Merging upstream version 1.75.0+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

9 files changed, 958 insertions, 406 deletions

diff --git a/compiler/stable_mir/src/error.rs b/compiler/stable_mir/src/error.rs
new file mode 100644
index 000000000..199106914
--- /dev/null
+++ b/compiler/stable_mir/src/error.rs
@@ -0,0 +1,76 @@
+//! When things go wrong, we need some error handling.
+//! There are a few different types of errors in StableMIR:
+//!
+//! - [CompilerError]: This represents errors that can be raised when invoking the compiler.
+//! - [Error]: Generic error that represents the reason why a request that could not be fulfilled.
+
+use std::convert::From;
+use std::fmt::{Debug, Display, Formatter};
+use std::{error, fmt};
+
+/// An error type used to represent an error that has already been reported by the compiler.
+#[derive(Clone, Copy, PartialEq, Eq)]
+pub enum CompilerError<T> {
+    /// Internal compiler error (I.e.: Compiler crashed).
+    ICE,
+    /// Compilation failed.
+    CompilationFailed,
+    /// Compilation was interrupted.
+    Interrupted(T),
+    /// Compilation skipped. This happens when users invoke rustc to retrieve information such as
+    /// --version.
+    Skipped,
+}
+
+/// A generic error to represent an API request that cannot be fulfilled.
+#[derive(Debug)]
+pub struct Error(String);
+
+impl Error {
+    pub(crate) fn new(msg: String) -> Self {
+        Self(msg)
+    }
+}
+
+impl From<&str> for Error {
+    fn from(value: &str) -> Self {
+        Self(value.into())
+    }
+}
+
+impl Display for Error {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        Display::fmt(&self.0, f)
+    }
+}
+
+impl<T> Display for CompilerError<T>
+where
+    T: Display,
+{
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        match self {
+            CompilerError::ICE => write!(f, "Internal Compiler Error"),
+            CompilerError::CompilationFailed => write!(f, "Compilation Failed"),
+            CompilerError::Interrupted(reason) => write!(f, "Compilation Interrupted: {reason}"),
+            CompilerError::Skipped => write!(f, "Compilation Skipped"),
+        }
+    }
+}
+
+impl<T> Debug for CompilerError<T>
+where
+    T: Debug,
+{
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        match self {
+            CompilerError::ICE => write!(f, "Internal Compiler Error"),
+            CompilerError::CompilationFailed => write!(f, "Compilation Failed"),
+            CompilerError::Interrupted(reason) => write!(f, "Compilation Interrupted: {reason:?}"),
+            CompilerError::Skipped => write!(f, "Compilation Skipped"),
+        }
+    }
+}
+
+impl error::Error for Error {}
+impl<T> error::Error for CompilerError<T> where T: Display + Debug {}
diff --git a/compiler/stable_mir/src/fold.rs b/compiler/stable_mir/src/fold.rs
deleted file mode 100644
index 6471b2c2a..000000000
--- a/compiler/stable_mir/src/fold.rs
+++ /dev/null
@@ -1,245 +0,0 @@
-use std::ops::ControlFlow;
-
-use crate::Opaque;
-
-use super::ty::{
-    Allocation, Binder, Const, ConstDef, ConstantKind, ExistentialPredicate, FnSig, GenericArgKind,
-    GenericArgs, Promoted, Region, RigidTy, TermKind, Ty, TyKind, UnevaluatedConst,
-};
-
-pub trait Folder: Sized {
-    type Break;
-    fn fold_ty(&mut self, ty: &Ty) -> ControlFlow<Self::Break, Ty> {
-        ty.super_fold(self)
-    }
-    fn fold_const(&mut self, c: &Const) -> ControlFlow<Self::Break, Const> {
-        c.super_fold(self)
-    }
-    fn fold_reg(&mut self, reg: &Region) -> ControlFlow<Self::Break, Region> {
-        reg.super_fold(self)
-    }
-}
-
-pub trait Foldable: Sized + Clone {
-    fn fold<V: Folder>(&self, folder: &mut V) -> ControlFlow<V::Break, Self> {
-        self.super_fold(folder)
-    }
-    fn super_fold<V: Folder>(&self, folder: &mut V) -> ControlFlow<V::Break, Self>;
-}
-
-impl Foldable for Ty {
-    fn fold<V: Folder>(&self, folder: &mut V) -> ControlFlow<V::Break, Self> {
-        folder.fold_ty(self)
-    }
-    fn super_fold<V: Folder>(&self, folder: &mut V) -> ControlFlow<V::Break, Self> {
-        let mut kind = self.kind();
-        match &mut kind {
-            super::ty::TyKind::RigidTy(ty) => *ty = ty.fold(folder)?,
-            super::ty::TyKind::Alias(_, alias) => alias.args = alias.args.fold(folder)?,
-            super::ty::TyKind::Param(_) => {}
-            super::ty::TyKind::Bound(_, _) => {}
-        }
-        ControlFlow::Continue(kind.into())
-    }
-}
-
-impl Foldable for Const {
-    fn fold<V: Folder>(&self, folder: &mut V) -> ControlFlow<V::Break, Self> {
-        folder.fold_const(self)
-    }
-    fn super_fold<V: Folder>(&self, folder: &mut V) -> ControlFlow<V::Break, Self> {
-        let mut this = self.clone();
-        match &mut this.literal {
-            super::ty::ConstantKind::Allocated(alloc) => *alloc = alloc.fold(folder)?,
-            super::ty::ConstantKind::Unevaluated(uv) => *uv = uv.fold(folder)?,
-            super::ty::ConstantKind::Param(_) => {}
-        }
-        this.ty = this.ty.fold(folder)?;
-        ControlFlow::Continue(this)
-    }
-}
-
-impl Foldable for Opaque {
-    fn super_fold<V: Folder>(&self, _folder: &mut V) -> ControlFlow<V::Break, Self> {
-        ControlFlow::Continue(self.clone())
-    }
-}
-
-impl Foldable for Allocation {
-    fn super_fold<V: Folder>(&self, _folder: &mut V) -> ControlFlow<V::Break, Self> {
-        ControlFlow::Continue(self.clone())
-    }
-}
-
-impl Foldable for UnevaluatedConst {
-    fn super_fold<V: Folder>(&self, folder: &mut V) -> ControlFlow<V::Break, Self> {
-        let UnevaluatedConst { def, args, promoted } = self;
-        ControlFlow::Continue(UnevaluatedConst {
-            def: def.fold(folder)?,
-            args: args.fold(folder)?,
-            promoted: promoted.fold(folder)?,
-        })
-    }
-}
-
-impl Foldable for ConstDef {
-    fn super_fold<V: Folder>(&self, _folder: &mut V) -> ControlFlow<V::Break, Self> {
-        ControlFlow::Continue(*self)
-    }
-}
-
-impl<T: Foldable> Foldable for Option<T> {
-    fn super_fold<V: Folder>(&self, folder: &mut V) -> ControlFlow<V::Break, Self> {
-        ControlFlow::Continue(match self {
-            Some(val) => Some(val.fold(folder)?),
-            None => None,
-        })
-    }
-}
-
-impl Foldable for Promoted {
-    fn super_fold<V: Folder>(&self, _folder: &mut V) -> ControlFlow<V::Break, Self> {
-        ControlFlow::Continue(*self)
-    }
-}
-
-impl Foldable for GenericArgs {
-    fn super_fold<V: Folder>(&self, folder: &mut V) -> ControlFlow<V::Break, Self> {
-        ControlFlow::Continue(GenericArgs(self.0.fold(folder)?))
-    }
-}
-
-impl Foldable for Region {
-    fn fold<V: Folder>(&self, folder: &mut V) -> ControlFlow<V::Break, Self> {
-        folder.fold_reg(self)
-    }
-    fn super_fold<V: Folder>(&self, _: &mut V) -> ControlFlow<V::Break, Self> {
-        ControlFlow::Continue(self.clone())
-    }
-}
-
-impl Foldable for GenericArgKind {
-    fn super_fold<V: Folder>(&self, folder: &mut V) -> ControlFlow<V::Break, Self> {
-        let mut this = self.clone();
-        match &mut this {
-            GenericArgKind::Lifetime(lt) => *lt = lt.fold(folder)?,
-            GenericArgKind::Type(t) => *t = t.fold(folder)?,
-            GenericArgKind::Const(c) => *c = c.fold(folder)?,
-        }
-        ControlFlow::Continue(this)
-    }
-}
-
-impl Foldable for RigidTy {
-    fn super_fold<V: Folder>(&self, folder: &mut V) -> ControlFlow<V::Break, Self> {
-        let mut this = self.clone();
-        match &mut this {
-            RigidTy::Bool
-            | RigidTy::Char
-            | RigidTy::Int(_)
-            | RigidTy::Uint(_)
-            | RigidTy::Float(_)
-            | RigidTy::Never
-            | RigidTy::Foreign(_)
-            | RigidTy::Str => {}
-            RigidTy::Array(t, c) => {
-                *t = t.fold(folder)?;
-                *c = c.fold(folder)?;
-            }
-            RigidTy::Slice(inner) => *inner = inner.fold(folder)?,
-            RigidTy::RawPtr(ty, _) => *ty = ty.fold(folder)?,
-            RigidTy::Ref(reg, ty, _) => {
-                *reg = reg.fold(folder)?;
-                *ty = ty.fold(folder)?
-            }
-            RigidTy::FnDef(_, args) => *args = args.fold(folder)?,
-            RigidTy::FnPtr(sig) => *sig = sig.fold(folder)?,
-            RigidTy::Closure(_, args) => *args = args.fold(folder)?,
-            RigidTy::Generator(_, args, _) => *args = args.fold(folder)?,
-            RigidTy::Dynamic(pred, r, _) => {
-                *pred = pred.fold(folder)?;
-                *r = r.fold(folder)?;
-            }
-            RigidTy::Tuple(fields) => *fields = fields.fold(folder)?,
-            RigidTy::Adt(_, args) => *args = args.fold(folder)?,
-        }
-        ControlFlow::Continue(this)
-    }
-}
-
-impl<T: Foldable> Foldable for Vec<T> {
-    fn super_fold<V: Folder>(&self, folder: &mut V) -> ControlFlow<V::Break, Self> {
-        let mut this = self.clone();
-        for arg in &mut this {
-            *arg = arg.fold(folder)?;
-        }
-        ControlFlow::Continue(this)
-    }
-}
-
-impl<T: Foldable> Foldable for Binder<T> {
-    fn super_fold<V: Folder>(&self, folder: &mut V) -> ControlFlow<V::Break, Self> {
-        ControlFlow::Continue(Self {
-            value: self.value.fold(folder)?,
-            bound_vars: self.bound_vars.clone(),
-        })
-    }
-}
-
-impl Foldable for ExistentialPredicate {
-    fn super_fold<V: Folder>(&self, folder: &mut V) -> ControlFlow<V::Break, Self> {
-        let mut this = self.clone();
-        match &mut this {
-            ExistentialPredicate::Trait(tr) => tr.generic_args = tr.generic_args.fold(folder)?,
-            ExistentialPredicate::Projection(p) => {
-                p.term = p.term.fold(folder)?;
-                p.generic_args = p.generic_args.fold(folder)?;
-            }
-            ExistentialPredicate::AutoTrait(_) => {}
-        }
-        ControlFlow::Continue(this)
-    }
-}
-
-impl Foldable for TermKind {
-    fn super_fold<V: Folder>(&self, folder: &mut V) -> ControlFlow<V::Break, Self> {
-        ControlFlow::Continue(match self {
-            TermKind::Type(t) => TermKind::Type(t.fold(folder)?),
-            TermKind::Const(c) => TermKind::Const(c.fold(folder)?),
-        })
-    }
-}
-
-impl Foldable for FnSig {
-    fn super_fold<V: Folder>(&self, folder: &mut V) -> ControlFlow<V::Break, Self> {
-        ControlFlow::Continue(Self {
-            inputs_and_output: self.inputs_and_output.fold(folder)?,
-            c_variadic: self.c_variadic,
-            unsafety: self.unsafety,
-            abi: self.abi.clone(),
-        })
-    }
-}
-
-pub enum Never {}
-
-/// In order to instantiate a `Foldable`'s generic parameters with specific arguments,
-/// `GenericArgs` can be used as a `Folder` that replaces all mentions of generic params
-/// with the entries in its list.
-impl Folder for GenericArgs {
-    type Break = Never;
-
-    fn fold_ty(&mut self, ty: &Ty) -> ControlFlow<Self::Break, Ty> {
-        ControlFlow::Continue(match ty.kind() {
-            TyKind::Param(p) => self[p],
-            _ => *ty,
-        })
-    }
-
-    fn fold_const(&mut self, c: &Const) -> ControlFlow<Self::Break, Const> {
-        ControlFlow::Continue(match &c.literal {
-            ConstantKind::Param(p) => self[p.clone()].clone(),
-            _ => c.clone(),
-        })
-    }
-}
diff --git a/compiler/stable_mir/src/lib.rs b/compiler/stable_mir/src/lib.rs
index 104985493..f316671b2 100644
--- a/compiler/stable_mir/src/lib.rs
+++ b/compiler/stable_mir/src/lib.rs
@@ -17,22 +17,29 @@
 //! The goal is to eventually be published on
 //! [crates.io](https://crates.io).
 
