Re: Safety of enabling JIT

[John W. Eaton]

On 12/09/2013 12:10 AM, Rik wrote:
> On 12/08/2013 10:00 AM, address@hidden wrote:
> > Message: 2
> > Date: Sun, 8 Dec 2013 00:33:14 +0200
> > From: Susi Lehtola <address@hidden>
> > To: Octave Maintainers List <address@hidden>
> > Subject: Safety of enabling JIT
> > Message-ID: <address@hidden>
> > Content-Type: text/plain; charset=US-ASCII
> >
> > Hi,
> >
> >
> > configure reports
> >    --enable-jit            (EXPERIMENTAL) enable JIT compiler
> > but this seems to be the default when llvm is available.
> >
> > How safe is the option nowadays?
>
> It *seems* safe.  First, even when the JIT compiler is built (configure
> time decision) the compiler is not enabled at runtime.  To do so a user
> either needs to invoke octave with the option --jit-compiler or use
> "enable_jit (1)" from within Octave.  Second, there are a series of JIT
> verification tests and they all pass.  The only contra-indication has been
> some memory leaks and weirdness when running JIT under valgrind.  Although
> this may point to a problem, it has never manifested itself in normal
> operation.  It might just be something about the valgrind environment.
> >   Can we enable it for the Fedora
> > package?
> I think so, for the reasons above.

If we are going to recommend enabling it, then I think we should make 
that the default.

I still think the JIT compiler should be disabled by default, and we 
need to be sure that enabling the code but not running it doesn't cause 
any trouble.

Does linking with the LLVM libraries cause any trouble for Octave?

When it is disabled at run time, we are sure it doesn't have any effect 
on Octave?

I don't normally build with it, so I don't know.

jwe