Auto merge of #55716 - RalfJung:escape-to-raw, r=oli-obk

Add escape-to-raw MIR statement

Add a new MIR "ghost state statement": Escaping a ptr to permit raw accesses.

~~This includes #55549, [click here](https://github.com/RalfJung/rust/compare/miri-visitor...RalfJung:escape-to-raw) for just the new commits.~~

3 files changed, 16 insertions, 1 deletions

diff --git a/src/librustc/ich/impls_mir.rs b/src/librustc/ich/impls_mir.rs
index c42c19e82c7..d6ad74f16a9 100644
--- a/src/librustc/ich/impls_mir.rs
+++ b/src/librustc/ich/impls_mir.rs
@@ -220,6 +220,9 @@ for mir::StatementKind<'gcx> {
             mir::StatementKind::EndRegion(ref region_scope) => {
                 region_scope.hash_stable(hcx, hasher);
             }
+            mir::StatementKind::EscapeToRaw(ref place) => {
+                place.hash_stable(hcx, hasher);
+            }
             mir::StatementKind::Retag { fn_entry, ref place } => {
                 fn_entry.hash_stable(hcx, hasher);
                 place.hash_stable(hcx, hasher);
diff --git a/src/librustc/mir/mod.rs b/src/librustc/mir/mod.rs
index 548d0e0c790..d8e45c881f5 100644
--- a/src/librustc/mir/mod.rs
+++ b/src/librustc/mir/mod.rs
@@ -1782,6 +1782,13 @@ pub enum StatementKind<'tcx> {
         place: Place<'tcx>,
     },
 
+    /// Escape the given reference to a raw pointer, so that it can be accessed
+    /// without precise provenance tracking. These statements are currently only interpreted
+    /// by miri and only generated when "-Z mir-emit-retag" is passed.
+    /// See <https://internals.rust-lang.org/t/stacked-borrows-an-aliasing-model-for-rust/8153/>
+    /// for more details.
+    EscapeToRaw(Operand<'tcx>),
+
     /// Mark one terminating point of a region scope (i.e. static region).
     /// (The starting point(s) arise implicitly from borrows.)
     EndRegion(region::Scope),
@@ -1843,6 +1850,7 @@ impl<'tcx> Debug for Statement<'tcx> {
             EndRegion(ref ce) => write!(fmt, "EndRegion({})", ty::ReScope(*ce)),
             Retag { fn_entry, ref place } =>
                 write!(fmt, "Retag({}{:?})", if fn_entry { "[fn entry] " } else { "" }, place),
+            EscapeToRaw(ref place) => write!(fmt, "EscapeToRaw({:?})", place),
             StorageLive(ref place) => write!(fmt, "StorageLive({:?})", place),
             StorageDead(ref place) => write!(fmt, "StorageDead({:?})", place),
             SetDiscriminant {
@@ -3019,6 +3027,7 @@ EnumTypeFoldableImpl! {
         (StatementKind::StorageDead)(a),
         (StatementKind::InlineAsm) { asm, outputs, inputs },
         (StatementKind::Retag) { fn_entry, place },
+        (StatementKind::EscapeToRaw)(place),
         (StatementKind::EndRegion)(a),
         (StatementKind::AscribeUserType)(a, v, b),
         (StatementKind::Nop),
diff --git a/src/librustc/mir/visit.rs b/src/librustc/mir/visit.rs
index c130e047e47..2a994ee0509 100644
--- a/src/librustc/mir/visit.rs
+++ b/src/librustc/mir/visit.rs
@@ -385,6 +385,9 @@ macro_rules! make_mir_visitor {
                             location
                         );
                     }
+                    StatementKind::EscapeToRaw(ref $($mutability)* op) => {
+                        self.visit_operand(op, location);
+                    }
                     StatementKind::StorageLive(ref $($mutability)* local) => {
                         self.visit_local(
                             local,
@@ -1022,7 +1025,7 @@ pub enum MutatingUseContext<'tcx> {
     ///     f(&mut x.y);
     ///
     Projection,
-    /// Retagging (updating the "Stacked Borrows" tag)
+    /// Retagging, a "Stacked Borrows" shadow state operation
     Retag,
 }