Auto merge of #77229 - tmiasko:liveness, r=lcnr

Small improvements in liveness pass

* Remove redundant debug logging (`add_variable` already contains logging).
* Remove redundant fields for a number of live nodes and variables.
* Delay conversion from a symbol to a string until linting.
* Inline contents of specials struct.
* Remove unnecessary local variable exit_ln.
* Use newtype_index for Variable and LiveNode.
* Access live nodes directly through self.lnks[ln].

No functional changes intended (except those related to the logging).

Author: bors

Cargo.lock

@@ -3891,6 +3891,7 @@ dependencies = [
  "rustc_hir",
  "rustc_index",
  "rustc_middle",
+ "rustc_serialize",
  "rustc_session",
  "rustc_span",
  "rustc_target",

compiler/rustc_passes/Cargo.toml

@@ -15,5 +15,6 @@ rustc_index = { path = "../rustc_index" }
 rustc_session = { path = "../rustc_session" }
 rustc_target = { path = "../rustc_target" }
 rustc_ast = { path = "../rustc_ast" }
+rustc_serialize = { path = "../rustc_serialize" }
 rustc_span = { path = "../rustc_span" }
 rustc_trait_selection = { path = "../rustc_trait_selection" }

compiler/rustc_passes/src/lib.rs

@@ -5,6 +5,8 @@
 //! This API is completely unstable and subject to change.
 
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
+#![feature(const_fn)]
+#![feature(const_panic)]
 #![feature(in_band_lifetimes)]
 #![feature(nll)]
 #![feature(or_patterns)]