rustc: use monomorphic const_eval for cross-crate enum discriminants.

Author: eddyb

src/librustc/ty/mod.rs

@@ -1660,7 +1660,7 @@ impl<'a, 'gcx, 'tcx> AdtDef {
         self.variants.iter().map(move |v| {
             let mut discr = prev_discr.map_or(initial, |d| d.wrap_incr());
             if let VariantDiscr::Explicit(expr_did) = v.discr {
-                match tcx.maps.monomorphic_const_eval.borrow()[&expr_did] {
+                match queries::monomorphic_const_eval::get(tcx, DUMMY_SP, expr_did) {
                     Ok(ConstVal::Integral(v)) => {
                         discr = v;
                     }
@@ -1673,6 +1673,51 @@ impl<'a, 'gcx, 'tcx> AdtDef {
         })
     }
 
+    /// Compute the discriminant value used by a specific variant.
+    /// Unlike `discriminants`, this is (amortized) constant-time,
+    /// only doing at most one query for evaluating an explicit
+    /// discriminant (the last one before the requested variant),
+    /// assuming there are no constant-evaluation errors there.
+    pub fn discriminant_for_variant(&self,
+                                    tcx: TyCtxt<'a, 'gcx, 'tcx>,
+                                    variant_index: usize)
+                                    -> ConstInt {
+        let repr_type = self.repr.discr_type();
+        let mut explicit_value = repr_type.initial_discriminant(tcx.global_tcx());
+        let mut explicit_index = variant_index;
+        loop {
+            match self.variants[explicit_index].discr {
+                ty::VariantDiscr::Relative(0) => break,
+                ty::VariantDiscr::Relative(distance) => {
+                    explicit_index -= distance;
+                }
+                ty::VariantDiscr::Explicit(expr_did) => {
+                    match queries::monomorphic_const_eval::get(tcx, DUMMY_SP, expr_did) {
+                        Ok(ConstVal::Integral(v)) => {
+                            explicit_value = v;
+                            break;
+                        }
+                        _ => {
+                            explicit_index -= 1;
+                        }
+                    }
+                }
+            }
+        }
+        let discr = explicit_value.to_u128_unchecked()
+            .wrapping_add((variant_index - explicit_index) as u128);
+        match repr_type {
+            attr::UnsignedInt(ty) => {
+                ConstInt::new_unsigned_truncating(discr, ty,
+                                                  tcx.sess.target.uint_type)
+            }
+            attr::SignedInt(ty) => {
+                ConstInt::new_signed_truncating(discr as i128, ty,
+                                                tcx.sess.target.int_type)
+            }
+        }
+    }
+
     pub fn destructor(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Option<Destructor> {
         queries::adt_destructor::get(tcx, DUMMY_SP, self.did)
     }

src/librustc_const_eval/eval.rs

@@ -804,10 +804,13 @@ pub fn provide(providers: &mut Providers) {
 fn monomorphic_const_eval<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                     def_id: DefId)
                                     -> EvalResult<'tcx> {
-    ty::queries::mir_const_qualif::get(tcx, DUMMY_SP, def_id);
     let cx = ConstContext::with_tables(tcx, tcx.item_tables(def_id));
 
-    let id = tcx.hir.as_local_node_id(def_id).unwrap();
-    let body = tcx.hir.body_owned_by(id);
-    cx.eval(&tcx.hir.body(body).value)
+    let body = if let Some(id) = tcx.hir.as_local_node_id(def_id) {
+        ty::queries::mir_const_qualif::get(tcx, DUMMY_SP, def_id);
+        tcx.hir.body(tcx.hir.body_owned_by(id))
+    } else {
+        tcx.sess.cstore.maybe_get_item_body(tcx, def_id).unwrap()
+    };
+    cx.eval(&body.value)
 }

src/librustc_driver/driver.rs

@@ -900,6 +900,8 @@ pub fn phase_3_run_analysis_passes<'tcx, F, R>(sess: &'tcx Session,
     let mut extern_providers = ty::maps::Providers::default();
     cstore::provide(&mut extern_providers);
     ty::provide_extern(&mut extern_providers);
+    // FIXME(eddyb) get rid of this once we replace const_eval with miri.
+    rustc_const_eval::provide(&mut extern_providers);
 
