Auto merge of #51538 - nikomatsakis:nll-perf-examination, r=<try>

[WIP] Convert NLL ops to caches

This is a extension of <#51460>. It uses a lot more caching than we used to do. This caching is not yet as efficient as it could be, but I'm curious to see the current perf results.

Author: bors

src/Cargo.lock

@@ -1781,6 +1781,7 @@ dependencies = [
  "bitflags 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "byteorder 1.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "chalk-engine 0.6.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "either 1.5.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "flate2 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "fmt_macros 0.0.0",
  "graphviz 0.0.0",

src/librustc/Cargo.toml

@@ -11,6 +11,7 @@ crate-type = ["dylib"]
 [dependencies]
 arena = { path = "../libarena" }
 bitflags = "1.0"
+either = "1.5.0"
 fmt_macros = { path = "../libfmt_macros" }
 graphviz = { path = "../libgraphviz" }
 jobserver = "0.1"