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

[Eliot Miranda]

> 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