(octave.info)JIT Compiler

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19.5 JIT Compiler
=================

Vectorization is the preferred technique for eliminating loops and
speeding up code.  Nevertheless, it is not always possible to replace
every loop.  In such situations it may be worth trying Octave’s
*experimental* Just-In-Time (JIT) compiler.

   A JIT compiler works by analyzing the body of a loop, translating the
Octave statements into another language, compiling the new code segment
into an executable, and then running the executable and collecting any
results.  The process is not simple and there is a significant amount of
work to perform for each step.  It can still make sense, however, if the
number of loop iterations is large.  Because Octave is an interpreted
language every time through a loop Octave must parse the statements in
the loop body before executing them.  With a JIT compiler this is done
just once when the body is translated to another language.

   The JIT compiler is a very new feature in Octave and not all valid
Octave statements can currently be accelerated.  However, if no other
technique is available it may be worth benchmarking the code with JIT
enabled.  The function ‘jit_enable’ is used to turn compilation on or
off.  The function ‘jit_startcnt’ sets the threshold for acceleration.
Loops with iteration counts above ‘jit_startcnt’ will be accelerated.
The functions ‘jit_failcnt’ and ‘debug_jit’ are not likely to be of use
to anyone not working directly on the implementation of the JIT
compiler.

 -- : VAL = jit_enable ()
 -- : OLD_VAL = jit_enable (NEW_VAL)
 -- : jit_enable (NEW_VAL, "local")
     Query or set the internal variable that enables Octave’s JIT
     compiler.

     When called from inside a function with the "local" option, the
     variable is changed locally for the function and any subroutines it
     calls.  The original variable value is restored when exiting the
     function.

     See also: Note: jit_startcnt, *note debug_jit:
     XREFdebug_jit.

 -- : VAL = jit_startcnt ()
 -- : OLD_VAL = jit_startcnt (NEW_VAL)
 -- : jit_startcnt (NEW_VAL, "local")
     Query or set the internal variable that determines whether JIT
     compilation will take place for a specific loop.

     Because compilation is a costly operation it does not make sense to
     employ JIT when the loop count is low.  By default only loops with
     greater than 1000 iterations will be accelerated.

     When called from inside a function with the "local" option, the
     variable is changed locally for the function and any subroutines it
     calls.  The original variable value is restored when exiting the
     function.

     See also: Note: jit_enable, *note jit_failcnt:
     XREFjit_failcnt, Note: debug_jit.

 -- : VAL = jit_failcnt ()
 -- : OLD_VAL = jit_failcnt (NEW_VAL)
 -- : jit_failcnt (NEW_VAL, "local")
     Query or set the internal variable that counts the number of JIT
     fail exceptions for Octave’s JIT compiler.

     When called from inside a function with the "local" option, the
     variable is changed locally for the function and any subroutines it
     calls.  The original variable value is restored when exiting the
     function.

     See also: Note: jit_enable, *note jit_startcnt:
     XREFjit_startcnt, Note: debug_jit.

 -- : VAL = debug_jit ()
 -- : OLD_VAL = debug_jit (NEW_VAL)
 -- : debug_jit (NEW_VAL, "local")
     Query or set the internal variable that determines whether
     debugging/tracing is enabled for Octave’s JIT compiler.

     When called from inside a function with the "local" option, the
     variable is changed locally for the function and any subroutines it
     calls.  The original variable value is restored when exiting the
     function.

     See also: Note: jit_enable, *note jit_startcnt:
     XREFjit_startcnt.