Bug 157775 – [JSC] "return this" in a constructor does not need a branch on isObject(this)

• Component: New Bugs
• Status: RESOLVED FIXED

[Benjamin Poulain]

[JSC] "return this" in a constructor does not need a branch on isObject(this)

[Benjamin Poulain]

Created attachment 279073 [details]
Patch

[Benjamin Poulain]

                                    Conf#1                    Conf#2                                      

3d-cube                         4.9549+-0.0261     ?      4.9916+-0.0312        ?
3d-morph                        5.0523+-0.0255     ?      5.0780+-0.0304        ?
3d-raytrace                     5.3399+-0.0310            5.3223+-0.0249        
access-binary-trees             2.0966+-0.0164     ^      2.0264+-0.0164        ^ definitely 1.0346x faster
access-fannkuch                 5.8749+-0.0359     ^      5.8014+-0.0308        ^ definitely 1.0127x faster
access-nbody                    2.5241+-0.0162     ?      2.5462+-0.0184        ?
access-nsieve                   2.9690+-0.0152            2.9677+-0.0163        
bitops-3bit-bits-in-byte        1.0807+-0.0084     ?      1.0826+-0.0085        ?
bitops-bits-in-byte             2.7130+-0.0180     ?      2.7253+-0.0201        ?
bitops-bitwise-and              2.0030+-0.0133            1.9902+-0.0108        
bitops-nsieve-bits              3.0466+-0.0198     ?      3.0540+-0.0238        ?
controlflow-recursive           2.3161+-0.0152     ?      2.3349+-0.0179        ?
crypto-aes                      4.4217+-0.0372            4.4038+-0.0318        
crypto-md5                      2.4412+-0.0167            2.4099+-0.0157          might be 1.0130x faster
crypto-sha1                     2.2903+-0.0174     ?      2.2995+-0.0180        ?
date-format-tofte               6.6671+-0.0416            6.6478+-0.0401        
date-format-xparb               4.8312+-0.0372            4.8075+-0.0361        
math-cordic                     2.8409+-0.0129     ?      2.8411+-0.0168        ?
math-partial-sums               4.2179+-0.0366            4.2139+-0.0341        
math-spectral-norm              1.9951+-0.0155            1.9880+-0.0119        
regexp-dna                      6.5850+-0.0456     ?      6.6112+-0.0548        ?
string-base64                   4.2546+-0.0384            4.2394+-0.0342        
string-fasta                    5.6429+-0.0195            5.6271+-0.0216        
string-tagcloud                 8.6104+-0.0471     ?      8.6181+-0.0574        ?
string-unpack-code             18.7322+-0.1295           18.5419+-0.1163          might be 1.0103x faster
string-validate-input           4.1828+-0.0290     ?      4.1885+-0.0282        ?

<arithmetic>                    4.5263+-0.0071            4.5138+-0.0073          might be 1.0028x faster

[Saam Barati]

Comment on attachment 279073 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=279073&action=review

> Source/JavaScriptCore/bytecompiler/BytecodeGenerator.cpp:3223
> +        bool shouldEmitIsObjectTest = derived || !srcIsThis;

I think that if you're in an ES6 derived constructor, your 'this' value must either be TDZ or an object.
I'm fairly sure then that 'shouldEmitIsObjectTest' can just be !srcIsThis because the TDZ check
above will cover 'this' being TDZ.

[Benjamin Poulain]

Created attachment 279085 [details]
Patch

[Saam Barati]

Comment on attachment 279085 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=279085&action=review

> Source/JavaScriptCore/bytecompiler/BytecodeGenerator.cpp:3232
>                  emitTDZCheck(&m_thisRegister);

This can be:
if (!srcIsThis)
    emitTDZCheck...

[Saam Barati]

Comment on attachment 279085 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=279085&action=review

>> Source/JavaScriptCore/bytecompiler/BytecodeGenerator.cpp:3232
>>                  emitTDZCheck(&m_thisRegister);
> 
> This can be:
> if (!srcIsThis)
>     emitTDZCheck...

Oh. Never mind

[Benjamin Poulain]

Created attachment 279087 [details]
Patch for landing

[WebKit Commit Bot]

Comment on attachment 279087 [details]
Patch for landing

Clearing flags on attachment: 279087

Committed r200992: <http://trac.webkit.org/changeset/200992>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.