Auto merge of rust-lang#50874 - nikomatsakis:nll-reset-unification, r=estebank

use `reset_unifications` instead of creating new unification table

This eliminates a hot spot in NLL performance.

Author: bors

src/Cargo.lock

@@ -588,7 +588,7 @@ dependencies = [
 
 [[package]]
 name = "ena"
-version = "0.9.2"
+version = "0.9.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "log 0.4.1 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1750,7 +1750,7 @@ version = "128.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "cfg-if 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "ena 0.9.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "ena 0.9.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "parking_lot 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "parking_lot_core 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1957,7 +1957,7 @@ name = "rustc_data_structures"
 version = "0.0.0"
 dependencies = [
  "cfg-if 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "ena 0.9.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "ena 0.9.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "parking_lot 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "parking_lot_core 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2999,7 +2999,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum dtoa 0.4.2 (registry+https://github.com/rust-lang/crates.io-index)" = "09c3753c3db574d215cba4ea76018483895d7bff25a31b49ba45db21c48e50ab"
 "checksum either 1.5.0 (registry+https://github.com/rust-lang/crates.io-index)" = "3be565ca5c557d7f59e7cfcf1844f9e3033650c929c6566f511e8005f205c1d0"
 "checksum elasticlunr-rs 2.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "4511b63d69dd5d31e8e29aed2c132c413f87acea8035d0584801feaab9dd1f0f"
-"checksum ena 0.9.2 (registry+https://github.com/rust-lang/crates.io-index)" = "f8b449f3b18c89d2dbe40548d2ee4fa58ea0a08b761992da6ecb9788e4688834"
+"checksum ena 0.9.3 (registry+https://github.com/rust-lang/crates.io-index)" = "88dc8393b3c7352f94092497f6b52019643e493b6b890eb417cdb7c46117e621"
 "checksum endian-type 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)" = "c34f04666d835ff5d62e058c3995147c06f42fe86ff053337632bca83e42702d"
 "checksum enum_primitive 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "be4551092f4d519593039259a9ed8daedf0da12e5109c5280338073eaeb81180"
 "checksum env_logger 0.5.8 (registry+https://github.com/rust-lang/crates.io-index)" = "be27f8ea102a7182093a80d98f0b78623b580eda8791cbe8e2345fe6e57567a6"

src/librustc/infer/region_constraints/mod.rs

@@ -318,7 +318,7 @@ impl<'tcx> RegionConstraintCollector<'tcx> {
         // should think carefully about whether it needs to be cleared
         // or updated in some way.
         let RegionConstraintCollector {
-            var_infos,
+            var_infos: _,
             data,
             lubs,
             glbs,
@@ -338,10 +338,7 @@ impl<'tcx> RegionConstraintCollector<'tcx> {
         // un-unified" state. Note that when we unify `a` and `b`, we
         // also insert `a <= b` and a `b <= a` edges, so the
         // `RegionConstraintData` contains the relationship here.
-        *unification_table = ut::UnificationTable::new();
-        for vid in var_infos.indices() {
-            unification_table.new_key(unify_key::RegionVidKey { min_vid: vid });
-        }
+        unification_table.reset_unifications(|vid| unify_key::RegionVidKey { min_vid: vid });
 
         mem::replace(data, RegionConstraintData::default())
     }

src/librustc_data_structures/Cargo.toml

@@ -9,7 +9,7 @@ path = "lib.rs"
 crate-type = ["dylib"]
 
 [dependencies]
-ena = "0.9.1"
+ena = "0.9.3"
 log = "0.4"
 rustc_cratesio_shim = { path = "../librustc_cratesio_shim" }
 serialize = { path = "../libserialize" }