     TyCtxt::create_and_enter(sess,
                              local_providers,

src/librustc_incremental/persist/dirty_clean.rs

@@ -266,6 +266,17 @@ impl<'a, 'tcx, 'm> intravisit::Visitor<'tcx> for DirtyCleanMetadataVisitor<'a, '
         intravisit::walk_item(self, item);
     }
 
+    fn visit_variant(&mut self,
+                     variant: &'tcx hir::Variant,
+                     generics: &'tcx hir::Generics,
+                     parent_id: ast::NodeId) {
+        if let Some(e) = variant.node.disr_expr {
+            self.check_item(e.node_id, variant.span);
+        }
+
+        intravisit::walk_variant(self, variant, generics, parent_id);
+    }
+
     fn visit_variant_data(&mut self,
                           variant_data: &'tcx hir::VariantData,
                           _: ast::Name,

src/librustc_metadata/decoder.rs

@@ -511,25 +511,15 @@ impl<'a, 'tcx> CrateMetadata {
         def
     }
 
-    fn get_variant(&self,
-                   item: &Entry<'tcx>,
-                   index: DefIndex,
-                   tcx: TyCtxt<'a, 'tcx, 'tcx>)
-                   -> (ty::VariantDef, Option<DefIndex>) {
+    fn get_variant(&self, item: &Entry, index: DefIndex) -> ty::VariantDef {
         let data = match item.kind {
             EntryKind::Variant(data) |
             EntryKind::Struct(data, _) |
             EntryKind::Union(data, _) => data.decode(self),
             _ => bug!(),
         };
 
-        if let ty::VariantDiscr::Explicit(def_id) = data.discr {
-            // The original crate wouldn't have compiled if this is missing.
-            let result = Ok(data.evaluated_discr.unwrap());
-            tcx.maps.monomorphic_const_eval.borrow_mut().insert(def_id, result);
-        }
-
-        (ty::VariantDef {
+        ty::VariantDef {
             did: self.local_def_id(data.struct_ctor.unwrap_or(index)),
             name: self.item_name(index),
             fields: item.children.decode(self).map(|index| {
@@ -542,7 +532,7 @@ impl<'a, 'tcx> CrateMetadata {
             }).collect(),
             discr: data.discr,
             ctor_kind: data.ctor_kind,
-        }, data.struct_ctor)
+        }
     }
 
     pub fn get_adt_def(&self,
@@ -561,15 +551,11 @@ impl<'a, 'tcx> CrateMetadata {
             item.children
                 .decode(self)
                 .map(|index| {
-                    let (variant, struct_ctor) =
-                        self.get_variant(&self.entry(index), index, tcx);
-                    assert_eq!(struct_ctor, None);
-                    variant
+                    self.get_variant(&self.entry(index), index)
                 })
                 .collect()
         } else {
-            let (variant, _struct_ctor) = self.get_variant(&item, item_id, tcx);
-            vec![variant]
+            vec![self.get_variant(&item, item_id)]
         };
         let (kind, repr) = match item.kind {
             EntryKind::Enum(repr) => (ty::AdtKind::Enum, repr),

src/librustc_metadata/encoder.rs

@@ -269,12 +269,6 @@ impl<'a, 'b: 'a, 'tcx: 'b> EntryBuilder<'a, 'b, 'tcx> {
         let data = VariantData {
             ctor_kind: variant.ctor_kind,
             discr: variant.discr,
-            evaluated_discr: match variant.discr {
-                ty::VariantDiscr::Explicit(def_id) => {
-                    ty::queries::monomorphic_const_eval::get(tcx, DUMMY_SP, def_id).ok()
-                }
-                ty::VariantDiscr::Relative(_) => None
-            },
             struct_ctor: None,
         };
 
@@ -408,7 +402,6 @@ impl<'a, 'b: 'a, 'tcx: 'b> EntryBuilder<'a, 'b, 'tcx> {
         let data = VariantData {
             ctor_kind: variant.ctor_kind,
             discr: variant.discr,
-            evaluated_discr: None,
             struct_ctor: Some(def_id.index),
         };
 
