Add simplify pass in the Relay interpreter (#2417)

python/tvm/relay/backend/interpreter.py

@@ -218,7 +218,9 @@ class Interpreter(Executor):
         """
         # TODO: We need to move this optimization code into the optimizer/pass manager
         ck_expr = ir_pass.infer_type(expr, mod=self.mod)
-        fused_expr = ir_pass.fuse_ops(ck_expr)
+        simp_expr = ir_pass.simplify_inference(ck_expr)
+        ck_simp = ir_pass.infer_type(simp_expr, mod=self.mod)
+        fused_expr = ir_pass.fuse_ops(ck_simp)
         ck_fused = ir_pass.infer_type(fused_expr, mod=self.mod)
         return ck_fused