArrowFunctionContextScope(bool = false);</span >
Style: give this bool a name, like "shouldAlwaysPut" or something.
<span class="quote">> Source/JavaScriptCore/bytecompiler/BytecodeGenerator.h:724
> + bool isThisUsedInArrowFunction();
> + bool isNewTargetUsedInArrowFunction();
> + bool isSuperUsedInArrowFunction();
> + bool isArgumentsUsedInArrowFunction();</span >
nit: I would name these with "Inner" before "In"
like:
"isThisUsedInInnerArrowFunction"
<span class="quote">> Source/JavaScriptCore/bytecompiler/NodesCodegen.cpp:764
> + generator.emitPutThisToArrowFunctionContextScope(true);</span >
Style: We usually write code like this by assigning the boolean as a local variable and passing the local variable to the function:
```
bool forcePutToScope = true;
generator.emitPutThisToArrowFunctionContextScope(forcePutToScope);
```
<span class="quote">> Source/JavaScriptCore/parser/Parser.cpp:2067
> + if (functionBodyType != StandardFunctionBodyBlock)
> + closestParentNonArrowFunctionNonLexicalScope()->setInnerArrowFunctionUseSuperCall();</span >
An alternative to repeatedly doing a scope search here is to just propagate this information
when we pop the scope. That's usually how we propagate information upwards. Look at popScopeInternal.
Also, instead of "functionBodyType != StandardFunctionBodyBlock", I think the code is easier to read
with affirmative conditions, like "bodyType == ArrowExpr || bodyType == ArrowBlock"
<span class="quote">> Source/JavaScriptCore/parser/Parser.cpp:3644
> + if (m_vm->propertyNames->eval == *ident)
> + closestParentNonArrowFunctionNonLexicalScope()->setInnerArrowFunctionUseEval();
> + else if (m_vm->propertyNames->arguments == *ident)
> + closestParentNonArrowFunctionNonLexicalScope()->setInnerArrowFunctionUseArgumetns();</span >
If you go with the popScopeInternalApproach, this can be determined then as well when we're already iterating over all used variables.
<span class="quote">> Source/JavaScriptCore/parser/ParserModes.h:164
> +typedef uint16_t ArrowFunctionCodeFeatures;</span >
this can be uint8_t
<span class="quote">> Source/JavaScriptCore/parser/SourceProviderCacheItem.h:47
> + unsigned innerArrowFunctionFeatures;</span >
Why not ArrowFunctionCodeFeatures instead of unsigned?
<span class="quote">> Source/JavaScriptCore/parser/SourceProviderCacheItem.h:92
> + unsigned innerArrowFunctionFeatures : 31;</span >
ditto.</pre>
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