@@ -697,7 +690,6 @@ impl<'a, 'b: 'a, 'tcx: 'b> EntryBuilder<'a, 'b, 'tcx> {
                 EntryKind::Struct(self.lazy(&VariantData {
                     ctor_kind: variant.ctor_kind,
                     discr: variant.discr,
-                    evaluated_discr: None,
                     struct_ctor: struct_ctor,
                 }), repr_options)
             }
@@ -708,7 +700,6 @@ impl<'a, 'b: 'a, 'tcx: 'b> EntryBuilder<'a, 'b, 'tcx> {
                 EntryKind::Union(self.lazy(&VariantData {
                     ctor_kind: variant.ctor_kind,
                     discr: variant.discr,
-                    evaluated_discr: None,
                     struct_ctor: None,
                 }), repr_options)
             }
@@ -1037,6 +1028,17 @@ impl<'a, 'b, 'tcx> Visitor<'tcx> for EncodeVisitor<'a, 'b, 'tcx> {
                           EntryBuilder::encode_info_for_foreign_item,
                           (def_id, ni));
     }
+    fn visit_variant(&mut self,
+                     v: &'tcx hir::Variant,
+                     g: &'tcx hir::Generics,
+                     id: ast::NodeId) {
+        intravisit::walk_variant(self, v, g, id);
+
+        if let Some(discr) = v.node.disr_expr {
+            let def_id = self.index.tcx.hir.body_owner_def_id(discr);
+            self.index.record(def_id, EntryBuilder::encode_info_for_embedded_const, def_id);
+        }
+    }
     fn visit_generics(&mut self, generics: &'tcx hir::Generics) {
         intravisit::walk_generics(self, generics);
         self.index.encode_info_for_generics(generics);
@@ -1160,6 +1162,32 @@ impl<'a, 'b: 'a, 'tcx: 'b> EntryBuilder<'a, 'b, 'tcx> {
         }
     }
 
+    fn encode_info_for_embedded_const(&mut self, def_id: DefId) -> Entry<'tcx> {
+        debug!("EntryBuilder::encode_info_for_embedded_const({:?})", def_id);
+        let tcx = self.tcx;
+        let id = tcx.hir.as_local_node_id(def_id).unwrap();
+        let body = tcx.hir.body_owned_by(id);
+
+        Entry {
+            kind: EntryKind::Const(ty::queries::mir_const_qualif::get(tcx, DUMMY_SP, def_id)),
+            visibility: self.lazy(&ty::Visibility::Public),
+            span: self.lazy(&tcx.def_span(def_id)),
+            attributes: LazySeq::empty(),
+            children: LazySeq::empty(),
+            stability: None,
+            deprecation: None,
+
+            ty: Some(self.encode_item_type(def_id)),
+            inherent_impls: LazySeq::empty(),
+            variances: LazySeq::empty(),
+            generics: Some(self.encode_generics(def_id)),
+            predicates: Some(self.encode_predicates(def_id)),
+
+            ast: Some(self.encode_body(body)),
+            mir: self.encode_mir(def_id),
+        }
+    }
+
     fn encode_attributes(&mut self, attrs: &[ast::Attribute]) -> LazySeq<ast::Attribute> {
         // NOTE: This must use lazy_seq_from_slice(), not lazy_seq() because
         //       we really on the HashStable specialization for [Attribute]

src/librustc_metadata/schema.rs

@@ -15,7 +15,6 @@ use rustc::hir;
 use rustc::hir::def::{self, CtorKind};
 use rustc::hir::def_id::{DefIndex, DefId};
 use rustc::ich::StableHashingContext;
-use rustc::middle::const_val::ConstVal;
 use rustc::middle::cstore::{DepKind, LinkagePreference, NativeLibrary};
 use rustc::middle::lang_items;
 use rustc::mir;
@@ -271,9 +270,9 @@ pub enum EntryKind<'tcx> {
     Type,
     Enum(ReprOptions),
     Field,
-    Variant(Lazy<VariantData<'tcx>>),
-    Struct(Lazy<VariantData<'tcx>>, ReprOptions),
-    Union(Lazy<VariantData<'tcx>>, ReprOptions),
+    Variant(Lazy<VariantData>),
+    Struct(Lazy<VariantData>, ReprOptions),
+    Union(Lazy<VariantData>, ReprOptions),
     Fn(Lazy<FnData>),
     ForeignFn(Lazy<FnData>),
     Mod(Lazy<ModData>),
@@ -374,20 +373,18 @@ pub struct FnData {
 impl_stable_hash_for!(struct FnData { constness, arg_names });
 
