[StaticRuntime] Replace hashtable based workspace with vector<IValue> (#45892)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/45892
Previously we were using hashtable (`std::unordered_map` in OSS, `folly::F14FastMap` in fb) for workspace, a container for all the IValues in the graph. Hashtable based lookups can be expensive. This diff replaces the hashtable with `std::vector` and extra bookkeepings are introduced to keep track of the indices of graph inputs/outputs in `StaticRuntime` and op inputs/outputs in `ProcessedNode`.
Reviewed By: dzhulgakov
Differential Revision: D24098763
fbshipit-source-id: 337f835ee144985029b5fa2ab98f9bcc5e3606b6
