[BUG] unexpected add behavier. about taichi HOT 3 OPEN

import taichi as ti
ti.init(ti.cuda)

@ti.kernel
def mytest():
    for _ in range(1):
        x = ti.Vector.zero(ti.f32, 1)
        x[0] = 1
        res = ti.Vector.zero(ti.f32, 1)
        for i in range(1):
            res[i] = 2
        x = res
        print(x)
        print(x[0])

mytest()

import taichi as ti
import numpy as np

ti.init(arch=ti.gpu)
num = int(1e9)
@ti.kernel
def speed_test()->ti.float32:
   ti.loop_config(serialize=True)
   s2 = 0.0
   for i in range(num):
      s2+=1.0
   return s2
print(speed_test())
a = np.ones(num,dtype=np.float32)
res = np.array(0.0,dtype=np.float32)
a.sum(out=res)
print(res)