+use crate::mir::mono::InstanceDef;
+use crate::mir::Body;
 use std::cell::Cell;
 use std::fmt;
 use std::fmt::Debug;
 
 use self::ty::{
-    GenericPredicates, Generics, ImplDef, ImplTrait, Span, TraitDecl, TraitDef, Ty, TyKind,
+    GenericPredicates, Generics, ImplDef, ImplTrait, IndexedVal, LineInfo, Span, TraitDecl,
+    TraitDef, Ty, TyKind,
 };
 
 #[macro_use]
 extern crate scoped_tls;
 
-pub mod fold;
+pub mod error;
 pub mod mir;
 pub mod ty;
 pub mod visitor;
 
+pub use error::*;
+use mir::mono::Instance;
+use ty::{FnDef, GenericArgs};
+
 /// Use String for now but we should replace it.
 pub type Symbol = String;
 
@@ -41,7 +48,7 @@ pub type CrateNum = usize;
 
 /// A unique identification number for each item accessible for the current compilation unit.
 #[derive(Clone, Copy, PartialEq, Eq)]
-pub struct DefId(pub usize);
+pub struct DefId(usize);
 
 impl Debug for DefId {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
@@ -52,9 +59,28 @@ impl Debug for DefId {
     }
 }
 
+impl IndexedVal for DefId {
+    fn to_val(index: usize) -> Self {
+        DefId(index)
+    }
+
+    fn to_index(&self) -> usize {
+        self.0
+    }
+}
+
 /// A unique identification number for each provenance
 #[derive(Clone, Copy, PartialEq, Eq, Debug)]
-pub struct AllocId(pub usize);
+pub struct AllocId(usize);
+
+impl IndexedVal for AllocId {
+    fn to_val(index: usize) -> Self {
+        AllocId(index)
+    }
+    fn to_index(&self) -> usize {
+        self.0
+    }
+}
 
 /// A list of crate items.
 pub type CrateItems = Vec<CrateItem>;
@@ -65,20 +91,6 @@ pub type TraitDecls = Vec<TraitDef>;
 /// A list of impl trait decls.
 pub type ImplTraitDecls = Vec<ImplDef>;
 
-/// An error type used to represent an error that has already been reported by the compiler.
-#[derive(Clone, Copy, Debug, PartialEq, Eq)]
-pub enum CompilerError<T> {
-    /// Internal compiler error (I.e.: Compiler crashed).
-    ICE,
-    /// Compilation failed.
-    CompilationFailed,
-    /// Compilation was interrupted.
-    Interrupted(T),
-    /// Compilation skipped. This happens when users invoke rustc to retrieve information such as
-    /// --version.
-    Skipped,
-}
-
 /// Holds information about a crate.
 #[derive(Clone, PartialEq, Eq, Debug)]
 pub struct Crate {
@@ -88,11 +100,10 @@ pub struct Crate {
 }
 
 pub type DefKind = Opaque;
+pub type Filename = Opaque;
 
