Auto merge of #51570 - oli-obk:demotion, r=<try>

Do not promote constants that contain unpromotable code

r? @eddyb

cc @nikomatsakis

I'll add more tests, just getting this out for a crater run

Author: bors

src/librustc/hir/map/blocks.rs

@@ -52,6 +52,12 @@ impl MaybeFnLike for ast::Item {
     }
 }
 
+impl MaybeFnLike for ast::ImplItem {
+    fn is_fn_like(&self) -> bool {
+        match self.node { ast::ImplItemKind::Method(..) => true, _ => false, }
+    }
+}
+
 impl MaybeFnLike for ast::TraitItem {
     fn is_fn_like(&self) -> bool {
         match self.node {
@@ -144,7 +150,7 @@ impl<'a> FnLikeNode<'a> {
         let fn_like = match node {
             map::NodeItem(item) => item.is_fn_like(),
             map::NodeTraitItem(tm) => tm.is_fn_like(),
-            map::NodeImplItem(_) => true,
+            map::NodeImplItem(it) => it.is_fn_like(),
             map::NodeExpr(e) => e.is_fn_like(),
             _ => false
         };

src/librustc/ty/steal.rs

@@ -49,6 +49,11 @@ impl<T> Steal<T> {
         })
     }
 
+    /// In case of cyclic queries, use this function to break the cycle
+    pub fn try_borrow(&self) -> ReadGuard<Option<T>> {
+        self.value.borrow()
+    }
+
     pub fn steal(&self) -> T {
         let value_ref = &mut *self.value.try_write().expect("stealing value which is locked");
         let value = mem::replace(value_ref, None);

src/librustc_metadata/decoder.rs

@@ -415,9 +415,9 @@ impl<'tcx> EntryKind<'tcx> {
             EntryKind::ForeignMutStatic => Def::Static(did, true),
             EntryKind::Struct(_, _) => Def::Struct(did),
             EntryKind::Union(_, _) => Def::Union(did),
-            EntryKind::Fn(_) |
+            EntryKind::Fn(..) |
             EntryKind::ForeignFn(_) => Def::Fn(did),
-            EntryKind::Method(_) => Def::Method(did),
+            EntryKind::Method(..) => Def::Method(did),
             EntryKind::Type => Def::TyAlias(did),
             EntryKind::AssociatedType(_) => Def::AssociatedTy(did),
             EntryKind::Mod(_) => Def::Mod(did),
@@ -765,7 +765,13 @@ impl<'a, 'tcx> CrateMetadata {
         match self.entry(id).kind {
             EntryKind::AssociatedConst(_, data, _) |
             EntryKind::Const(data, _) => data.ast_promotable,
-            _ => bug!(),
+            EntryKind::Fn(ref data) => {
+                data.decode(self).qualif.map_or(false, |q| q.ast_promotable)
+            },
+            EntryKind::Method(ref data) => {
+                data.decode(self).fn_data.qualif.map_or(false, |q| q.ast_promotable)
+            },
+            _ => bug!("{:?}", id),
         }
     }
 
@@ -791,6 +797,8 @@ impl<'a, 'tcx> CrateMetadata {
             EntryKind::AssociatedConst(AssociatedContainer::ImplFinal, qualif, _) => {
                 qualif.mir
             }
+            EntryKind::Method(data) => data.decode(self).fn_data.qualif.map_or(0, |q| q.mir),
+            EntryKind::Fn(data) => data.decode(self).qualif.map_or(0, |q| q.mir),
             _ => bug!(),
         }
     }

src/librustc_metadata/encoder.rs

@@ -827,6 +827,7 @@ impl<'a, 'b: 'a, 'tcx: 'b> IsolatedEncoder<'a, 'b, 'tcx> {
                         constness: hir::Constness::NotConst,
                         arg_names,
                         sig: self.lazy(&tcx.fn_sig(def_id)),
+                        qualif: None,
                     }
                 } else {
                     bug!()
@@ -880,6 +881,20 @@ impl<'a, 'b: 'a, 'tcx: 'b> IsolatedEncoder<'a, 'b, 'tcx> {
         !self.tcx.sess.opts.output_types.should_codegen()
     }
 
