implict SIMD (SSE/AVX) broadcasts with GCC
avx, gcc, simd, sse
Solution
I think there is currently no direct way and you have to work around it using the syntax you already noticed:
__m256 zero={};
__m256 x=zero+3.14159f;
It may change in the future if we can agree on a good syntax, see PR 55726.
Note that if you want to create a vector `{ s, s, ... s }` with a non-constant `float s`, the technique above only works with integers, or with floats and `-fno-signed-zeros`. You can tweak it to `__m256 x=s-zero;` and it will work unless you use `-frounding-math`. A last version, suggested by Z boson, is `__m256 x=(zero+1.f)*s;` which should work in most cases (except possibly with a compiler paranoid about sNaN).
Problem
I have manged to convert most of my SIMD code to us the vector extensions of GCC. However, I have not found a good solution for doing a broadcast as follows ``` __m256 areg0 = _mm256_broadcast_ss(&a[i]); ``` I want to do ``` __m256 argeg0 = a[i]; ``` If you see my answer at Mutiplying vector by constant using SSE I managed to get broadcasts working with another SIMD register. The following works: ``` __m256 x,y; y = x + 3.14159f; // broadcast x + 3.14159 y = 3.14159f*x; // broadcast 3.14159*x ``` but this won't work: ``` __m256 x; x = 3.14159f; //should broadcast 3.14159 but does not work ``` How can I do this with GCC?