[Webkit-unassigned] [Bug 170089] [jsc][mips] Add missing MacroAssembler functions after r214187

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Tue Apr 11 05:16:16 PDT 2017


Yusuke Suzuki <utatane.tea at gmail.com> changed:

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--- Comment #7 from Yusuke Suzuki <utatane.tea at gmail.com> ---
Comment on attachment 305523
  --> https://bugs.webkit.org/attachment.cgi?id=305523

View in context: https://bugs.webkit.org/attachment.cgi?id=305523&action=review

>>>> Source/JavaScriptCore/assembler/MacroAssemblerMIPS.h:2462
>>>> +    }
>>> Looking the loadDouble code, we can see WTF_MIPS_ISA(1) guard.
>>> Isn't it required here?
>> I think Yusuke is right. FPRegisterIDs refer to 64-bit registers. In
>> MIPS32/MIPS-II “ldc1” can be used to load a 32-bit value directly,
>> but in MIPS-I it is needed to use two “lwc1” instructions, one for
>> each 32-bit half of the 64-bit value.
> No, I don't think we need that guard. loadDouble/storeDouble use that because MIPS-I does not contain the ldc1 (resp. sdc1) instruction, and therefore two lwc1 (resp swc1) instructions are used instead for the MIPS-I version. In loadFloat/storeFloat, we do not use ldc1/sdc1, and all the instructions that we use are MIPS-I compatible AFAIK, so there's no need for an alternative version.
> You can see that the pre-existing loadFloat/storeFloat with a BaseIndex argument don't have such a guard either, for the same reasons.
> Another way to put it: the need for special cases for MIPS-I only exists when dealing with doubles. The fact of using an ImplicitAddress instead of a BaseIndex does not incur this need. 
> Another debate is whether we still want to support MIPS-I, I don't know if there still are many devices using that where it makes sense to use webkit, though I could be wrong, because, hey, we have these guards in the code.

Make sense.

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