Auto merge of #48411 - nikomatsakis:chalkify-canonical-query-mir, r=<try>

introduce canonical queries, use for normalization and dropck-outlives

This branch adds in the concept of a **canonicalized trait query** and uses it for three specific operations:

- `infcx.at(cause, param_env).normalize(type_foldable)`
    - normalizes all associated types in `type_foldable`
- `tcx.normalize_erasing_regions(param_env, type_foldable)`
    - like normalize, but erases regions first and in the result; this leads to better caching
- `infcx.at(cause, param_env).dropck_outlives(ty)`
    - produces the set of types that must be live when a value of type `ty` is dropped
    - used from dropck but also NLL outlives

This is a kind of "first step" towards a more Chalk-ified approach. It leads to a **big** speedup for NLL, which is basically dominated by the dropck-outlives computation. Here are some timing measurements for the `syn` crate (pre-branch measurements coming soon):

| Commit | NLL disabled | NLL enabled |
| ------- | --- | --- |
| Before my branch | 5.43s | 8.99s |
| After my branch | 5.36s | 7.25s |

(Note that NLL enabled still does *all the work* that NLL disabled does, so this is not really a way to compare the performance of NLL versus the AST-based borrow checker directly.) Since this affects all codepaths, I'd like to do a full perf run before we land anything.

Also, this is not the "final point" for canonicalization etc. I think canonicalization can be made substantially faster, for one thing. But it seems like a reasonable starting point for a branch that's gotten a bit larger than I would have liked.

**Commit convention:** First of all, this entire branch ought to be a "pure refactoring", I believe, not changing anything about external behavior. Second, I've tagged the most important commits with `[VIC]` (very important commit), so you can scan for those. =)

r? @eddyb

Author: bors

src/Cargo.lock

@@ -60,18 +60,17 @@
 //! user of the `DepNode` API of having to know how to compute the expected
 //! fingerprint for a given set of node parameters.
 
+use ich::{Fingerprint, StableHashingContext};
+use infer::canonical::Canonical;
 use hir::def_id::{CrateNum, DefId, DefIndex, CRATE_DEF_INDEX};
 use hir::map::DefPathHash;
 use hir::{HirId, ItemLocalId};
-
-use ich::Fingerprint;
-use ty::{TyCtxt, Instance, InstanceDef, ParamEnv, ParamEnvAnd, PolyTraitRef, Ty};
-use ty::subst::Substs;
 use rustc_data_structures::stable_hasher::{StableHasher, HashStable};
-use ich::StableHashingContext;
 use std::fmt;
 use std::hash::Hash;
 use syntax_pos::symbol::InternedString;
+use ty::{self, TyCtxt, Instance, InstanceDef, ParamEnv, ParamEnvAnd, PolyTraitRef, Ty};
+use ty::subst::Substs;
 
 // erase!() just makes tokens go away. It's used to specify which macro argument
 // is repeated (i.e. which sub-expression of the macro we are in) but don't need
@@ -630,6 +629,8 @@ define_dep_nodes!( <'tcx>
     [] CompileCodegenUnit(InternedString),
     [input] OutputFilenames,
     [anon] NormalizeTy,
+    [] NormalizeProjectionTy { ty: &'tcx Canonical<ParamEnvAnd<'tcx, ty::ProjectionTy<'tcx>>> },
+
     // We use this for most things when incr. comp. is turned off.
     [] Null,
 

src/librustc/dep_graph/dep_node.rs

@@ -19,6 +19,7 @@ use std::cell::RefCell;
 use std::hash as std_hash;
 use std::mem;
 use middle::region;
+use infer::{self, canonical};
 use traits;
 use ty;
 
@@ -73,6 +74,9 @@ for ty::RegionKind {
             ty::ReEmpty => {
                 // No variant fields to hash for these ...
             }
+            ty::ReCanonical(c) => {
+                c.hash_stable(hcx, hasher);
+            }
             ty::ReLateBound(db, ty::BrAnon(i)) => {
                 db.depth.hash_stable(hcx, hasher);
                 i.hash_stable(hcx, hasher);
@@ -118,6 +122,16 @@ impl<'gcx> HashStable<StableHashingContext<'gcx>> for ty::RegionVid {
     }
 }
 
