[Vm-dev] Funny Floats [WAS OpenSmalltalk current on aarch64]

[tesonep at gmail.com]

Hi Eliot, you can use PT as initials (I don't if there is a clash or
ptesone) and the timestamp is just today.

Thanks

On Wed, Dec 11, 2019 at 6:02 PM Eliot Miranda <eliot.miranda at gmail.com> wrote:
>
>
>
>
> > On Dec 11, 2019, at 8:45 AM, "tesonep at gmail.com" <tesonep at gmail.com> wrote:
> >
> > 
> > Hi Ken,
> > this is a problem in an optimization of GCC 8.3 (I am not sure what
> > other versions are impacted).
> > Basically it is generating bad a function, removing code that assumes
> > that is dead code.
> > Even though this is a bug in GCC, because there is not actual reason
> > to remove the code.
> > It is produced because the code is not written in a nice way.
> >
> > Basically, if someone wants to fix it in the VM code is modifying a
> > single method:
> >
> > Spur64BitMemoryManager >> fetchLong32: fieldIndex ofFloatObject: oop
> >    "index by word size, and return a pointer as long as the word size"
> >
> >    | bits |
> >    (self isImmediateFloat: oop) ifFalse:
> >        [^self fetchLong32: fieldIndex ofObject: oop].
> >    bits := self smallFloatBitsOf: oop.
> >    ^ fieldIndex = 0
> >        ifTrue: [bits bitAnd: 16rFFFFFFFF]
> >        ifFalse: [bits >> 32]
>
> Thank you, Pablo.  I’ll integrate this quickly.  Can you possibly give me initials and time stamp?  It’s not necessary but helps that the code is marked as being your fix.
>
> >
> > The old method had a handwritten piece of C code to replace the last if:
> >
> > (self cCoerceSimple: (self addressOf: bits) to: #'int *') at: fieldIndex
> >
> > I assume it was done to handle a different kind of endianness, but the
> > single sender of this message is already doing the handling and having
> > different behavior depending on the endianness.
> >
> > With this fix the build can still be executed with -O2 optimization in GCC 8.3
> >
> > Cheers,
> >
> >> On Sat, Dec 7, 2019 at 4:20 PM <ken.dickey at whidbey.com> wrote:
> >>
> >>
> >>> Have you tried switching off compiler optimisations?
> >>
> >> Ah!  I had forgotten that one.  I thought that was changed in mvm.
> >>
> >> Image works fine noe (but more slowly!) on aarch64 Alpine Linux
> >> (musl+busybox).
> >>
> >> I am just out the door fir a couple of days but will try fdlib on
> >> return.
> >>
> >> Thanks again to all!
> >> -KenD
> >
> >
> >
> > --
> > Pablo Tesone.
> > tesonep at gmail.com



-- 
Pablo Tesone.
tesonep at gmail.com