mandelbrot(750) on JRuby with and without a tweaked Graal

gistfile1.txt

~/projects/graal-core $ jruby -v mandelbrot.rb 
jruby 9.1.8.0-SNAPSHOT (2.3.1) 2017-01-25 2b97d78 Java HotSpot(TM) 64-Bit Server VM 9-ea+152 on 9-ea+152 +indy +jit [linux-x86_64]
1.4988730000000001
0.875144
0.6610520000000001
0.666915
0.67083
0.658069
0.6749970000000001
0.667617
0.657871
0.674458
0.66978
0.662599
0.667123
0.658297
0.658273
0.6735150000000001
0.6749130000000001
0.664429
0.660354
0.666023

~/projects/graal-core $ JAVACMD='mx' JAVA_OPTS="vm -XX:+UseJVMCICompiler $JAVA_OPTS" jruby mandelbrot.rb 
0.960151
0.101854
0.076482
0.44248
0.09597800000000001
0.094159
0.075928
0.076088
0.076514
0.07663
0.076598
0.080044
0.07718
0.07926
0.088762
0.076311
0.076569
0.077234
0.076789
0.076705

~/projects/graal-core $ cat mandelbrot.rb 
def mandelbrot(size)
  sum = 0

  byte_acc = 0
  bit_num = 0

  y = 0
  while y < size
    ci = (2.0*y/size)-1.0

    x = 0
    while x < size
      zrzr = zr = 0.0
      zizi = zi = 0.0
      cr = (2.0*x/size)-1.5
      escape = 0b1

      z = 0
      while z < 50
        tr = zrzr - zizi + cr
        ti = 2.0*zr*zi + ci
        zr = tr
        zi = ti
        # preserve recalculation
        zrzr = zr*zr
        zizi = zi*zi
        if zrzr+zizi > 4.0
          escape = 0b0
          break
        end
        z += 1
      end

      byte_acc = (byte_acc << 1) | escape
      bit_num += 1

      # Code is very similar for these cases, but using separate blocks
      # ensures we skip the shifting when it's unnecessary, which is most cases.
      if (bit_num == 8)
        #print byte_acc.chr
        sum ^= byte_acc
        byte_acc = 0
        bit_num = 0
      elsif (x == size - 1)
        byte_acc <<= (8 - bit_num)
        #print byte_acc.chr
        sum ^= byte_acc
        byte_acc = 0
        bit_num = 0
      end
      x += 1
    end
    y += 1
  end

  sum
end

20.times {
  t = Time.now
  mandelbrot(750)
  puts Time.now - t
}