Add a stable MIR visitor

Add a few utility functions as well and extend most `mir` and `ty`
ADTs to implement `PartialEq` and `Eq`.

compiler/rustc_smir/src/rustc_smir/mod.rs

@@ -216,6 +216,12 @@ impl<'tcx> Context for TablesWrapper<'tcx> {
         tables.create_def_id(def_id)
     }
 
+    fn instance_mangled_name(&self, def: InstanceDef) -> String {
+        let tables = self.0.borrow_mut();
+        let instance = tables.instances[def];
+        tables.tcx.symbol_name(instance).name.to_string()
+    }
+
     fn mono_instance(&self, item: stable_mir::CrateItem) -> stable_mir::mir::mono::Instance {
         let mut tables = self.0.borrow_mut();
         let def_id = tables[item.0];

compiler/stable_mir/src/lib.rs

@@ -103,8 +103,6 @@ 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(Copy, Clone, PartialEq, Eq, Debug)]
 pub struct CrateItem(pub DefId);
 
@@ -224,6 +222,9 @@ pub trait Context {
     /// 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;
@@ -259,7 +260,7 @@ pub fn with<R>(f: impl FnOnce(&dyn Context) -> R) -> R {
 }
 
 /// 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 {

compiler/stable_mir/src/mir.rs

@@ -1,4 +1,6 @@
 mod body;
 pub mod mono;
+pub mod visit;
 
 pub use body::*;
+pub use visit::MirVisitor;

compiler/stable_mir/src/mir/body.rs

@@ -1,6 +1,6 @@
-use crate::ty::{AdtDef, ClosureDef, Const, CoroutineDef, 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)]
@@ -12,10 +12,10 @@ pub struct Body {
     // 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.
-    locals: LocalDecls,
+    pub(super) locals: LocalDecls,
 
     // The number of arguments this function takes.
-    arg_count: usize,
+    pub(super) arg_count: usize,
 }
 
 impl Body {
@@ -35,7 +35,7 @@ impl Body {
 
     /// Return local that holds this function's return value.
     pub fn ret_local(&self) -> &LocalDecl {
-        &self.locals[0]
+        &self.locals[RETURN_LOCAL]
     }
 
     /// Locals in `self` that correspond to this function's arguments.
@@ -60,7 +60,7 @@ impl Body {
 
 type LocalDecls = Vec<LocalDecl>;
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct LocalDecl {
     pub ty: Ty,
     pub span: Span,
@@ -72,13 +72,13 @@ pub struct BasicBlock {
     pub terminator: Terminator,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct Terminator {
     pub kind: TerminatorKind,
     pub span: Span,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum TerminatorKind {
     Goto {
         target: usize,
@@ -122,7 +122,7 @@ pub enum TerminatorKind {
     },
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct InlineAsmOperand {
     pub in_value: Option<Operand>,
     pub out_place: Option<Place>,
@@ -131,7 +131,7 @@ pub struct InlineAsmOperand {
     pub raw_rpr: String,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum UnwindAction {
     Continue,
     Unreachable,
@@ -139,7 +139,7 @@ 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),
@@ -151,7 +151,7 @@ pub enum AssertMessage {
     MisalignedPointerDereference { required: Operand, found: Operand },
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum BinOp {
     Add,
     AddUnchecked,
@@ -177,20 +177,20 @@ pub enum BinOp {
     Offset,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum UnOp {
     Not,
     Neg,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum CoroutineKind {
     Async(CoroutineSource),
     Coroutine,
     Gen(CoroutineSource),
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum CoroutineSource {
     Block,
     Closure,
@@ -204,7 +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),
@@ -214,7 +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,
@@ -222,7 +222,7 @@ pub enum RetagKind {
     Default,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash)]
 pub enum Variance {
     Covariant,
     Invariant,
@@ -230,26 +230,26 @@ 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)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct Statement {
     pub kind: StatementKind,
     pub span: Span,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum StatementKind {
     Assign(Place, Rvalue),
     FakeRead(FakeReadCause, Place),
@@ -266,7 +266,7 @@ pub enum StatementKind {
     Nop,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum Rvalue {
     /// Creates a pointer with the indicated mutability to the place.
     ///
@@ -378,7 +378,7 @@ pub enum Rvalue {
     Use(Operand),
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum AggregateKind {
     Array(Ty),
     Tuple,
@@ -387,21 +387,21 @@ pub enum AggregateKind {
     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,
@@ -409,6 +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.
@@ -416,20 +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,
@@ -446,26 +448,26 @@ 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,
@@ -492,7 +494,7 @@ pub enum PointerCoercion {
     Unsize,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum CastKind {
     PointerExposeAddress,
     PointerFromExposedAddress,
@@ -507,7 +509,7 @@ 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,

compiler/stable_mir/src/mir/mono.rs

@@ -42,6 +42,10 @@ impl Instance {
         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| {