 /// Holds information about an item in the crate.
-/// For now, it only stores the item DefId. Use functions inside `rustc_internal` module to
-/// use this item.
-#[derive(Clone, PartialEq, Eq, Debug)]
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
 pub struct CrateItem(pub DefId);
 
 impl CrateItem {
@@ -111,6 +122,10 @@ impl CrateItem {
     pub fn kind(&self) -> DefKind {
         with(|cx| cx.def_kind(self.0))
     }
+
+    pub fn requires_monomorphization(&self) -> bool {
+        with(|cx| cx.requires_monomorphization(self.0))
+    }
 }
 
 /// Return the function where execution starts if the current
@@ -125,9 +140,9 @@ pub fn local_crate() -> Crate {
     with(|cx| cx.local_crate())
 }
 
-/// Try to find a crate with the given name.
-pub fn find_crate(name: &str) -> Option<Crate> {
-    with(|cx| cx.find_crate(name))
+/// Try to find a crate or crates if multiple crates exist from given name.
+pub fn find_crates(name: &str) -> Vec<Crate> {
+    with(|cx| cx.find_crates(name))
 }
 
 /// Try to find a crate with the given name.
@@ -157,72 +172,95 @@ pub fn trait_impl(trait_impl: &ImplDef) -> ImplTrait {
 }
 
 pub trait Context {
-    fn entry_fn(&mut self) -> Option<CrateItem>;
+    fn entry_fn(&self) -> Option<CrateItem>;
     /// Retrieve all items of the local crate that have a MIR associated with them.
-    fn all_local_items(&mut self) -> CrateItems;
-    fn mir_body(&mut self, item: DefId) -> mir::Body;
-    fn all_trait_decls(&mut self) -> TraitDecls;
-    fn trait_decl(&mut self, trait_def: &TraitDef) -> TraitDecl;
-    fn all_trait_impls(&mut self) -> ImplTraitDecls;
-    fn trait_impl(&mut self, trait_impl: &ImplDef) -> ImplTrait;
-    fn generics_of(&mut self, def_id: DefId) -> Generics;
-    fn predicates_of(&mut self, def_id: DefId) -> GenericPredicates;
-    fn explicit_predicates_of(&mut self, def_id: DefId) -> GenericPredicates;
+    fn all_local_items(&self) -> CrateItems;
+    fn mir_body(&self, item: DefId) -> mir::Body;
+    fn all_trait_decls(&self) -> TraitDecls;
+    fn trait_decl(&self, trait_def: &TraitDef) -> TraitDecl;
+    fn all_trait_impls(&self) -> ImplTraitDecls;
+    fn trait_impl(&self, trait_impl: &ImplDef) -> ImplTrait;
+    fn generics_of(&self, def_id: DefId) -> Generics;
+    fn predicates_of(&self, def_id: DefId) -> GenericPredicates;
+    fn explicit_predicates_of(&self, def_id: DefId) -> GenericPredicates;
     /// Get information about the local crate.
     fn local_crate(&self) -> Crate;
     /// Retrieve a list of all external crates.
     fn external_crates(&self) -> Vec<Crate>;
 
     /// Find a crate with the given name.
-    fn find_crate(&self, name: &str) -> Option<Crate>;
+    fn find_crates(&self, name: &str) -> Vec<Crate>;
 
-    /// Prints the name of given `DefId`
+    /// Returns the name of given `DefId`
     fn name_of_def_id(&self, def_id: DefId) -> String;
 
-    /// Prints a human readable form of `Span`
-    fn print_span(&self, span: Span) -> String;
+    /// Returns printable, human readable form of `Span`
+    fn span_to_string(&self, span: Span) -> String;
 
-    /// Prints the kind of given `DefId`
-    fn def_kind(&mut self, def_id: DefId) -> DefKind;
+    /// Return filename from given `Span`, for diagnostic purposes
+    fn get_filename(&self, span: &Span) -> Filename;
+
+    /// Return lines corresponding to this `Span`
+    fn get_lines(&self, span: &Span) -> LineInfo;
+
+    /// Returns the `kind` of given `DefId`
+    fn def_kind(&self, def_id: DefId) -> DefKind;
 
     /// `Span` of an item
-    fn span_of_an_item(&mut self, def_id: DefId) -> Span;
+    fn span_of_an_item(&self, def_id: DefId) -> Span;
 
     /// Obtain the representation of a type.
-    fn ty_kind(&mut self, ty: Ty) -> TyKind;
+    fn ty_kind(&self, ty: Ty) -> TyKind;
+
+    /// Get the body of an Instance.
+    /// FIXME: Monomorphize the body.
+    fn instance_body(&self, instance: InstanceDef) -> Body;
 
-    /// Create a new `Ty` from scratch without information from rustc.
-    fn mk_ty(&mut self, kind: TyKind) -> Ty;
+    /// Get the instance type with generic substitutions applied and lifetimes erased.
+    fn instance_ty(&self, instance: InstanceDef) -> Ty;
+
+    /// Get the instance.
+    fn instance_def_id(&self, instance: InstanceDef) -> DefId;
+
+    /// Get the instance mangled name.
+    fn instance_mangled_name(&self, instance: InstanceDef) -> String;
+
+    /// Convert a non-generic crate item into an instance.
+    /// This function will panic if the item is generic.
+    fn mono_instance(&self, item: CrateItem) -> Instance;
+
+    /// Item requires monomorphization.
+    fn requires_monomorphization(&self, def_id: DefId) -> bool;
+
+    /// Resolve an instance from the given function definition and generic arguments.
+    fn resolve_instance(&self, def: FnDef, args: &GenericArgs) -> Option<Instance>;
 }
 
 // A thread local variable that stores a pointer to the tables mapping between TyCtxt
 // datastructures and stable MIR datastructures
-scoped_thread_local! (static TLV: Cell<*mut ()>);
+scoped_thread_local! (static TLV: Cell<*const ()>);
 
-pub fn run(mut context: impl Context, f: impl FnOnce()) {
+pub fn run(context: &dyn Context, f: impl FnOnce()) {
     assert!(!TLV.is_set());
-    fn g<'a>(mut context: &mut (dyn Context + 'a), f: impl FnOnce()) {
-        let ptr: *mut () = &mut context as *mut &mut _ as _;
-        TLV.set(&Cell::new(ptr), || {
-            f();
-        });
-    }
-    g(&mut context, f);
+    let ptr: *const () = &context as *const &_ as _;
+    TLV.set(&Cell::new(ptr), || {
+        f();
+    });
 }
 
 /// Loads the current context and calls a function with it.
 /// Do not nest these, as that will ICE.
-pub fn with<R>(f: impl FnOnce(&mut dyn Context) -> R) -> R {
+pub fn with<R>(f: impl FnOnce(&dyn Context) -> R) -> R {
     assert!(TLV.is_set());
     TLV.with(|tlv| {
         let ptr = tlv.get();
         assert!(!ptr.is_null());
-        f(unsafe { *(ptr as *mut &mut dyn Context) })
+        f(unsafe { *(ptr as *const &dyn Context) })
     })
 }
 
 /// A type that provides internal information but that can still be used for debug purpose.
-#[derive(Clone)]
+#[derive(Clone, Eq, PartialEq)]
 pub struct Opaque(String);
 
 impl std::fmt::Display for Opaque {
diff --git a/compiler/stable_mir/src/mir.rs b/compiler/stable_mir/src/mir.rs
index a9dbc3463..2e1714b49 100644
--- a/compiler/stable_mir/src/mir.rs
+++ b/compiler/stable_mir/src/mir.rs
@@ -1,3 +1,6 @@
 mod body;
+pub mod mono;
+pub mod visit;
 
 pub use body::*;
+pub use visit::MirVisitor;
diff --git a/compiler/stable_mir/src/mir/body.rs b/compiler/stable_mir/src/mir/body.rs
index f93a1a3a9..069337836 100644
--- a/compiler/stable_mir/src/mir/body.rs
+++ b/compiler/stable_mir/src/mir/body.rs
@@ -1,11 +1,69 @@
-use crate::ty::{AdtDef, ClosureDef, Const, GeneratorDef, GenericArgs, Movability, Region};
+use crate::ty::{AdtDef, ClosureDef, Const, CoroutineDef, GenericArgs, Movability, Region, Ty};
 use crate::Opaque;
-use crate::{ty::Ty, Span};
+use crate::Span;
 
