[Webkit-unassigned] [Bug 192496] Enable DFG on ARM/Linux again

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Mon Dec 10 05:26:59 PST 2018


https://bugs.webkit.org/show_bug.cgi?id=192496

--- Comment #7 from Dominik Inf├╝hr <dinfuehr at igalia.com> ---
Comment on attachment 356800
  --> https://bugs.webkit.org/attachment.cgi?id=356800
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=356800&action=review

Thanks for taking a look at the patch! I agree, I should definitely add some more comments for that. I will certainly add them, when you agree with the approaches I took. Again, thanks for your time!

>> Source/JavaScriptCore/ChangeLog:10
>> +        in compiled DFG code.
> 
> Please describe why r11 is avoided.

True, I should definitely document that. I don't use it, since r11 is used as callee-saved register for metadataTable in LLInt.

>> Source/JavaScriptCore/dfg/DFGOSRExit.cpp:143
>> +#endif
> 
> Why?

I avoided to implement this since we don't have callee-saved floating-point registers on 32-bit architectures yet. AFAIU implementing this might be a bit complicated since general-purpose register are 32-bit wide for 32-bit architectures, while floating point registers are 64-bit wide.

>> Source/JavaScriptCore/jit/CallFrameShuffler.cpp:58
>> +#endif
> 
> Why?

RegisterSet::vmCalleeSaveRegisters() used to be the empty set on 32-bit architectures, now on ARM this returns r11 (so the metadataTable register). So the register r11 would be used by CallFrameShuffler and therefore needs to be saved/restored, it seemed the simplest to just avoid using this register in here. RegisterSet::vmCalleeSaveRegisters() used to be the empty set, so there shouldn't be fewer register available than before.

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