Use SmallVector to allocate Compound operands inline. (#20762)
Summary:
Reduces load time for serialized ResNet-18 by 5.5%.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20762
Differential Revision: D15437364
fbshipit-source-id: 2ba34dd229a1054553d0ee09f044ce1915377d78