+    fn const_fn_qualif(
+        &self,
+        def_id: DefId,
+        body_id: hir::BodyId,
+        span: Span,
+    ) -> Option<ConstQualif> {
+        if self.tcx.is_const_fn(def_id) {
+            let mir = self.tcx.at(span).mir_const_qualif(def_id).0;
+            Some(self.const_qualif(mir, body_id))
+        } else {
+            None
+        }
+    }
+
     fn const_qualif(&self, mir: u8, body_id: hir::BodyId) -> ConstQualif {
         let body_owner_def_id = self.tcx.hir.body_owner_def_id(body_id);
         let ast_promotable = self.tcx.const_is_rvalue_promotable_to_static(body_owner_def_id);
@@ -915,11 +930,12 @@ impl<'a, 'b: 'a, 'tcx: 'b> IsolatedEncoder<'a, 'b, 'tcx> {
                 }
             }
             ty::AssociatedKind::Method => {
-                let fn_data = if let hir::ImplItemKind::Method(ref sig, body) = ast_item.node {
+                let fn_data = if let hir::ImplItemKind::Method(ref sig, body_id) = ast_item.node {
                     FnData {
                         constness: sig.constness,
-                        arg_names: self.encode_fn_arg_names_for_body(body),
+                        arg_names: self.encode_fn_arg_names_for_body(body_id),
                         sig: self.lazy(&tcx.fn_sig(def_id)),
+                        qualif: self.const_fn_qualif(def_id, body_id, ast_item.span),
                     }
                 } else {
                     bug!()
@@ -1045,13 +1061,13 @@ impl<'a, 'b: 'a, 'tcx: 'b> IsolatedEncoder<'a, 'b, 'tcx> {
                     self.encode_rendered_const_for_body(body_id)
                 )
             }
-            hir::ItemFn(_, _, constness, .., body) => {
+            hir::ItemFn(_, _, constness, .., body_id) => {
                 let data = FnData {
                     constness,
-                    arg_names: self.encode_fn_arg_names_for_body(body),
+                    arg_names: self.encode_fn_arg_names_for_body(body_id),
                     sig: self.lazy(&tcx.fn_sig(def_id)),
+                    qualif: self.const_fn_qualif(def_id, body_id, item.span),
                 };
-
                 EntryKind::Fn(self.lazy(&data))
             }
             hir::ItemMod(ref m) => {
@@ -1565,6 +1581,7 @@ impl<'a, 'b: 'a, 'tcx: 'b> IsolatedEncoder<'a, 'b, 'tcx> {
                     constness: hir::Constness::NotConst,
                     arg_names: self.encode_fn_arg_names(names),
                     sig: self.lazy(&tcx.fn_sig(def_id)),
+                    qualif: None,
                 };
                 EntryKind::ForeignFn(self.lazy(&data))
             }

src/librustc_metadata/schema.rs

@@ -434,9 +434,10 @@ pub struct FnData<'tcx> {
     pub constness: hir::Constness,
     pub arg_names: LazySeq<ast::Name>,
     pub sig: Lazy<ty::PolyFnSig<'tcx>>,
+    pub qualif: Option<ConstQualif>,
 }
 
-impl_stable_hash_for!(struct FnData<'tcx> { constness, arg_names, sig });
+impl_stable_hash_for!(struct FnData<'tcx> { constness, arg_names, sig, qualif });
 
 #[derive(RustcEncodable, RustcDecodable)]
 pub struct VariantData<'tcx> {

src/librustc_mir/build/mod.rs

@@ -35,7 +35,7 @@ use util as mir_util;
 
 /// Construct the MIR for a given def-id.
 pub fn mir_build<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> Mir<'tcx> {
-    let id = tcx.hir.as_local_node_id(def_id).unwrap();
+    let id = tcx.hir.as_local_node_id(def_id).expect("can't build non-local MIR");
     let unsupported = || {
         span_bug!(tcx.hir.span(id), "can't build MIR for {:?}", def_id);
     };

src/librustc_mir/transform/mod.rs

@@ -210,6 +210,10 @@ fn mir_validated<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> &'tcx
         // Ensure that we compute the `mir_const_qualif` for constants at
         // this point, before we steal the mir-const result.
         let _ = tcx.mir_const_qualif(def_id);
+    } else if tcx.is_const_fn(def_id) {
+        // Ensure that we compute the `mir_const_qualif` for const fns at
+        // this point, before we steal the mir-const result.
+        let _ = tcx.mir_const_qualif(def_id);
     }
 
     let mut mir = tcx.mir_const(def_id).steal();