Re: Default configure option for JIT

[Michael D. Godfrey]

On 10/27/2013 03:38 PM, Rik wrote:
> 10/27/13
>
> One question for the 3.8 release is what to do about JIT?  Currently it is
> disabled in configure by default and one must explicitly enable it with
> '--enable-jit'.  Another option would be to enable it by default at compile
> time (and if the LLVM libraries are available), but disable it at runtime
> by setting the default value of jit_enable to false.
>
> The JIT code doesn't appear to cause any problems, and 'make check' passes
> with jit enabled or disabled.  This would suggest making it available to
> users if they want to play around with it.  On the other hand, running the
> jit.tst file under valgrind produces a segfault.  Also, even when jit is
> disabled, running under valgrind produces failing tests with 'make check'.
> This could all be the result of the valgrind environment or it might
> indicate that the JIT is doing something odd which just doesn't happen to
> occur during a normal run of 'make check'.
>
> Are there any opinions or good arguments for one approach or another?
>
> --Rik
As you know, I am a JIT fan.  The problems under valgrind are a worry, 
especially
since it is unclear what the problem is.  However, users of the release 
system,
particularly those who just get it as a package, are not going to be 
trying valgrind.
If valgrind is really finding memory allocation or other problems with 
runtime
disabled there is a more serious worry.  My experience is that I have 
for quite a while
always built with --enable-jit and turned it on in my .octaverc files. 
Some of the time
I have set the count variable to a low values so that JIT actually runs 
even on very short
loops and vectors.  I  sometimes turn debug_jit on.  I have had no 
problems.

Are the failing tests under make check just the test fails but valgrind 
does not
complain?  If so, this suggests a valgrind problem.

So, I would prefer the compile at build time ON, runtime OFF.

Michael