[Lang] [bug] Make comparisons always return i32 (#5487)

* [Lang] [bug] Make comparisons independent of default_ip

* Fix tests

python/taichi/lang/ast/ast_transformer.py

@@ -784,6 +784,8 @@ def build_Compare(ctx, node):
                         f'"{type(node_op).__name__}" is not supported in Taichi kernels.'
                     )
             val = ti_ops.bit_and(val, op(l, r))
+        if not isinstance(val, bool):
+            val = ti_ops.cast(val, primitive_types.i32)
         node.ptr = val
         return node.ptr
 

tests/python/test_compare.py

@@ -198,3 +198,17 @@ def is_f32(tp: ti.template()) -> ti.i32:
             return tp is ti.f32
 
         is_f32(ti.f32)
+
+
+@test_utils.test(default_ip=ti.i64, require=ti.extension.data64)
+def test_compare_ret_type():
+    # The purpose of this test is to make sure a comparison returns i32
+    # regardless of default_ip so that it can always serve as the condition of
+    # an if statement.
+    @ti.kernel
+    def foo():
+        for i in range(100):
+            if i == 0:
+                pass
+
+    foo()