 #[derive(RustcEncodable, RustcDecodable)]
-pub struct VariantData<'tcx> {
+pub struct VariantData {
     pub ctor_kind: CtorKind,
     pub discr: ty::VariantDiscr,
-    pub evaluated_discr: Option<ConstVal<'tcx>>,
 
     /// If this is a struct's only variant, this
     /// is the index of the "struct ctor" item.
     pub struct_ctor: Option<DefIndex>,
 }
 
-impl_stable_hash_for!(struct VariantData<'tcx> {
+impl_stable_hash_for!(struct VariantData {
     ctor_kind,
     discr,
-    evaluated_discr,
     struct_ctor
 });
 

src/librustc_trans/adt.rs

@@ -41,8 +41,6 @@
 //!   used unboxed and any field can have pointers (including mutable)
 //!   taken to it, implementing them for Rust seems difficult.
 
-use super::Disr;
-
 use std;
 
 use llvm::{ValueRef, True, IntEQ, IntNE};
@@ -347,31 +345,31 @@ fn load_discr(bcx: &Builder, ity: layout::Integer, ptr: ValueRef,
 
 /// Set the discriminant for a new value of the given case of the given
 /// representation.
-pub fn trans_set_discr<'a, 'tcx>(bcx: &Builder<'a, 'tcx>, t: Ty<'tcx>, val: ValueRef, to: Disr) {
+pub fn trans_set_discr<'a, 'tcx>(bcx: &Builder<'a, 'tcx>, t: Ty<'tcx>, val: ValueRef, to: u64) {
     let l = bcx.ccx.layout_of(t);
     match *l {
         layout::CEnum{ discr, min, max, .. } => {
-            assert_discr_in_range(Disr(min), Disr(max), to);
-            bcx.store(C_integral(Type::from_integer(bcx.ccx, discr), to.0, true),
+            assert_discr_in_range(min, max, to);
+            bcx.store(C_integral(Type::from_integer(bcx.ccx, discr), to, true),
                   val, None);
         }
         layout::General{ discr, .. } => {
-            bcx.store(C_integral(Type::from_integer(bcx.ccx, discr), to.0, true),
+            bcx.store(C_integral(Type::from_integer(bcx.ccx, discr), to, true),
                   bcx.struct_gep(val, 0), None);
         }
         layout::Univariant { .. }
         | layout::UntaggedUnion { .. }
         | layout::Vector { .. } => {
-            assert_eq!(to, Disr(0));
+            assert_eq!(to, 0);
         }
         layout::RawNullablePointer { nndiscr, .. } => {
-            if to.0 != nndiscr {
+            if to != nndiscr {
                 let llptrty = val_ty(val).element_type();
                 bcx.store(C_null(llptrty), val, None);
             }
         }
         layout::StructWrappedNullablePointer { nndiscr, ref discrfield, ref nonnull, .. } => {
-            if to.0 != nndiscr {
+            if to != nndiscr {
                 if target_sets_discr_via_memset(bcx) {
                     // Issue #34427: As workaround for LLVM bug on
                     // ARM, use memset of 0 on whole struct rather
@@ -397,7 +395,7 @@ fn target_sets_discr_via_memset<'a, 'tcx>(bcx: &Builder<'a, 'tcx>) -> bool {
     bcx.sess().target.target.arch == "arm" || bcx.sess().target.target.arch == "aarch64"
 }
 
-pub fn assert_discr_in_range(min: Disr, max: Disr, discr: Disr) {
+pub fn assert_discr_in_range<D: PartialOrd>(min: D, max: D, discr: D) {
     if min <= max {
         assert!(min <= discr && discr <= max)
     } else {
@@ -415,7 +413,7 @@ fn roundup(x: u64, a: u32) -> u64 { let a = a as u64; ((x + (a - 1)) / a) * a }
 /// (Not to be confused with `common::const_get_elt`, which operates on
 /// raw LLVM-level structs and arrays.)
 pub fn const_get_field<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>, t: Ty<'tcx>,
-                       val: ValueRef, _discr: Disr,
+                       val: ValueRef,
                        ix: usize) -> ValueRef {
     let l = ccx.layout_of(t);
     match *l {