+/// The SMIR representation of a single function.
 #[derive(Clone, Debug)]
 pub struct Body {
     pub blocks: Vec<BasicBlock>,
-    pub locals: Vec<Ty>,
+
+    // Declarations of locals within the function.
+    //
+    // The first local is the return value pointer, followed by `arg_count`
+    // locals for the function arguments, followed by any user-declared
+    // variables and temporaries.
+    pub(super) locals: LocalDecls,
+
+    // The number of arguments this function takes.
+    pub(super) arg_count: usize,
+}
+
+impl Body {
+    /// Constructs a `Body`.
+    ///
+    /// A constructor is required to build a `Body` from outside the crate
+    /// because the `arg_count` and `locals` fields are private.
+    pub fn new(blocks: Vec<BasicBlock>, locals: LocalDecls, arg_count: usize) -> Self {
+        // If locals doesn't contain enough entries, it can lead to panics in
+        // `ret_local`, `arg_locals`, and `inner_locals`.
+        assert!(
+            locals.len() > arg_count,
+            "A Body must contain at least a local for the return value and each of the function's arguments"
+        );
+        Self { blocks, locals, arg_count }
+    }
+
+    /// Return local that holds this function's return value.
+    pub fn ret_local(&self) -> &LocalDecl {
+        &self.locals[RETURN_LOCAL]
+    }
+
+    /// Locals in `self` that correspond to this function's arguments.
+    pub fn arg_locals(&self) -> &[LocalDecl] {
+        &self.locals[1..][..self.arg_count]
+    }
+
+    /// Inner locals for this function. These are the locals that are
+    /// neither the return local nor the argument locals.
+    pub fn inner_locals(&self) -> &[LocalDecl] {
+        &self.locals[self.arg_count + 1..]
+    }
+
+    /// Convenience function to get all the locals in this function.
+    ///
+    /// Locals are typically accessed via the more specific methods `ret_local`,
+    /// `arg_locals`, and `inner_locals`.
+    pub fn locals(&self) -> &[LocalDecl] {
+        &self.locals
+    }
+}
+
+type LocalDecls = Vec<LocalDecl>;
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct LocalDecl {
+    pub ty: Ty,
+    pub span: Span,
 }
 
 #[derive(Clone, Debug)]
@@ -14,8 +72,14 @@ pub struct BasicBlock {
     pub terminator: Terminator,
 }
 
-#[derive(Clone, Debug)]
-pub enum Terminator {
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct Terminator {
+    pub kind: TerminatorKind,
+    pub span: Span,
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub enum TerminatorKind {
     Goto {
         target: usize,
     },
@@ -47,7 +111,7 @@ pub enum Terminator {
         target: usize,
         unwind: UnwindAction,
     },
-    GeneratorDrop,
+    CoroutineDrop,
     InlineAsm {
         template: String,
         operands: Vec<InlineAsmOperand>,
@@ -58,7 +122,7 @@ pub enum Terminator {
     },
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct InlineAsmOperand {
     pub in_value: Option<Operand>,
     pub out_place: Option<Place>,
@@ -67,7 +131,7 @@ pub struct InlineAsmOperand {
     pub raw_rpr: String,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum UnwindAction {
     Continue,
     Unreachable,
@@ -75,19 +139,19 @@ pub enum UnwindAction {
     Cleanup(usize),
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum AssertMessage {
     BoundsCheck { len: Operand, index: Operand },
     Overflow(BinOp, Operand, Operand),
     OverflowNeg(Operand),
     DivisionByZero(Operand),
     RemainderByZero(Operand),
-    ResumedAfterReturn(GeneratorKind),
-    ResumedAfterPanic(GeneratorKind),
+    ResumedAfterReturn(CoroutineKind),
+    ResumedAfterPanic(CoroutineKind),
     MisalignedPointerDereference { required: Operand, found: Operand },
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum BinOp {
     Add,
     AddUnchecked,
@@ -113,20 +177,21 @@ pub enum BinOp {
     Offset,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum UnOp {
     Not,
     Neg,
 }
 
-#[derive(Clone, Debug)]
-pub enum GeneratorKind {
-    Async(AsyncGeneratorKind),
-    Gen,
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub enum CoroutineKind {
+    Async(CoroutineSource),
+    Coroutine,
+    Gen(CoroutineSource),
 }
 
-#[derive(Clone, Debug)]
-pub enum AsyncGeneratorKind {
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub enum CoroutineSource {
     Block,
     Closure,
     Fn,
@@ -139,7 +204,7 @@ pub(crate) type LocalDefId = Opaque;
 pub(crate) type Coverage = Opaque;
 
 /// The FakeReadCause describes the type of pattern why a FakeRead statement exists.
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum FakeReadCause {
     ForMatchGuard,
     ForMatchedPlace(LocalDefId),
@@ -149,7 +214,7 @@ pub enum FakeReadCause {
 }
 
 /// Describes what kind of retag is to be performed
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash)]
 pub enum RetagKind {
     FnEntry,
     TwoPhase,
@@ -157,7 +222,7 @@ pub enum RetagKind {
     Default,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash)]
 pub enum Variance {
     Covariant,
     Invariant,
@@ -165,21 +230,27 @@ pub enum Variance {
     Bivariant,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct CopyNonOverlapping {
     pub src: Operand,
     pub dst: Operand,
     pub count: Operand,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum NonDivergingIntrinsic {
     Assume(Operand),
     CopyNonOverlapping(CopyNonOverlapping),
 }
 
-#[derive(Clone, Debug)]
-pub enum Statement {
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct Statement {
+    pub kind: StatementKind,
+    pub span: Span,
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub enum StatementKind {
     Assign(Place, Rvalue),
     FakeRead(FakeReadCause, Place),
     SetDiscriminant { place: Place, variant_index: VariantIdx },
@@ -195,7 +266,7 @@ pub enum Statement {
     Nop,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum Rvalue {
     /// Creates a pointer with the indicated mutability to the place.
     ///
@@ -209,8 +280,8 @@ pub enum Rvalue {
     /// `dest = Foo { x: ..., y: ... }` from `dest.x = ...; dest.y = ...;` in the case that `Foo`
     /// has a destructor.
     ///
-    /// Disallowed after deaggregation for all aggregate kinds except `Array` and `Generator`. After
-    /// generator lowering, `Generator` aggregate kinds are disallowed too.
+    /// Disallowed after deaggregation for all aggregate kinds except `Array` and `Coroutine`. After
+    /// coroutine lowering, `Coroutine` aggregate kinds are disallowed too.
     Aggregate(AggregateKind, Vec<Operand>),
 
     /// * `Offset` has the same semantics as `<*const T>::offset`, except that the second
@@ -307,29 +378,30 @@ pub enum Rvalue {
     Use(Operand),
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum AggregateKind {
     Array(Ty),
     Tuple,
     Adt(AdtDef, VariantIdx, GenericArgs, Option<UserTypeAnnotationIndex>, Option<FieldIdx>),
     Closure(ClosureDef, GenericArgs),
-    Generator(GeneratorDef, GenericArgs, Movability),
+    Coroutine(CoroutineDef, GenericArgs, Movability),
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum Operand {
     Copy(Place),
     Move(Place),
     Constant(Constant),
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct Place {
     pub local: Local,
+    /// projection out of a place (access a field, deref a pointer, etc)
     pub projection: String,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct UserTypeProjection {
     pub base: UserTypeAnnotationIndex,
     pub projection: String,
@@ -337,6 +409,8 @@ pub struct UserTypeProjection {
 
 pub type Local = usize;
 
+pub const RETURN_LOCAL: Local = 0;
+
 type FieldIdx = usize;
 
 /// The source-order index of a variant in a type.
@@ -344,20 +418,20 @@ pub type VariantIdx = usize;
 
 type UserTypeAnnotationIndex = usize;
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct Constant {
     pub span: Span,
     pub user_ty: Option<UserTypeAnnotationIndex>,
     pub literal: Const,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct SwitchTarget {
     pub value: u128,
     pub target: usize,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum BorrowKind {
     /// Data must be immutable and is aliasable.
     Shared,
@@ -375,26 +449,26 @@ pub enum BorrowKind {
     },
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum MutBorrowKind {
     Default,
     TwoPhaseBorrow,
     ClosureCapture,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, PartialEq, Eq)]
 pub enum Mutability {
     Not,
     Mut,
 }
 
