606879 - TM: some double values should be integers in audio-fft

Status: RESOLVED WONTFIX

(Core :: JavaScript Engine, defect)

Description

[Nicholas Nethercote [inactive]]

The hottest loop in audio-fft looks like this:

      while ( i < bufferSize ) {
        off = i + halfSize;
        tr = (currentPhaseShiftReal * real[off]) - (currentPhaseShiftImag * imag
[off]);
        ti = (currentPhaseShiftReal * imag[off]) + (currentPhaseShiftImag * real
[off]);

        real[off] = real[i] - tr;
        imag[off] = imag[i] - ti;
        real[i] += tr;
        imag[i] += ti;

        i += halfSize << 1;
      }

'i' and 'halfSize' are loaded as doubles.  The result is that 'i' and 'off' have to be converted to integers with code like this:

      d2i2 = d2i $stack13
      i2d2 = i2d d2i2
      eqd2 = eqd $stack13, i2d2
      xf9: xf eqd2 -> pc=0x93a8687 imacpc=(nil) sp+32 rp+0 (GuardID=019)

and halfSize has to be converted with a call to js_DoubleToInt32().

I'm not sure why these variables are treated as doubles.  The only double-ish use I can see is that 'i' is assigned like this elsewhere:

  i = bufferSize/2;

Maybe that's the problem.

If we can fix this I roughly estimate a 5--10% speedup based on Cachegrind numbers.  audio-beat-detection will be sped up similarly because it's practically identical to audio-fft (see bug 603837).

Comment 1

[Nicholas Nethercote [inactive]]

The stability info at the end of this fragment looks like this:

Stability of fragment 0x93075a4:
ENTRY STACK=FOONOIOOOOOOIIIIDIIIDDUI GLOBALS=OOFO
Stability of fragment 0x937729c:
ENTRY STACK=FOONODOOOOOODDDDDDDDDDDD GLOBALS=OOFO
Stability of fragment 0x934211c:
ENTRY STACK=FOONODOOOOOODDDDDDDDDDUD GLOBALS=OOFO
Stability of fragment 0x93da404:
ENTRY STACK=FOONODOOOOOODDDDDDDUUUUD GLOBALS=OOFO
Stability of fragment 0x931c3cc:
ENTRY STACK=FOONOIOOOOOOIIIDDDDIDDDI GLOBALS=OOFO
Stability of fragment 0x93198e4:
ENTRY STACK=FOONOIOOOOOOIIIDDDIIDDDI GLOBALS=OOFO
Stability of fragment 0x9316d94:
ENTRY STACK=FOONOIOOOOOOIIIDDDDIDDII GLOBALS=OOFO
Stability of fragment 0x93142bc:
ENTRY STACK=FOONOIOOOOOOIIIDDIIIDDDI GLOBALS=OOFO
Stability of fragment 0x931174c:
ENTRY STACK=FOONOIOOOOOOIIIDIDIIDDII GLOBALS=OOFO
Stability of fragment 0x930ebfc:
ENTRY STACK=FOONOIOOOOOOIIIDIIIIDDII GLOBALS=OOFO
Recording completed at  /home/njn/moz/kraken-njn/tests/kraken-1.0/audio-fft-data.js:334@287 via closeLoop (FragID=000029)

Presumably this is relevant;  I don't yet understand how stack variables have types assigned.

Comment 2

[Nicholas Nethercote [inactive]]

TM's days are numbered:  WONTFIX.