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roberto.alfieri:pub:vectorization [13/06/2017 19:43]
roberto.alfieri
roberto.alfieri:pub:vectorization [14/06/2017 11:30]
roberto.alfieri
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 ====== Vectorization ====== ====== Vectorization ======
 +
 +[[ http://​www.training.prace-ri.eu/​uploads/​tx_pracetmo/​intel_mic_optimization.pdf | Vectorization and Code Optimization ]]
 +
  
 Processor peak performance includes the speed-up provided by the vector instructions, ​ Processor peak performance includes the speed-up provided by the vector instructions, ​
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 +
 +
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 +{{:​roberto.alfieri:​pub:​waytovectorize.png?​200|}}
 +
 +
 +
 +Auto-vectorization is the easiest and more portable way to get vectorization.
 +
 +The compiler recognize several vectiorization options.
 +
 +Main vectorization options: ​
 +
 +^     ​^ ​ Intel compiler ​  ​^  ​
 +^ KNL      | -xMIC-AVX512 ​ | 
 +^ BDW      | -xCORE-AVX2 ​  |
 +^ Disable ​ | -no-vec ​      |
 +
 +Not all loops can be vectorized:
 +
 +Some examples: ​
 +
 +  * Loop with dependencies between iterations
 +
 +<​code>​
 +for (i=1; i<MAX; i++) {
 +   d[i] = e[i] – a[i-1];
 +   a[i] = b[i] + c[i];
 +}
 +</​code>​
 +
 +
 +  * Complex loops
 +
 +  * Function calls inside the loop:
 +
 +      for (int i = 0; i < N; i++)   a[i] = foo(b[i]);
 +
 +  * Loops on data that are not aligned in memory ​   ​
 +  ​
roberto.alfieri/pub/vectorization.txt · Ultima modifica: 14/06/2017 11:30 da roberto.alfieri