copysignf intrinsic

;; Source code, avoids constant propagation

;;#include <math.h>
;;extern volatile float place, a, b;
;;__attribute__((noinline))
;;void foo() { place = copysignf(a, b); }

;; GCC 8.2, -O3 -march=skylake -c -ffast-math
foo():
        vmovss  xmm1, DWORD PTR b[rip]
        vmovss  xmm0, DWORD PTR a[rip]
        vmovaps xmm2, xmm1
        vandps  xmm2, xmm2, XMMWORD PTR .LC1[rip]
        vandps  xmm0, xmm0, XMMWORD PTR .LC0[rip]
        vorps   xmm0, xmm0, xmm2
        vmovss  DWORD PTR place[rip], xmm0
        ret