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    <p>To address some of the scepticism expressed by others here I suggest anyone who wants to prove to themselves or other use the following method:</p> <ul> <li>Create a JMH project</li> <li>Write a small snippet of vectorizable math.</li> <li>Run their benchmark flipping between -XX:-UseSuperWord and -XX:+UseSuperWord(default)</li> <li>If no difference in performance is observed, your code probably didn't get vectorized</li> <li>To make sure, run your benchmark such that it prints out the assembly. On linux you can enjoy the perfasm profiler('-prof perfasm') have a look and see if the instructions you expect get generated.</li> </ul> <p>Example:</p> <pre><code>@Benchmark @CompilerControl(CompilerControl.Mode.DONT_INLINE) //makes looking at assembly easier public void inc() { for (int i=0;i&lt;a.length;i++) a[i]++;// a is an int[], I benchmarked with size 32K } </code></pre> <p>The result with and without the flag (on recent Haswell laptop, Oracle JDK 8u60): -XX:+UseSuperWord : 475.073 ± 44.579 ns/op (nanoseconds per op) -XX:-UseSuperWord : 3376.364 ± 233.211 ns/op</p> <p>The assembly for the hot loop is a bit much to format and stick in here but here's a snippet(hsdis.so is failing to format some of the AVX2 vector instructions so I ran with -XX:UseAVX=1): -XX:+UseSuperWord(with '-prof perfasm:intelSyntax=true')</p> <pre><code> 9.15% 10.90% │││ │↗ 0x00007fc09d1ece60: vmovdqu xmm1,XMMWORD PTR [r10+r9*4+0x18] 10.63% 9.78% │││ ││ 0x00007fc09d1ece67: vpaddd xmm1,xmm1,xmm0 12.47% 12.67% │││ ││ 0x00007fc09d1ece6b: movsxd r11,r9d 8.54% 7.82% │││ ││ 0x00007fc09d1ece6e: vmovdqu xmm2,XMMWORD PTR [r10+r11*4+0x28] │││ ││ ;*iaload │││ ││ ; - psy.lob.saw.VectorMath::inc@17 (line 45) 10.68% 10.36% │││ ││ 0x00007fc09d1ece75: vmovdqu XMMWORD PTR [r10+r9*4+0x18],xmm1 10.65% 10.44% │││ ││ 0x00007fc09d1ece7c: vpaddd xmm1,xmm2,xmm0 10.11% 11.94% │││ ││ 0x00007fc09d1ece80: vmovdqu XMMWORD PTR [r10+r11*4+0x28],xmm1 │││ ││ ;*iastore │││ ││ ; - psy.lob.saw.VectorMath::inc@20 (line 45) 11.19% 12.65% │││ ││ 0x00007fc09d1ece87: add r9d,0x8 ;*iinc │││ ││ ; - psy.lob.saw.VectorMath::inc@21 (line 44) 8.38% 9.50% │││ ││ 0x00007fc09d1ece8b: cmp r9d,ecx │││ │╰ 0x00007fc09d1ece8e: jl 0x00007fc09d1ece60 ;*if_icmpge </code></pre> <p>Have fun storming the castle!</p>
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    1. PODo any JVM's JIT compilers generate code that uses vectorized floating point instructions?
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