[Auto Parallel] do not fold global to sub reshard (#70023)

Author: deepllz

python/paddle/distributed/auto_parallel/static/pir_pass.py

@@ -63,11 +63,19 @@ def reshard_single_value(program, op, operand, attr):
             # fold reshard
             if prev_var.get_defining_op().name() == 'dist_op.reshard':
                 prev_reshard = prev_var.get_defining_op()
-                prev_var = prev_reshard.operand_source(0)
-                if prev_var.dist_attr() == operand_attr:
-                    return prev_var
-                reshard_var = paddle._C_ops.reshard_v2(prev_var, operand_attr)
-                return reshard_var
+                prev_reshard_input = prev_reshard.operand_source(0)
+                prev_reshard_result = prev_reshard.result(0)
+                # skil global to sub mesh reshard
+                if (
+                    prev_reshard_input.dist_attr().process_mesh.ndim
+                    == prev_reshard_result.dist_attr().process_mesh.ndim
+                ):
+                    if prev_reshard_input.dist_attr() == operand_attr:
+                        return prev_reshard_input
+                    reshard_var = paddle._C_ops.reshard_v2(
+                        prev_reshard_input, operand_attr
+                    )
+                    return reshard_var
             # insert reshard
             reshard_var = paddle._C_ops.reshard_v2(prev_var, operand_attr)
             return reshard_var