-#[derive(Copy, Clone, Debug)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
 pub enum Safety {
     Unsafe,
     Normal,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum PointerCoercion {
     /// Go from a fn-item type to a fn-pointer type.
     ReifyFnPointer,
@@ -421,7 +495,7 @@ pub enum PointerCoercion {
     Unsize,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum CastKind {
     PointerExposeAddress,
     PointerFromExposedAddress,
@@ -436,12 +510,34 @@ pub enum CastKind {
     Transmute,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum NullOp {
     /// Returns the size of a value of that type.
     SizeOf,
     /// Returns the minimum alignment of a type.
     AlignOf,
     /// Returns the offset of a field.
-    OffsetOf(Vec<FieldIdx>),
+    OffsetOf(Vec<(VariantIdx, FieldIdx)>),
+}
+
+impl Operand {
+    pub fn ty(&self, locals: &[LocalDecl]) -> Ty {
+        match self {
+            Operand::Copy(place) | Operand::Move(place) => place.ty(locals),
+            Operand::Constant(c) => c.ty(),
+        }
+    }
+}
+
+impl Constant {
+    pub fn ty(&self) -> Ty {
+        self.literal.ty()
+    }
+}
+
+impl Place {
+    pub fn ty(&self, locals: &[LocalDecl]) -> Ty {
+        let _start_ty = locals[self.local].ty;
+        todo!("Implement projection")
+    }
 }
diff --git a/compiler/stable_mir/src/mir/mono.rs b/compiler/stable_mir/src/mir/mono.rs
new file mode 100644
index 000000000..8f5333498
--- /dev/null
+++ b/compiler/stable_mir/src/mir/mono.rs
@@ -0,0 +1,102 @@
+use crate::mir::Body;
+use crate::ty::{FnDef, GenericArgs, IndexedVal, Ty};
+use crate::{with, CrateItem, DefId, Error, Opaque};
+use std::fmt::Debug;
+
+#[derive(Clone, Debug)]
+pub enum MonoItem {
+    Fn(Instance),
+    Static(StaticDef),
+    GlobalAsm(Opaque),
+}
+
+#[derive(Copy, Clone, Debug)]
+pub struct Instance {
+    /// The type of instance.
+    pub kind: InstanceKind,
+    /// An ID used to get the instance definition from the compiler.
+    /// Do not use this field directly.
+    pub def: InstanceDef,
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum InstanceKind {
+    /// A user defined item.
+    Item,
+    /// A compiler intrinsic function.
+    Intrinsic,
+    /// A virtual function definition stored in a VTable.
+    Virtual,
+    /// A compiler generated shim.
+    Shim,
+}
+
+impl Instance {
+    /// Get the body of an Instance. The body will be eagerly monomorphized.
+    pub fn body(&self) -> Body {
+        with(|context| context.instance_body(self.def))
+    }
+
+    /// Get the instance type with generic substitutions applied and lifetimes erased.
+    pub fn ty(&self) -> Ty {
+        with(|context| context.instance_ty(self.def))
+    }
+
+    pub fn mangled_name(&self) -> String {
+        with(|context| context.instance_mangled_name(self.def))
+    }
+
+    /// Resolve an instance starting from a function definition and generic arguments.
+    pub fn resolve(def: FnDef, args: &GenericArgs) -> Result<Instance, crate::Error> {
+        with(|context| {
+            context.resolve_instance(def, args).ok_or_else(|| {
+                crate::Error::new(format!("Failed to resolve `{def:?}` with `{args:?}`"))
+            })
+        })
+    }
+}
+
+/// Try to convert a crate item into an instance.
+/// The item cannot be generic in order to be converted into an instance.
+impl TryFrom<CrateItem> for Instance {
+    type Error = crate::Error;
+
+    fn try_from(item: CrateItem) -> Result<Self, Self::Error> {
+        with(|context| {
+            if !context.requires_monomorphization(item.0) {
+                Ok(context.mono_instance(item))
+            } else {
+                Err(Error::new("Item requires monomorphization".to_string()))
+            }
+        })
+    }
+}
+
+/// Try to convert an instance into a crate item.
+/// Only user defined instances can be converted.
+impl TryFrom<Instance> for CrateItem {
+    type Error = crate::Error;
+
+    fn try_from(value: Instance) -> Result<Self, Self::Error> {
+        if value.kind == InstanceKind::Item {
+            Ok(CrateItem(with(|context| context.instance_def_id(value.def))))
+        } else {
+            Err(Error::new(format!("Item kind `{:?}` cannot be converted", value.kind)))
+        }
+    }
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct InstanceDef(usize);
+
+#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+pub struct StaticDef(pub DefId);
+
+impl IndexedVal for InstanceDef {
+    fn to_val(index: usize) -> Self {
+        InstanceDef(index)
+    }
+    fn to_index(&self) -> usize {
+        self.0
+    }
+}
diff --git a/compiler/stable_mir/src/mir/visit.rs b/compiler/stable_mir/src/mir/visit.rs
new file mode 100644
index 000000000..806dced71
--- /dev/null
+++ b/compiler/stable_mir/src/mir/visit.rs
@@ -0,0 +1,414 @@
+//! # The Stable MIR Visitor
+//!
+//! ## Overview
+//!
+//! We currently only support an immutable visitor.
+//! The structure of this visitor is similar to the ones internal to `rustc`,
+//! and it follows the following conventions:
+//!
+//! For every mir item, the trait has a `visit_<item>` and a `super_<item>` method.
+//! - `visit_<item>`, by default, calls `super_<item>`
+//! - `super_<item>`, by default, destructures the `<item>` and calls `visit_<sub_item>` for
+//!   all sub-items that compose the original item.
+//!
+//! In order to implement a visitor, override the `visit_*` methods for the types you are
+//! interested in analyzing, and invoke (within that method call)
+//! `self.super_*` to continue to the traverse.
+//! Avoid calling `super` methods in other circumstances.
+//!
+//! For the most part, we do not destructure things external to the
+//! MIR, e.g., types, spans, etc, but simply visit them and stop.
+//! This avoids duplication with other visitors like `TypeFoldable`.
+//!
+//! ## Updating
+//!
+//! The code is written in a very deliberate style intended to minimize
+//! the chance of things being overlooked.
+//!
+//! Use pattern matching to reference fields and ensure that all
+//! matches are exhaustive.
+//!
+//! For this to work, ALL MATCHES MUST BE EXHAUSTIVE IN FIELDS AND VARIANTS.
+//! That means you never write `..` to skip over fields, nor do you write `_`
+//! to skip over variants in a `match`.
+//!
+//! The only place that `_` is acceptable is to match a field (or
+//! variant argument) that does not require visiting.
+
+use crate::mir::*;
+use crate::ty::{Const, GenericArgs, Region, Ty};
+use crate::{Opaque, Span};
+
+pub trait MirVisitor {
+    fn visit_body(&mut self, body: &Body) {
+        self.super_body(body)
+    }
+
+    fn visit_basic_block(&mut self, bb: &BasicBlock) {
+        self.super_basic_block(bb)
+    }
+
+    fn visit_ret_decl(&mut self, local: Local, decl: &LocalDecl) {
+        self.super_ret_decl(local, decl)
+    }
+
+    fn visit_arg_decl(&mut self, local: Local, decl: &LocalDecl) {
+        self.super_arg_decl(local, decl)
+    }
+
+    fn visit_local_decl(&mut self, local: Local, decl: &LocalDecl) {
+        self.super_local_decl(local, decl)
+    }
+
+    fn visit_statement(&mut self, stmt: &Statement, location: Location) {
+        self.super_statement(stmt, location)
+    }
+
+    fn visit_terminator(&mut self, term: &Terminator, location: Location) {
+        self.super_terminator(term, location)
+    }
+
+    fn visit_span(&mut self, span: &Span) {
+        self.super_span(span)
+    }
+
+    fn visit_place(&mut self, place: &Place, ptx: PlaceContext, location: Location) {
+        self.super_place(place, ptx, location)
+    }
+
+    fn visit_local(&mut self, local: &Local, ptx: PlaceContext, location: Location) {
+        let _ = (local, ptx, location);
+    }
+
+    fn visit_rvalue(&mut self, rvalue: &Rvalue, location: Location) {
+        self.super_rvalue(rvalue, location)
+    }
+
+    fn visit_operand(&mut self, operand: &Operand, location: Location) {
+        self.super_operand(operand, location)
+    }
+
+    fn visit_user_type_projection(&mut self, projection: &UserTypeProjection) {
+        self.super_user_type_projection(projection)
+    }
+
+    fn visit_ty(&mut self, ty: &Ty, location: Location) {
+        let _ = location;
+        self.super_ty(ty)
+    }
+
+    fn visit_constant(&mut self, constant: &Constant, location: Location) {
+        self.super_constant(constant, location)
+    }
+
+    fn visit_const(&mut self, constant: &Const, location: Location) {
+        self.super_const(constant, location)
+    }
+
+    fn visit_region(&mut self, region: &Region, location: Location) {
+        let _ = location;
+        self.super_region(region)
+    }
+
+    fn visit_args(&mut self, args: &GenericArgs, location: Location) {
+        let _ = location;
+        self.super_args(args)
+    }
+
+    fn visit_assert_msg(&mut self, msg: &AssertMessage, location: Location) {
+        self.super_assert_msg(msg, location)
+    }
+
+    fn super_body(&mut self, body: &Body) {
+        let Body { blocks, locals: _, arg_count } = body;
+
+        for bb in blocks {
+            self.visit_basic_block(bb);
+        }
+
+        self.visit_ret_decl(RETURN_LOCAL, body.ret_local());
+
+        for (idx, arg) in body.arg_locals().iter().enumerate() {
+            self.visit_arg_decl(idx + 1, arg)
+        }
+
+        let local_start = arg_count + 1;
+        for (idx, arg) in body.arg_locals().iter().enumerate() {
+            self.visit_local_decl(idx + local_start, arg)
+        }
+    }
+
+    fn super_basic_block(&mut self, bb: &BasicBlock) {
+        let BasicBlock { statements, terminator } = bb;
+        for stmt in statements {
+            self.visit_statement(stmt, Location(stmt.span));
+        }
+        self.visit_terminator(terminator, Location(terminator.span));
+    }
+
+    fn super_local_decl(&mut self, local: Local, decl: &LocalDecl) {
+        let _ = local;
+        let LocalDecl { ty, span } = decl;
+        self.visit_ty(ty, Location(*span));
+    }
+
+    fn super_ret_decl(&mut self, local: Local, decl: &LocalDecl) {
+        self.super_local_decl(local, decl)
+    }
+
+    fn super_arg_decl(&mut self, local: Local, decl: &LocalDecl) {
+        self.super_local_decl(local, decl)
+    }
+
+    fn super_statement(&mut self, stmt: &Statement, location: Location) {
