Add a new normalization query just for mir constants

Author: oli-obk

compiler/rustc_infer/src/infer/resolve.rs

@@ -1,5 +1,6 @@
 use super::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use super::{FixupError, FixupResult, InferCtxt, Span};
+use rustc_middle::mir;
 use rustc_middle::ty::fold::{TypeFolder, TypeVisitor};
 use rustc_middle::ty::{self, Const, InferConst, Ty, TyCtxt, TypeFoldable};
 
@@ -46,6 +47,10 @@ impl<'a, 'tcx> TypeFolder<'tcx> for OpportunisticVarResolver<'a, 'tcx> {
             ct.super_fold_with(self)
         }
     }
+
+    fn fold_mir_const(&mut self, constant: mir::ConstantKind<'tcx>) -> mir::ConstantKind<'tcx> {
+        constant.super_fold_with(self)
+    }
 }
 
 /// The opportunistic region resolver opportunistically resolves regions

compiler/rustc_middle/src/mir/mod.rs

@@ -2410,7 +2410,8 @@ pub struct Constant<'tcx> {
     pub literal: ConstantKind<'tcx>,
 }
 
-#[derive(Clone, Copy, PartialEq, PartialOrd, TyEncodable, TyDecodable, Hash, HashStable, Debug)]
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, TyEncodable, TyDecodable, Hash, HashStable, Debug)]
+#[derive(Lift)]
 pub enum ConstantKind<'tcx> {
     /// This constant came from the type system
     Ty(&'tcx ty::Const<'tcx>),
@@ -2709,7 +2710,13 @@ impl<'tcx> Display for Constant<'tcx> {
             ty::FnDef(..) => {}
             _ => write!(fmt, "const ")?,
         }
-        match self.literal {
+        Display::fmt(&self.literal, fmt)
+    }
+}
+
+impl<'tcx> Display for ConstantKind<'tcx> {
+    fn fmt(&self, fmt: &mut Formatter<'_>) -> fmt::Result {
+        match *self {
             ConstantKind::Ty(c) => pretty_print_const(c, fmt, true),
             ConstantKind::Val(val, ty) => pretty_print_const_value(val, ty, fmt, true),
         }

compiler/rustc_middle/src/mir/type_foldable.rs

@@ -348,6 +348,10 @@ impl<'tcx> TypeFoldable<'tcx> for Constant<'tcx> {
 }
 
 impl<'tcx> TypeFoldable<'tcx> for ConstantKind<'tcx> {
+    fn fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Self {
+        folder.fold_mir_const(self)
+    }
+
     fn super_fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Self {
         match self {
             ConstantKind::Ty(c) => ConstantKind::Ty(c.fold_with(folder)),

compiler/rustc_middle/src/query/mod.rs

@@ -1482,6 +1482,13 @@ rustc_queries! {
         desc { "normalizing `{}`", goal.value }
     }
 
+    /// Do not call this query directly: invoke `normalize_erasing_regions` instead.
+    query normalize_mir_const_after_erasing_regions(
+        goal: ParamEnvAnd<'tcx, mir::ConstantKind<'tcx>>
+    ) -> mir::ConstantKind<'tcx> {
+        desc { "normalizing `{}`", goal.value }
+    }
+
     query implied_outlives_bounds(
         goal: CanonicalTyGoal<'tcx>
     ) -> Result<

compiler/rustc_middle/src/ty/erase_regions.rs

@@ -1,3 +1,4 @@
+use crate::mir;
 use crate::ty::fold::{TypeFoldable, TypeFolder};
 use crate::ty::{self, Ty, TyCtxt, TypeFlags};
 
@@ -65,4 +66,8 @@ impl TypeFolder<'tcx> for RegionEraserVisitor<'tcx> {
             _ => self.tcx.lifetimes.re_erased,
         }
     }
+
+    fn fold_mir_const(&mut self, c: mir::ConstantKind<'tcx>) -> mir::ConstantKind<'tcx> {
+        c.super_fold_with(self)
+    }
 }

compiler/rustc_middle/src/ty/fold.rs

@@ -30,6 +30,7 @@
 //!
 //! These methods return true to indicate that the visitor has found what it is
 //! looking for, and does not need to visit anything else.
+use crate::mir;
 use crate::ty::{self, flags::FlagComputation, Binder, Ty, TyCtxt, TypeFlags};
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
@@ -179,6 +180,10 @@ pub trait TypeFolder<'tcx>: Sized {
     fn fold_const(&mut self, c: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
         c.super_fold_with(self)
     }
+
+    fn fold_mir_const(&mut self, c: mir::ConstantKind<'tcx>) -> mir::ConstantKind<'tcx> {
+        bug!("most type folders should not be folding MIR datastructures: {:?}", c)
+    }
 }
 
 pub trait TypeVisitor<'tcx>: Sized {

compiler/rustc_middle/src/ty/normalize_erasing_regions.rs

@@ -7,6 +7,7 @@
 //! `normalize_generic_arg_after_erasing_regions` query for each type
 //! or constant found within. (This underlying query is what is cached.)
 
