Port 2332ebd8
https://crrev.com/c/2264099

Original Commit Message:

  - Add a separate function to load return slots, instead of encoding this
  in the offset,
  - Add fast path for single return.

Change-Id: I065c35b95dbc6546387ea54d298bb5765bc342cd
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2269456Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Zhao Jiazhong <zhaojiazhong-hf@loongson.cn>
Cr-Commit-Position: refs/heads/master@{#68569}