Intel® C++ Compiler 16.0 User and Reference Guide
Specifies a vector variant function that corresponds to its original C/C++ scalar function. This vector variant function can be invoked under vector context at call sites.
Windows* OS: __declspec(vector_variant(clauses)) |
Linux* OS: __attribute__((vector_variant(clauses))) |
clauses |
Is the following: implements clause, in the form implements (<function declarator>) [, <simd-clauses>]), where function declarator is the original scalar function, and simd-clauses is one or more of the clauses allowed for the vector attribute. The simd-clauses are optional. |
This attribute provides a means for programmers to describe the association between the vector variant function and its corresponding scalar function. The compiler will use the vector variant to replace the scalar call for a vectorized loop.
The following are restrictions for this attribute:
A vector variant function can have only one vector_variant annotation.
A vector variant annotation can have only one implements clause.
A vector variant annotation applies to only one vector variant function, which must not have both mask and nomask clauses specified. It can be specified with either mask or nomask; the default is nomask.
If the user-defined vector variant function is a variant with mask, the mask argument should be the last argument.
The following shows an example of a vector variant function:
#include<immintrin.h>
__declspec(noinline)
float MyAdd(float* a, int b) { return *a + b; }
__declspec(vector_variant(implements(MyAdd(float *a, int b)),
linear(a), vectorlength(8),
nomask, processor(future_cpu_16)))
__m256 MyAddVec(float* v_a, __m128i v_b, __m128i v_b2) {
__m256i t96 = _mm256_castsi128_si256(v_b);
__m256i tmp = _mm256_insertf128_si256(t96, v_b2, 1);
__m256 t95 = _mm256_cvtepi32_ps(tmp);
return _mm256_add_ps(*((__m256*)v_a), t95);
}
float x[2000], y[2000];
float foo(float y[]) {
#pragma omp simd
for (int k=0; k< 2000; k++) {
x[k] = MyAdd(&y[k], k);
}
return x[0] + x[1999];
}