fix: according the meaning of __uni_sync()

Author: 0xzhang

tests/python/test_simt.py

@@ -68,7 +68,7 @@ def test_unique():
     b = ti.field(dtype=ti.u32, shape=32)
 
     @ti.kernel
-    def foo():
+    def check():
         ti.loop_config(block_dim=32)
         for i in range(32):
             a[i] = ti.simt.warp.unique(ti.u32(0xFFFFFFFF), b[i])
@@ -77,18 +77,26 @@ def foo():
         b[i] = 0
         a[i] = -1
 
-    foo()
+    check()
 
     for i in range(32):
-        assert a[i] == 0
+        assert a[i] == 1
 
-    b[np.random.randint(0, 32)] = 666
+    for i in range(32):
+        b[i] = i + 100
 
-    foo()
+    check()
 
     for i in range(32):
         assert a[i] == 1
 
+    b[np.random.randint(0, 32)] = 0
+
+    check()
+
+    for i in range(32):
+        assert a[i] == 0
+
 
 @test_utils.test(arch=ti.cuda)
 def test_ballot():