Comment by xoranth

On x86-64, compilers use SIMD instructions and registers to implement floating point math, they just use the single lane instructions. E.g. (https://godbolt.org/z/94b3r8dMn):

    float my_func(float lhs, float rhs) {
        return 2.0f * lhs - 3.0f * rhs;
    }

Becomes:

    my_func(float, float):
        addss   xmm0, xmm0
        mulss   xmm1, DWORD PTR .LC0[rip]
        subss   xmm0, xmm1
        ret

(addss, mulss and subss are SSE2 instructions.)