[Vm-dev] ARM Cog progress

Ryan Macnak rmacnak at gmail.com
Tue Jun 9 02:54:19 UTC 2015


On Sun, Jun 7, 2015 at 8:58 AM, tim Rowledge <tim at rowledge.org> wrote:

>
>
> On 07-06-2015, at 12:32 AM, Holger Freyther <holger at freyther.de> wrote:
> >> On 07 Jun 2015, at 01:25, tim Rowledge <tim at rowledge.org> wrote:
> >>
> >>
> >> GCC is such fun.
> >
> > given the amount of warnings emitted during compilation, have you
> considered
> > that it might be the input given to gcc that is the issue here? ;)
>
> I dunno; I get a total of 59 warnings when compiling the ARM Cog VM, none
> in the core vm code. I’d love to see it be 0. I rather suspect the world
> would come to an end if that happened.
>
> On the other hand, I can’t see how it is acceptable for a compiler to
> produce code that blows up at one level of optimisation but not at another.
> Come to that I’m not sure why there are different levels; I can sort of see
> asking to optimise in different ways  - the NorCroft compiler for ARM can
> be asked to optimise for runtime speed or executable size, for example.
>

I'm inclined to believe Cog is relying on undefined behavior somewhere, and
this isn't gcc's fault. I've not built functional Newspeak VMs on modern
compilers since ~1317, but this overlaps with the VM being broken on old
compilers for other reasons so I haven't figured out what change is
responsible.
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