+        let Statement { kind, span } = stmt;
+        self.visit_span(span);
+        match kind {
+            StatementKind::Assign(place, rvalue) => {
+                self.visit_place(place, PlaceContext::MUTATING, location);
+                self.visit_rvalue(rvalue, location);
+            }
+            StatementKind::FakeRead(_, place) => {
+                self.visit_place(place, PlaceContext::NON_MUTATING, location);
+            }
+            StatementKind::SetDiscriminant { place, .. } => {
+                self.visit_place(place, PlaceContext::MUTATING, location);
+            }
+            StatementKind::Deinit(place) => {
+                self.visit_place(place, PlaceContext::MUTATING, location);
+            }
+            StatementKind::StorageLive(local) => {
+                self.visit_local(local, PlaceContext::NON_USE, location);
+            }
+            StatementKind::StorageDead(local) => {
+                self.visit_local(local, PlaceContext::NON_USE, location);
+            }
+            StatementKind::Retag(_, place) => {
+                self.visit_place(place, PlaceContext::MUTATING, location);
+            }
+            StatementKind::PlaceMention(place) => {
+                self.visit_place(place, PlaceContext::NON_MUTATING, location);
+            }
+            StatementKind::AscribeUserType { place, projections, variance: _ } => {
+                self.visit_place(place, PlaceContext::NON_USE, location);
+                self.visit_user_type_projection(projections);
+            }
+            StatementKind::Coverage(coverage) => visit_opaque(coverage),
+            StatementKind::Intrinsic(intrisic) => match intrisic {
+                NonDivergingIntrinsic::Assume(operand) => {
+                    self.visit_operand(operand, location);
+                }
+                NonDivergingIntrinsic::CopyNonOverlapping(CopyNonOverlapping {
+                    src,
+                    dst,
+                    count,
+                }) => {
+                    self.visit_operand(src, location);
+                    self.visit_operand(dst, location);
+                    self.visit_operand(count, location);
+                }
+            },
+            StatementKind::ConstEvalCounter => {}
+            StatementKind::Nop => {}
+        }
+    }
+
+    fn super_terminator(&mut self, term: &Terminator, location: Location) {
+        let Terminator { kind, span } = term;
+        self.visit_span(&span);
+        match kind {
+            TerminatorKind::Goto { .. }
+            | TerminatorKind::Resume
+            | TerminatorKind::Abort
+            | TerminatorKind::Unreachable
+            | TerminatorKind::CoroutineDrop => {}
+            TerminatorKind::Assert { cond, expected: _, msg, target: _, unwind: _ } => {
+                self.visit_operand(cond, location);
+                self.visit_assert_msg(msg, location);
+            }
+            TerminatorKind::Drop { place, target: _, unwind: _ } => {
+                self.visit_place(place, PlaceContext::MUTATING, location);
+            }
+            TerminatorKind::Call { func, args, destination, target: _, unwind: _ } => {
+                self.visit_operand(func, location);
+                for arg in args {
+                    self.visit_operand(arg, location);
+                }
+                self.visit_place(destination, PlaceContext::MUTATING, location);
+            }
+            TerminatorKind::InlineAsm { operands, .. } => {
+                for op in operands {
+                    let InlineAsmOperand { in_value, out_place, raw_rpr: _ } = op;
+                    if let Some(input) = in_value {
+                        self.visit_operand(input, location);
+                    }
+                    if let Some(output) = out_place {
+                        self.visit_place(output, PlaceContext::MUTATING, location);
+                    }
+                }
+            }
+            TerminatorKind::Return => {
+                let local = RETURN_LOCAL;
+                self.visit_local(&local, PlaceContext::NON_MUTATING, location);
+            }
+            TerminatorKind::SwitchInt { discr, targets: _, otherwise: _ } => {
+                self.visit_operand(discr, location);
+            }
+        }
+    }
+
+    fn super_span(&mut self, span: &Span) {
+        let _ = span;
+    }
+
+    fn super_place(&mut self, place: &Place, ptx: PlaceContext, location: Location) {
+        let _ = location;
+        let _ = ptx;
+        visit_opaque(&Opaque(place.projection.clone()));
+    }
+
+    fn super_rvalue(&mut self, rvalue: &Rvalue, location: Location) {
+        match rvalue {
+            Rvalue::AddressOf(mutability, place) => {
+                let pcx = PlaceContext { is_mut: *mutability == Mutability::Mut };
+                self.visit_place(place, pcx, location);
+            }
+            Rvalue::Aggregate(_, operands) => {
+                for op in operands {
+                    self.visit_operand(op, location);
+                }
+            }
+            Rvalue::BinaryOp(_, lhs, rhs) | Rvalue::CheckedBinaryOp(_, lhs, rhs) => {
+                self.visit_operand(lhs, location);
+                self.visit_operand(rhs, location);
+            }
+            Rvalue::Cast(_, op, ty) => {
+                self.visit_operand(op, location);
+                self.visit_ty(ty, location);
+            }
+            Rvalue::CopyForDeref(place) | Rvalue::Discriminant(place) | Rvalue::Len(place) => {
+                self.visit_place(place, PlaceContext::NON_MUTATING, location);
+            }
+            Rvalue::Ref(region, kind, place) => {
+                self.visit_region(region, location);
+                let pcx = PlaceContext { is_mut: matches!(kind, BorrowKind::Mut { .. }) };
+                self.visit_place(place, pcx, location);
+            }
+            Rvalue::Repeat(op, constant) => {
+                self.visit_operand(op, location);
+                self.visit_const(constant, location);
+            }
+            Rvalue::ShallowInitBox(op, ty) => {
+                self.visit_ty(ty, location);
+                self.visit_operand(op, location)
+            }
+            Rvalue::ThreadLocalRef(_) => {}
+            Rvalue::NullaryOp(_, ty) => {
+                self.visit_ty(ty, location);
+            }
+            Rvalue::UnaryOp(_, op) | Rvalue::Use(op) => {
+                self.visit_operand(op, location);
+            }
+        }
+    }
+
+    fn super_operand(&mut self, operand: &Operand, location: Location) {
+        match operand {
+            Operand::Copy(place) | Operand::Move(place) => {
+                self.visit_place(place, PlaceContext::NON_MUTATING, location)
+            }
+            Operand::Constant(constant) => {
+                self.visit_constant(constant, location);
+            }
+        }
+    }
+
+    fn super_user_type_projection(&mut self, projection: &UserTypeProjection) {
+        // This is a no-op on mir::Visitor.
+        let _ = projection;
+    }
+
+    fn super_ty(&mut self, ty: &Ty) {
+        let _ = ty;
+    }
+
+    fn super_constant(&mut self, constant: &Constant, location: Location) {
+        let Constant { span, user_ty: _, literal } = constant;
+        self.visit_span(span);
+        self.visit_const(literal, location);
+    }
+
+    fn super_const(&mut self, constant: &Const, location: Location) {
+        let Const { kind: _, ty, id: _ } = constant;
+        self.visit_ty(ty, location);
+    }
+
+    fn super_region(&mut self, region: &Region) {
+        let _ = region;
+    }
+
+    fn super_args(&mut self, args: &GenericArgs) {
+        let _ = args;
+    }
+
+    fn super_assert_msg(&mut self, msg: &AssertMessage, location: Location) {
+        match msg {
+            AssertMessage::BoundsCheck { len, index } => {
+                self.visit_operand(len, location);
+                self.visit_operand(index, location);
+            }
+            AssertMessage::Overflow(_, left, right) => {
+                self.visit_operand(left, location);
+                self.visit_operand(right, location);
+            }
+            AssertMessage::OverflowNeg(op)
+            | AssertMessage::DivisionByZero(op)
+            | AssertMessage::RemainderByZero(op) => {
+                self.visit_operand(op, location);
+            }
+            AssertMessage::ResumedAfterReturn(_) | AssertMessage::ResumedAfterPanic(_) => { //nothing to visit
+            }
+            AssertMessage::MisalignedPointerDereference { required, found } => {
+                self.visit_operand(required, location);
+                self.visit_operand(found, location);
+            }
+        }
+    }
+}
+
+/// This function is a no-op that gets used to ensure this visitor is kept up-to-date.
+///
+/// The idea is that whenever we replace an Opaque type by a real type, the compiler will fail
+/// when trying to invoke `visit_opaque`.
+///
+/// If you are here because your compilation is broken, replace the failing call to `visit_opaque()`
+/// by a `visit_<CONSTRUCT>` for your construct.
+fn visit_opaque(_: &Opaque) {}
+
+/// The location of a statement / terminator in the code and the CFG.
+#[derive(Clone, Copy, PartialEq, Eq)]
+pub struct Location(Span);
+
+impl Location {
+    pub fn span(&self) -> Span {
+        self.0
+    }
+}
+
+/// Information about a place's usage.
+#[derive(Copy, Clone, PartialEq, Eq, Hash)]
+pub struct PlaceContext {
+    /// Whether the access is mutable or not. Keep this private so we can increment the type in a
+    /// backward compatible manner.
+    is_mut: bool,
+}
+
+impl PlaceContext {
+    const MUTATING: Self = PlaceContext { is_mut: true };
+    const NON_MUTATING: Self = PlaceContext { is_mut: false };
+    const NON_USE: Self = PlaceContext { is_mut: false };
+
+    pub fn is_mutating(&self) -> bool {
+        self.is_mut
+    }
+}
diff --git a/compiler/stable_mir/src/ty.rs b/compiler/stable_mir/src/ty.rs
index 6029e3c11..5dfaa0fd8 100644
--- a/compiler/stable_mir/src/ty.rs
+++ b/compiler/stable_mir/src/ty.rs
@@ -3,10 +3,10 @@ use super::{
     mir::{Body, Mutability},
     with, AllocId, DefId, Symbol,
 };
-use crate::Opaque;
+use crate::{Filename, Opaque};
 use std::fmt::{self, Debug, Formatter};
 