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
+    }
+}

compiler/stable_mir/src/ty.rs

@@ -22,12 +22,12 @@ impl Ty {
 }
 
 /// Represents a constant in MIR or from the Type system.
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct Const {
     /// The constant kind.
-    kind: ConstantKind,
+    pub(crate) kind: ConstantKind,
     /// The constant type.
-    ty: Ty,
+    pub(crate) ty: Ty,
     /// Used for internal tracking of the internal constant.
     pub id: ConstId,
 }
@@ -54,12 +54,12 @@ 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),
@@ -70,7 +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,
@@ -79,7 +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,
@@ -87,7 +87,7 @@ 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,
@@ -127,7 +127,7 @@ pub struct LineInfo {
     pub end_col: usize,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum TyKind {
     RigidTy(RigidTy),
     Alias(AliasKind, AliasTy),
@@ -135,7 +135,7 @@ pub enum TyKind {
     Bound(usize, BoundTy),
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum RigidTy {
     Bool,
     Char,
@@ -236,7 +236,7 @@ pub struct ImplDef(pub DefId);
 pub struct RegionDef(pub DefId);
 
 /// A list of generic arguments.
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct GenericArgs(pub Vec<GenericArgKind>);
 
 impl std::ops::Index<ParamTy> for GenericArgs {
@@ -255,7 +255,7 @@ impl std::ops::Index<ParamConst> for GenericArgs {
     }
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum GenericArgKind {
     Lifetime(Region),
     Type(Ty),
@@ -284,13 +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,
@@ -298,7 +298,7 @@ pub enum AliasKind {
     Weak,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct AliasTy {
     pub def_id: AliasDef,
     pub args: GenericArgs,
@@ -306,7 +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,
@@ -345,18 +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),
@@ -369,46 +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,
@@ -424,14 +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,
@@ -439,7 +439,7 @@ pub struct Allocation {
     pub mutability: Mutability,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum ConstantKind {
     Allocated(Allocation),
     Unevaluated(UnevaluatedConst),
@@ -449,13 +449,13 @@ pub enum ConstantKind {
     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,
@@ -469,7 +469,7 @@ pub enum TraitSpecializationKind {
     AlwaysApplicable,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub struct TraitDecl {
     pub def_id: TraitDef,
     pub unsafety: Safety,
@@ -500,13 +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,
@@ -517,14 +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,
@@ -538,7 +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),
@@ -550,7 +550,7 @@ pub enum PredicateKind {
     AliasRelate(TermKind, TermKind, AliasRelationDirection),
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum ClauseKind {
     Trait(TraitPredicate),
     RegionOutlives(RegionOutlivesPredicate),
@@ -561,50 +561,50 @@ 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,

