[PATCH] jscript: Force base type of _jsval_t to be ULONGLONG instead of double.

[Dmitry Timoshkov]

Jacek Caban <jacek at codeweavers.com> wrote:

> Hi Dmitry,
> 
> On 4/2/21 8:19 AM, Dmitry Timoshkov wrote:
> > Hi Jacek,
> > 
> > Jacek Caban <jacek at codeweavers.com> wrote:
> > 
> >>>>> Gabriel Ivăncescu <gabrielopcode at gmail.com> wrote:
> >>>>>
> >>>>>> Looks like a bug in Clang to me, although working around it is fine, but
> >>>>>> it's not my call.
> >>>>>>
> >>>>>> Nevertheless I think you should report it to Clang so they fix it.
> >>>>> Why do you think that it's a clang bug? Using fldl + fstpl to store and
> >>>>> fetch the double to/from the floating point stack is perfectly legitimate.
> >>>>>
> >>>> Well, because jsval_t is a union, not a double. Shouldn't assignment be
> >>>> a bitwise copy? The compiler can't know what actual type is used by the
> >>>> union here. Unless I misremember the C standard.
> >>> If I understand correctly, the compiler have chosen the memeber of
> >>> a maximal bits width and used it for a copy. That's unfortunate that
> >>> the chosen member happened to be of type 'double', and as a result
> >>> floating point instructions were used to perform the copying operation.
> >>
> >>
> >> Compiler is free to use any copy implementation it wants, but it can't
> >> affect stored values. If it changes stored values, it's obviously a
> >> compiler bug. But it would be good to understand what's exactly going on
> >> before jumping to that conclusion. From your description, I don't yet
> >> see the exact problem. I also can't reproduce it with my builds. Could
> >> you please send me your jscript.dll build?
> > 
> > Did you find anything useful in jscript.dll that I sent you?
> 
> The good news is that I managed to reproduce it locally, so I could 
> experiment with it. I'm leaning towards a solution like (a cleaner 
> version of) the attached patch. It fixes the problem for me. I'm not yet 
> sure about that, it needs another look, but it would be interesting to 
> confirm that it works for you.

The patch works. Thanks!

-- 
Dmitry.