[Webkit-unassigned] [Bug 169714] [jsc] Add missing MacroAssemblerMIPS::or32() implementation

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Thu Apr 6 16:08:14 PDT 2017


https://bugs.webkit.org/show_bug.cgi?id=169714

--- Comment #3 from Guillaume Emont <guijemont at igalia.com> ---
(In reply to Adrian Perez from comment #2)
> Comment on attachment 304573 [details]
> Patch
> 
> View in context:
> https://bugs.webkit.org/attachment.cgi?id=304573&action=review
> 
> Reviewing informally: The comparisons should treat immediate value
> zero as a 16-bit value which gets embedded in an “ori” instruction.
> Other than that looks good overall.
> 
> There is the thing that I would prefer using constants from “stdint.h” or
> masking with 0xFFFF to check for values outside of the 16-bit range, but
> the rest of the code in the file compares directly against the numeric
> values, so I don't have a strong feeling about that. It might be a good
> idea to do change the code to use [U]INTx_{MIN,MAX} or bitmaks, as a
> separate patch. WDYT?
> 
> > Source/JavaScriptCore/assembler/MacroAssemblerMIPS.h:448
> > +        if (address.offset >= -32768 && address.offset <= 32767
> 
> Personally, I would write this condition as...
> 
>       if (address.offset & 0xFFFF == 0 && ...)
> 
> ...because when reading this form it makes me think “this checks whether
> the upper 16-bits are unset”. On the other hand, comparisons against the
> integral values keep me wondering “wait, why is there a magic number here?”.
> 
> I have no strong opinion about whether to use the bitmask version or the
> integer comparison, but if you would rather keep the integer comparison,
> please use INT16_MIN/INT16_MAX, which makes it more explicit that values
> outside the 16-bit integer range are being handled:
> 
>        if (address.offset >= INT16_MIN && address.offset <= INT16_MAX && ...)
> 
Indeed, this would be clearer, especially with the bitmask I'd think. I'll create a separate bug and try to address that for the whole file.


> > Source/JavaScriptCore/assembler/MacroAssemblerMIPS.h:457
> > +            if (imm.m_value > 0 && imm.m_value <= 65535 && !m_fixedWidth)
> 
> This should be “greater or equal to zero”, not just ”greater than zero”:
> 
>      if (imm.m_value >= 0 && imm.m_value <= UINT16_MAX ...)
>   or if (imm.m_value & 0xFFFF == 0 ...)
> 
> If the immediate value is equal to zero, emitting the code for ORing
> could even be skipped altogether. Though I would do that separately
> on another patch.
I am cooking a patch that address this issues. Here again, I just copy-pasted from another version of the function, and that issue is a bit everywhere in the file and deserves its own bug I guess.

> 
> > Source/JavaScriptCore/assembler/MacroAssemblerMIPS.h:477
> > +            if (imm.m_value > 0 && imm.m_value <= 65535 && !m_fixedWidth)
> 
> Ditto: if (imm.m_value >= 0 && imm.m_value <= UINT16_MAX ...)
>                        ^^
>                  greater or equal

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