tests/ui-fulldeps/stable-mir/smir_visitor.rs

@@ -0,0 +1,148 @@
+// run-pass
+//! Sanity check Stable MIR Visitor
+
+// ignore-stage1
+// ignore-cross-compile
+// ignore-remote
+// ignore-windows-gnu mingw has troubles with linking https://github.com/rust-lang/rust/pull/116837
+// edition: 2021
+
+#![feature(rustc_private)]
+#![feature(assert_matches)]
+#![feature(control_flow_enum)]
+
+extern crate rustc_middle;
+#[macro_use]
+extern crate rustc_smir;
+extern crate rustc_driver;
+extern crate rustc_interface;
+extern crate stable_mir;
+
+use std::collections::HashSet;
+use rustc_middle::ty::TyCtxt;
+use rustc_smir::rustc_internal;
+use stable_mir::*;
+use stable_mir::mir::MirVisitor;
+use std::io::Write;
+use std::ops::ControlFlow;
+
+const CRATE_NAME: &str = "input";
+
+fn test_visitor(_tcx: TyCtxt<'_>) -> ControlFlow<()> {
+    let main_fn = stable_mir::entry_fn();
+    let main_body = main_fn.unwrap().body();
+    let main_visitor = TestVisitor::collect(&main_body);
+    assert!(main_visitor.ret_val.is_some());
+    assert!(main_visitor.args.is_empty());
+    assert!(main_visitor.tys.contains(&main_visitor.ret_val.unwrap().ty));
+    assert!(!main_visitor.calls.is_empty());
+
+    let exit_fn = main_visitor.calls.last().unwrap();
+    assert!(exit_fn.mangled_name().contains("exit_fn"), "Unexpected last function: {exit_fn:?}");
+
+    let exit_body = exit_fn.body();
+    let exit_visitor = TestVisitor::collect(&exit_body);
+    assert!(exit_visitor.ret_val.is_some());
+    assert_eq!(exit_visitor.args.len(), 1);
+    assert!(exit_visitor.tys.contains(&exit_visitor.ret_val.unwrap().ty));
+    assert!(exit_visitor.tys.contains(&exit_visitor.args[0].ty));
+    ControlFlow::Continue(())
+}
+
+struct TestVisitor<'a> {
+    pub body: &'a mir::Body,
+    pub tys: HashSet<ty::Ty>,
+    pub ret_val: Option<mir::LocalDecl>,
+    pub args: Vec<mir::LocalDecl>,
+    pub calls: Vec<mir::mono::Instance>
+}
+
+impl<'a> TestVisitor<'a> {
+    fn collect(body: &'a mir::Body) -> TestVisitor<'a> {
+        let mut visitor = TestVisitor {
+            body: &body,
+            tys: Default::default(),
+            ret_val: None,
+            args: vec![],
+            calls: vec![],
+        };
+        visitor.visit_body(&body);
+        visitor
+    }
+}
+
+impl<'a> mir::MirVisitor for TestVisitor<'a> {
+    fn visit_ty(&mut self, ty: &ty::Ty, _location: mir::visit::Location) {
+        self.tys.insert(*ty);
+        self.super_ty(ty)
+    }
+
+    fn visit_ret_decl(&mut self, local: mir::Local, decl: &mir::LocalDecl) {
+        assert!(local == mir::RETURN_LOCAL);
+        assert!(self.ret_val.is_none());
+        self.ret_val = Some(decl.clone());
+        self.super_ret_decl(local, decl);
+    }
+
+    fn visit_arg_decl(&mut self, local: mir::Local, decl: &mir::LocalDecl) {
+        self.args.push(decl.clone());
+        assert_eq!(local, self.args.len());
+        self.super_arg_decl(local, decl);
+    }
+
+    fn visit_terminator(&mut self, term: &mir::Terminator, location: mir::visit::Location) {
+        if let mir::TerminatorKind::Call { func, .. } = &term.kind {
+            let ty::TyKind::RigidTy(ty) = func.ty(self.body.locals()).kind() else { unreachable!
+            () };
+            let ty::RigidTy::FnDef(def, args) = ty else { unreachable!() };
+            self.calls.push(mir::mono::Instance::resolve(def, &args).unwrap());
+        }
+        self.super_terminator(term, location);
+    }
+}
+
+/// This test will generate and analyze a dummy crate using the stable mir.
+/// For that, it will first write the dummy crate into a file.
+/// Then it will create a `StableMir` using custom arguments and then
+/// it will run the compiler.
+fn main() {
+    let path = "sim_visitor_input.rs";
+    generate_input(&path).unwrap();
+    let args = vec![
+        "rustc".to_string(),
+        "-Cpanic=abort".to_string(),
+        "--crate-name".to_string(),
+        CRATE_NAME.to_string(),
+        path.to_string(),
+    ];
+    run!(args, tcx, test_visitor(tcx)).unwrap();
+}
+
+fn generate_input(path: &str) -> std::io::Result<()> {
+    let mut file = std::fs::File::create(path)?;
+    write!(
+        file,
+        r#"
+    fn main() -> std::process::ExitCode {{
+        let inputs = Inputs::new();
+        let total = inputs.values.iter().sum();
+        exit_fn(total)
+    }}
+
+    fn exit_fn(code: u8) -> std::process::ExitCode {{
+        std::process::ExitCode::from(code)
+    }}
+
+    struct Inputs {{
+        values: [u8; 3],
+    }}
+
+    impl Inputs {{
+        fn new() -> Inputs {{
+            Inputs {{ values: [0, 1, 2] }}
+        }}
+    }}
+    "#
+    )?;
+    Ok(())
+}