clang扩展向量的三元运算符 [英] ternary operator for clang's extended vectors
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问题描述
我尝试过使用clang的扩展向量。三元运算符应该工作,但对我来说不工作。示例:
I've tried playing with clang's extended vectors. The ternary operator is supposed to work, but it is not working for me. Example:
int main()
{
using int4 = int __attribute__((ext_vector_type(4)));
int4 a{0, 1, 3, 4};
int4 b{2, 1, 4, 5};
auto const r(a - b ? a : b);
return 0;
}
请提供示例说明如何使其工作,就像< a href = http://www.informit.com/articles/article.aspx?p=1732873&seqNum=10 rel = nofollow> OpenCL 。我正在使用 clang-3.4.2
。
Please provide examples on how I might make it work, like it works under OpenCL. I am using clang-3.4.2
.
错误:
t.cpp:8:16: error: value of type 'int __attribute__((ext_vector_type(4)))' is not contextually convertible to 'bool'
auto const r(a - b ? a : b);
^~~~~
1 error generated.
推荐答案
您可以直接在Clang中遍历元素。这是针对GCC和Clang的解决方案。
You can loop over the elements directly in Clang. Here is a solution for GCC and Clang.
#include <inttypes.h>
#include <x86intrin.h>
#if defined(__clang__)
typedef float float4 __attribute__ ((ext_vector_type(4)));
typedef int int4 __attribute__ ((ext_vector_type(4)));
#else
typedef float float4 __attribute__ ((vector_size (sizeof(float)*4)));
typedef int int4 __attribute__ ((vector_size (sizeof(int)*4)));
#endif
float4 select(int4 s, float4 a, float4 b) {
float4 c;
#if defined(__GNUC__) && !defined(__INTEL_COMPILER) && !defined(__clang__)
c = s ? a : b;
#else
for(int i=0; i<4; i++) c[i] = s[i] ? a[i] : b[i];
#endif
return c;
}
两者都会产生
select(int __vector(4), float __vector(4), float __vector(4)):
pxor xmm3, xmm3
pcmpeqd xmm0, xmm3
blendvps xmm1, xmm2, xmm0
movaps xmm0, xmm1
ret
- Nehalem: https://godbolt.org/g/cVWYym
- Skylake: https://godbolt.org/g/LhEpnN
- KNL: https://godbolt.org/g/NFrFKg
- Nehalem: https://godbolt.org/g/cVWYym
- Skylake: https://godbolt.org/g/LhEpnN
- KNL: https://godbolt.org/g/NFrFKg
但是使用AVX512最好使用掩码(例如 __ mmask16
)
But with AVX512 it's better to use masks (e.g. __mmask16
).
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