-#[derive(Copy, Clone)]
+#[derive(Copy, Clone, Eq, PartialEq, Hash)]
 pub struct Ty(pub usize);
 
 impl Debug for Ty {
@@ -21,26 +21,45 @@ impl Ty {
     }
 }
 
-impl From<TyKind> for Ty {
-    fn from(value: TyKind) -> Self {
-        with(|context| context.mk_ty(value))
+/// Represents a constant in MIR or from the Type system.
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct Const {
+    /// The constant kind.
+    pub(crate) kind: ConstantKind,
+    /// The constant type.
+    pub(crate) ty: Ty,
+    /// Used for internal tracking of the internal constant.
+    pub id: ConstId,
+}
+
+impl Const {
+    /// Build a constant. Note that this should only be used by the compiler.
+    pub fn new(kind: ConstantKind, ty: Ty, id: ConstId) -> Const {
+        Const { kind, ty, id }
     }
-}
 
-#[derive(Debug, Clone)]
-pub struct Const {
-    pub literal: ConstantKind,
-    pub ty: Ty,
+    /// Retrieve the constant kind.
+    pub fn kind(&self) -> &ConstantKind {
+        &self.kind
+    }
+
+    /// Get the constant type.
+    pub fn ty(&self) -> Ty {
+        self.ty
+    }
 }
 
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct ConstId(pub usize);
+
 type Ident = Opaque;
 
-#[derive(Debug, Clone)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct Region {
     pub kind: RegionKind,
 }
 
-#[derive(Debug, Clone)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum RegionKind {
     ReEarlyBound(EarlyBoundRegion),
     ReLateBound(DebruijnIndex, BoundRegion),
@@ -51,7 +70,7 @@ pub enum RegionKind {
 
 pub(crate) type DebruijnIndex = u32;
 
-#[derive(Debug, Clone)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct EarlyBoundRegion {
     pub def_id: RegionDef,
     pub index: u32,
@@ -60,7 +79,7 @@ pub struct EarlyBoundRegion {
 
 pub(crate) type BoundVar = u32;
 
-#[derive(Debug, Clone)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct BoundRegion {
     pub var: BoundVar,
     pub kind: BoundRegionKind,
@@ -68,25 +87,47 @@ pub struct BoundRegion {
 
 pub(crate) type UniverseIndex = u32;
 
-#[derive(Debug, Clone)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct Placeholder<T> {
     pub universe: UniverseIndex,
     pub bound: T,
 }
 
 #[derive(Clone, Copy, PartialEq, Eq)]
-pub struct Span(pub usize);
+pub struct Span(usize);
 
 impl Debug for Span {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
         f.debug_struct("Span")
             .field("id", &self.0)
-            .field("repr", &with(|cx| cx.print_span(*self)))
+            .field("repr", &with(|cx| cx.span_to_string(*self)))
             .finish()
     }
 }
 
-#[derive(Clone, Debug)]
+impl Span {
+    /// Return filename for diagnostic purposes
+    pub fn get_filename(&self) -> Filename {
+        with(|c| c.get_filename(self))
+    }
+
+    /// Return lines that corespond to this `Span`
+    pub fn get_lines(&self) -> LineInfo {
+        with(|c| c.get_lines(&self))
+    }
+}
+
+#[derive(Clone, Copy, Debug)]
+/// Information you get from `Span` in a struct form.
+/// Line and col start from 1.
+pub struct LineInfo {
+    pub start_line: usize,
+    pub start_col: usize,
+    pub end_line: usize,
+    pub end_col: usize,
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum TyKind {
     RigidTy(RigidTy),
     Alias(AliasKind, AliasTy),
@@ -94,7 +135,7 @@ pub enum TyKind {
     Bound(usize, BoundTy),
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum RigidTy {
     Bool,
     Char,
@@ -111,7 +152,7 @@ pub enum RigidTy {
     FnDef(FnDef, GenericArgs),
     FnPtr(PolyFnSig),
     Closure(ClosureDef, GenericArgs),
-    Generator(GeneratorDef, GenericArgs, Movability),
+    Coroutine(CoroutineDef, GenericArgs, Movability),
     Dynamic(Vec<Binder<ExistentialPredicate>>, Region, DynKind),
     Never,
     Tuple(Vec<Ty>),
@@ -165,7 +206,7 @@ impl FnDef {
 pub struct ClosureDef(pub DefId);
 