+impl<'gcx> HashStable<StableHashingContext<'gcx>> for ty::CanonicalVar {
+    #[inline]
+    fn hash_stable<W: StableHasherResult>(&self,
+                                          hcx: &mut StableHashingContext<'gcx>,
+                                          hasher: &mut StableHasher<W>) {
+        use rustc_data_structures::indexed_vec::Idx;
+        self.index().hash_stable(hcx, hasher);
+    }
+}
+
 impl<'gcx> HashStable<StableHashingContext<'gcx>>
 for ty::adjustment::AutoBorrow<'gcx> {
     fn hash_stable<W: StableHasherResult>(&self,
@@ -804,12 +818,6 @@ impl_stable_hash_for!(struct ty::Destructor {
     did
 });
 
-impl_stable_hash_for!(struct ty::DtorckConstraint<'tcx> {
-    outlives,
-    dtorck_types
-});
-
-
 impl<'gcx> HashStable<StableHashingContext<'gcx>> for ty::CrateVariancesMap {
     fn hash_stable<W: StableHasherResult>(&self,
                                           hcx: &mut StableHashingContext<'gcx>,
@@ -1028,3 +1036,58 @@ for traits::VtableGeneratorData<'gcx, N> where N: HashStable<StableHashingContex
         nested.hash_stable(hcx, hasher);
     }
 }
+
+impl<'gcx, V> HashStable<StableHashingContext<'gcx>>
+for canonical::Canonical<V> where V: HashStable<StableHashingContext<'gcx>> {
+    fn hash_stable<W: StableHasherResult>(&self,
+                                          hcx: &mut StableHashingContext<'gcx>,
+                                          hasher: &mut StableHasher<W>) {
+        let canonical::Canonical {
+            variables,
+            value,
+        } = self;
+        variables.hash_stable(hcx, hasher);
+        value.hash_stable(hcx, hasher);
+    }
+}
+
+impl<'gcx> HashStable<StableHashingContext<'gcx>>
+for canonical::CanonicalVarValues<'gcx> {
+    fn hash_stable<W: StableHasherResult>(&self,
+                                          hcx: &mut StableHashingContext<'gcx>,
+                                          hasher: &mut StableHasher<W>) {
+        let canonical::CanonicalVarValues {
+            var_values,
+        } = self;
+        var_values.hash_stable(hcx, hasher);
+    }
+}
+
+impl_stable_hash_for!(struct infer::canonical::CanonicalVarInfo {
+    kind
+});
+
+impl_stable_hash_for!(enum infer::canonical::CanonicalVarKind {
+    Ty(k),
+    Region
+});
+
+impl_stable_hash_for!(enum infer::canonical::CanonicalTyVarKind {
+    General,
+    Int,
+    Float
+});
+
+impl_stable_hash_for!(
+    impl<'tcx, R> for struct infer::canonical::QueryResult<'tcx, R> {
+        var_values, region_constraints, certainty, value
+    }
+);
+
+impl_stable_hash_for!(struct infer::canonical::QueryRegionConstraints<'tcx> {
+    region_outlives, ty_outlives
+});
+
+impl_stable_hash_for!(enum infer::canonical::Certainty {
+    Proven, Ambiguous
+});

src/librustc/ich/impls_ty.rs

@@ -40,9 +40,9 @@ use super::*;
 use ty::relate::{Relate, TypeRelation};
 
 pub struct At<'a, 'gcx: 'tcx, 'tcx: 'a> {
-    infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
-    cause: &'a ObligationCause<'tcx>,
-    param_env: ty::ParamEnv<'tcx>,
+    pub infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
+    pub cause: &'a ObligationCause<'tcx>,
+    pub param_env: ty::ParamEnv<'tcx>,
 }
 
 pub struct Trace<'a, 'gcx: 'tcx, 'tcx: 'a> {
@@ -281,6 +281,20 @@ impl<'tcx> ToTrace<'tcx> for Ty<'tcx> {
     }
 }
 
+impl<'tcx> ToTrace<'tcx> for ty::Region<'tcx> {
+    fn to_trace(cause: &ObligationCause<'tcx>,
+                a_is_expected: bool,
+                a: Self,
+                b: Self)
+                -> TypeTrace<'tcx>
+    {
+        TypeTrace {
+            cause: cause.clone(),
+            values: Regions(ExpectedFound::new(a_is_expected, a, b))
+        }
+    }
+}
+
 impl<'tcx> ToTrace<'tcx> for ty::TraitRef<'tcx> {
     fn to_trace(cause: &ObligationCause<'tcx>,
                 a_is_expected: bool,