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TimP
Black Belt
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XE2017u4 KNC increased vectorization threshold

I have some cases where the new update doesn't want to auto-vectorize for a correctly assessed vector speedup of 1.5x to 2.0x, so now

#if  __MIC__

!dir$ simd

#endif

(avoiding array assignment synttax) is needed to retain performance.

Similar cases for previous 2017 builds in C have been requiring conditional compilation with

#if ! __MIC__

#pragma omp simd safelen(1)

#endif

because the compiler is too aggressive when compiling for AVX2, and the update didn't require a change in source code.

Cilk plus still makes the optimum decision about vectorization of CEAN for both KNC and AVX2.

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