Re: Facing issues with Octave build with JIT Compiler Option

[Julien Bect]

Le 20/03/2018 à 10:02, Prasad K a écrit :
> I have successfully built the Octave 4.2.1 with JIT compiler option
> (--enable-jit). The problem seems to be with the LLVM toolkit. All the
> versions of LLVM that I tried between v3.5 to v6.0.0 have failed. The only
> version that worked for me is LLVM v3.3.

Sorry but I have mislead you with my previous email :

1) The latest changes on the JIT code were indeed meant to make it work 
with LLVM 3.8 (and perhaps 3.5 and 3.6, I should check).   But they have 
been applied to the development branch, which means that they will be 
available in Octave 4.4.x.

2) In Octave 4.2.x you still have the original JIT code written by Max 
Brister, untouched, which means that LLVM 3.3 (perhaps also 3.2 ? 3.1 ?) 
is expected as you have noticed.


If you are interested to contribute on this aspect, some work needs to 
be done to extend (in both directions !) the range of LLVM versions that 
will be supported by the next Octave release (4.4.x).


> Question: why do you want to compile with --enable-jit ?  Do you really need it 
> ?
> Ans: I have a program of simple for loop with matrix multiplication. Just
> wanted to know how much time that i can save with JIT.
>
> FYI, with LLVM v3.3, I have not found any significant difference in
> execution times with and without JIT.

Are you sure that the number of iterations is high enough to trigger the 
jit (see jit_startcnt ()) ?

Does your loop actually get jitted or not ?  You can check that using 
jit_failcnt ().

@++
Julien