+use crate::mir;
 use crate::ty::fold::{TypeFoldable, TypeFolder};
 use crate::ty::subst::{Subst, SubstsRef};
 use crate::ty::{self, Ty, TyCtxt};
@@ -101,4 +102,9 @@ impl TypeFolder<'tcx> for NormalizeAfterErasingRegionsFolder<'tcx> {
         let arg = self.param_env.and(c.into());
         self.tcx.normalize_generic_arg_after_erasing_regions(arg).expect_const()
     }
+
+    fn fold_mir_const(&mut self, c: mir::ConstantKind<'tcx>) -> mir::ConstantKind<'tcx> {
+        let arg = self.param_env.and(c);
+        self.tcx.normalize_mir_const_after_erasing_regions(arg)
+    }
 }

compiler/rustc_middle/src/ty/subst.rs

@@ -1,5 +1,6 @@
 // Type substitutions.
 
+use crate::mir;
 use crate::ty::codec::{TyDecoder, TyEncoder};
 use crate::ty::fold::{TypeFoldable, TypeFolder, TypeVisitor};
 use crate::ty::sty::{ClosureSubsts, GeneratorSubsts};
@@ -503,6 +504,10 @@ impl<'a, 'tcx> TypeFolder<'tcx> for SubstFolder<'a, 'tcx> {
             c.super_fold_with(self)
         }
     }
+
+    fn fold_mir_const(&mut self, c: mir::ConstantKind<'tcx>) -> mir::ConstantKind<'tcx> {
+        c.super_fold_with(self)
+    }
 }
 
 impl<'a, 'tcx> SubstFolder<'a, 'tcx> {

compiler/rustc_mir/src/monomorphize/collector.rs

@@ -184,7 +184,6 @@ use rustc_hir::def_id::{DefId, DefIdMap, LocalDefId, LOCAL_CRATE};
 use rustc_hir::itemlikevisit::ItemLikeVisitor;
 use rustc_hir::lang_items::LangItem;
 use rustc_index::bit_set::GrowableBitSet;
-use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use rustc_middle::mir::interpret::{AllocId, ConstValue};
 use rustc_middle::mir::interpret::{ErrorHandled, GlobalAlloc, Scalar};
 use rustc_middle::mir::mono::{InstantiationMode, MonoItem};
@@ -193,6 +192,7 @@ use rustc_middle::mir::{self, Local, Location};
 use rustc_middle::ty::adjustment::{CustomCoerceUnsized, PointerCast};
 use rustc_middle::ty::subst::{GenericArgKind, InternalSubsts};
 use rustc_middle::ty::{self, GenericParamDefKind, Instance, Ty, TyCtxt, TypeFoldable};
+use rustc_middle::{middle::codegen_fn_attrs::CodegenFnAttrFlags, mir::visit::TyContext};
 use rustc_session::config::EntryFnType;
 use rustc_span::source_map::{dummy_spanned, respan, Span, Spanned, DUMMY_SP};
 use smallvec::SmallVec;
@@ -638,6 +638,35 @@ impl<'a, 'tcx> MirVisitor<'tcx> for MirNeighborCollector<'a, 'tcx> {
         self.super_rvalue(rvalue, location);
     }
 
+    /// This does not walk the constant, as it has been handled entirely here and trying
+    /// to walk it would attempt to evaluate the `ty::Const` inside, which doesn't necessarily
+    /// work, as some constants cannot be represented in the type system.
+    fn visit_constant(&mut self, constant: &mir::Constant<'tcx>, location: Location) {
+        let literal = self.monomorphize(constant.literal);
+        let val = match literal {
+            mir::ConstantKind::Val(val, _) => val,
+            mir::ConstantKind::Ty(ct) => match ct.val {
+                ty::ConstKind::Value(val) => val,
+                ty::ConstKind::Unevaluated(ct) => {
+                    let param_env = ty::ParamEnv::reveal_all();
+                    match self.tcx.const_eval_resolve(param_env, ct, None) {
+                        // The `monomorphize` call should have evaluated that constant already.
+                        Ok(val) => val,
+                        Err(ErrorHandled::Reported(ErrorReported) | ErrorHandled::Linted) => return,
+                        Err(ErrorHandled::TooGeneric) => span_bug!(
+                            self.body.source_info(location).span,
+                            "collection encountered polymorphic constant: {:?}",
+                            literal
+                        ),
+                    }
+                }
+                _ => return,
+            },
+        };
+        collect_const_value(self.tcx, val, self.output);
+        self.visit_ty(literal.ty(), TyContext::Location(location));
+    }
+
     fn visit_const(&mut self, constant: &&'tcx ty::Const<'tcx>, location: Location) {
         debug!("visiting const {:?} @ {:?}", *constant, location);
 

compiler/rustc_mir/src/util/pretty.rs

@@ -452,7 +452,11 @@ impl Visitor<'tcx> for ExtraComments<'tcx> {
                 match literal {
                     ConstantKind::Ty(literal) => self.push(&format!("+ literal: {:?}", literal)),
                     ConstantKind::Val(val, ty) => {
-                        self.push(&format!("+ literal: {:?}, {}", val, ty))
+                        // To keep the diffs small, we render this almost like we render ty::Const
+                        self.push(&format!(
+                            "+ literal: Const {{ ty: {}, val: Value({:?}) }}",
+                            ty, val
+                        ))
                     }
                 }
             }