he may not know how to read assembler:

the question is - yes, its optimized or even directly evaluated.

here is an example:

func main() {
    x := 10+rand.Intn(10)
    for i := 1; i <= int(math.Sqrt(float64(x))); i++ {
        fmt.Println(i)
    }
}

which produces these relevant bits and pieces:

        movl    $1, CX
        jmp     main_pc193
main_pc79:
        (....)
main_pc193:
        xorps   X0, X0  // x0 := 0
        cvtsq2SD        AX, X0 // x0 = float(int(ax))
        sqrtsd  X0, X0  // x0 = sqrt(x0)
        cvttsd2SQ       X0, DX
        cmpq    CX, DX
        jle     main_pc79

so, the answer is - sqrt is calculated every iteration, so you better assign that to a variable outside the loop!