 #[derive(Clone, Copy, PartialEq, Eq, Debug)]
-pub struct GeneratorDef(pub DefId);
+pub struct CoroutineDef(pub DefId);
 
 #[derive(Clone, Copy, PartialEq, Eq, Debug)]
 pub struct ParamDef(pub DefId);
@@ -194,7 +235,8 @@ pub struct ImplDef(pub DefId);
 #[derive(Clone, PartialEq, Eq, Debug)]
 pub struct RegionDef(pub DefId);
 
-#[derive(Clone, Debug)]
+/// A list of generic arguments.
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct GenericArgs(pub Vec<GenericArgKind>);
 
 impl std::ops::Index<ParamTy> for GenericArgs {
@@ -213,7 +255,7 @@ impl std::ops::Index<ParamConst> for GenericArgs {
     }
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum GenericArgKind {
     Lifetime(Region),
     Type(Ty),
@@ -242,13 +284,13 @@ impl GenericArgKind {
     }
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum TermKind {
     Type(Ty),
     Const(Const),
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum AliasKind {
     Projection,
     Inherent,
@@ -256,7 +298,7 @@ pub enum AliasKind {
     Weak,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct AliasTy {
     pub def_id: AliasDef,
     pub args: GenericArgs,
@@ -264,7 +306,7 @@ pub struct AliasTy {
 
 pub type PolyFnSig = Binder<FnSig>;
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct FnSig {
     pub inputs_and_output: Vec<Ty>,
     pub c_variadic: bool,
@@ -303,18 +345,18 @@ pub enum Abi {
     RiscvInterruptS,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct Binder<T> {
     pub value: T,
     pub bound_vars: Vec<BoundVariableKind>,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct EarlyBinder<T> {
     pub value: T,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum BoundVariableKind {
     Ty(BoundTyKind),
     Region(BoundRegionKind),
@@ -327,46 +369,46 @@ pub enum BoundTyKind {
     Param(ParamDef, String),
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum BoundRegionKind {
     BrAnon,
     BrNamed(BrNamedDef, String),
     BrEnv,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum DynKind {
     Dyn,
     DynStar,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum ExistentialPredicate {
     Trait(ExistentialTraitRef),
     Projection(ExistentialProjection),
     AutoTrait(TraitDef),
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct ExistentialTraitRef {
     pub def_id: TraitDef,
     pub generic_args: GenericArgs,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct ExistentialProjection {
     pub def_id: TraitDef,
     pub generic_args: GenericArgs,
     pub term: TermKind,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct ParamTy {
     pub index: u32,
     pub name: String,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct BoundTy {
     pub var: usize,
     pub kind: BoundTyKind,
@@ -382,14 +424,14 @@ pub type Promoted = u32;
 pub type InitMaskMaterialized = Vec<u64>;
 
 /// Stores the provenance information of pointers stored in memory.
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct ProvenanceMap {
     /// Provenance in this map applies from the given offset for an entire pointer-size worth of
     /// bytes. Two entries in this map are always at least a pointer size apart.
     pub ptrs: Vec<(Size, Prov)>,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct Allocation {
     pub bytes: Bytes,
     pub provenance: ProvenanceMap,
@@ -397,20 +439,23 @@ pub struct Allocation {
     pub mutability: Mutability,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum ConstantKind {
     Allocated(Allocation),
     Unevaluated(UnevaluatedConst),
     Param(ParamConst),
+    /// Store ZST constants.
+    /// We have to special handle these constants since its type might be generic.
+    ZeroSized,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct ParamConst {
     pub index: u32,
     pub name: String,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct UnevaluatedConst {
     pub def: ConstDef,
     pub args: GenericArgs,
@@ -424,7 +469,7 @@ pub enum TraitSpecializationKind {
     AlwaysApplicable,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct TraitDecl {
     pub def_id: TraitDef,
     pub unsafety: Safety,
@@ -455,13 +500,13 @@ impl TraitDecl {
 
 pub type ImplTrait = EarlyBinder<TraitRef>;
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct TraitRef {
     pub def_id: TraitDef,
     pub args: GenericArgs,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct Generics {
     pub parent: Option<GenericDef>,
     pub parent_count: usize,
@@ -472,14 +517,14 @@ pub struct Generics {
     pub host_effect_index: Option<usize>,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum GenericParamDefKind {
     Lifetime,
     Type { has_default: bool, synthetic: bool },
     Const { has_default: bool },
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct GenericParamDef {
     pub name: super::Symbol,
     pub def_id: GenericDef,
@@ -493,7 +538,7 @@ pub struct GenericPredicates {
     pub predicates: Vec<(PredicateKind, Span)>,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum PredicateKind {
     Clause(ClauseKind),
     ObjectSafe(TraitDef),
@@ -505,7 +550,7 @@ pub enum PredicateKind {
     AliasRelate(TermKind, TermKind, AliasRelationDirection),
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum ClauseKind {
     Trait(TraitPredicate),
     RegionOutlives(RegionOutlivesPredicate),
@@ -516,52 +561,75 @@ pub enum ClauseKind {
     ConstEvaluatable(Const),
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum ClosureKind {
     Fn,
     FnMut,
     FnOnce,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct SubtypePredicate {
     pub a: Ty,
     pub b: Ty,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct CoercePredicate {
     pub a: Ty,
     pub b: Ty,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum AliasRelationDirection {
     Equate,
     Subtype,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct TraitPredicate {
     pub trait_ref: TraitRef,
     pub polarity: ImplPolarity,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct OutlivesPredicate<A, B>(pub A, pub B);
 
 pub type RegionOutlivesPredicate = OutlivesPredicate<Region, Region>;
 pub type TypeOutlivesPredicate = OutlivesPredicate<Ty, Region>;
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct ProjectionPredicate {
     pub projection_ty: AliasTy,
     pub term: TermKind,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum ImplPolarity {
     Positive,
     Negative,
     Reservation,
 }
+
+pub trait IndexedVal {
+    fn to_val(index: usize) -> Self;
+
+    fn to_index(&self) -> usize;
+}
+
+macro_rules! index_impl {
+    ($name:ident) => {
+        impl IndexedVal for $name {
+            fn to_val(index: usize) -> Self {
+                $name(index)
+            }
+            fn to_index(&self) -> usize {
+                self.0
+            }
+        }
+    };
+}
+
+index_impl!(ConstId);
+index_impl!(Ty);
+index_impl!(Span);
diff --git a/compiler/stable_mir/src/visitor.rs b/compiler/stable_mir/src/visitor.rs
index 961009581..05e0b9b4d 100644
--- a/compiler/stable_mir/src/visitor.rs
+++ b/compiler/stable_mir/src/visitor.rs
@@ -47,12 +47,12 @@ impl Visitable for Const {
         visitor.visit_const(self)
     }
     fn super_visit<V: Visitor>(&self, visitor: &mut V) -> ControlFlow<V::Break> {
-        match &self.literal {
+        match &self.kind() {
             super::ty::ConstantKind::Allocated(alloc) => alloc.visit(visitor)?,
             super::ty::ConstantKind::Unevaluated(uv) => uv.visit(visitor)?,
-            super::ty::ConstantKind::Param(_) => {}
+            super::ty::ConstantKind::Param(_) | super::ty::ConstantKind::ZeroSized => {}
         }
-        self.ty.visit(visitor)
+        self.ty().visit(visitor)
     }
 }
 
@@ -148,7 +148,7 @@ impl Visitable for RigidTy {
             RigidTy::FnDef(_, args) => args.visit(visitor),
             RigidTy::FnPtr(sig) => sig.visit(visitor),
             RigidTy::Closure(_, args) => args.visit(visitor),
-            RigidTy::Generator(_, args, _) => args.visit(visitor),
+            RigidTy::Coroutine(_, args, _) => args.visit(visitor),
             RigidTy::Dynamic(pred, r, _) => {
                 pred.visit(visitor)?;
                 r.visit(visitor)