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](RalfJung/rust@miri-visitor...RalfJung:escape-to-raw) for just the new commits.~~

Author: bors

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);

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),

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,
 }
 

src/librustc_codegen_llvm/mir/statement.rs

@@ -105,8 +105,9 @@ impl FunctionCx<'a, 'll, 'tcx> {
                 bx
             }
             mir::StatementKind::FakeRead(..) |
-            mir::StatementKind::EndRegion(_) |
+            mir::StatementKind::EndRegion(..) |
             mir::StatementKind::Retag { .. } |
+            mir::StatementKind::EscapeToRaw { .. } |
             mir::StatementKind::AscribeUserType(..) |
             mir::StatementKind::Nop => bx,
         }

src/librustc_mir/borrow_check/mod.rs

@@ -599,6 +599,7 @@ impl<'cx, 'gcx, 'tcx> DataflowResultsConsumer<'cx, 'tcx> for MirBorrowckCtxt<'cx
             StatementKind::Nop
             | StatementKind::AscribeUserType(..)
             | StatementKind::Retag { .. }
+            | StatementKind::EscapeToRaw { .. }
             | StatementKind::StorageLive(..) => {
                 // `Nop`, `AscribeUserType`, `Retag`, and `StorageLive` are irrelevant
                 // to borrow check.

src/librustc_mir/borrow_check/nll/invalidation.rs

@@ -137,6 +137,7 @@ impl<'cx, 'tcx, 'gcx> Visitor<'tcx> for InvalidationGenerator<'cx, 'tcx, 'gcx> {
             StatementKind::Nop |
             StatementKind::AscribeUserType(..) |
             StatementKind::Retag { .. } |
+            StatementKind::EscapeToRaw { .. } |
             StatementKind::StorageLive(..) => {
                 // `Nop`, `AscribeUserType`, `Retag`, and `StorageLive` are irrelevant
                 // to borrow check.

src/librustc_mir/borrow_check/nll/type_check/mod.rs

@@ -1311,11 +1311,12 @@ impl<'a, 'gcx, 'tcx> TypeChecker<'a, 'gcx, 'tcx> {
                 }
             }
             StatementKind::FakeRead(..)
-            | StatementKind::StorageLive(_)
-            | StatementKind::StorageDead(_)
+            | StatementKind::StorageLive(..)
+            | StatementKind::StorageDead(..)
             | StatementKind::InlineAsm { .. }
             | StatementKind::EndRegion(_)
             | StatementKind::Retag { .. }
+            | StatementKind::EscapeToRaw { .. }
             | StatementKind::Nop => {}
         }
     }

src/librustc_mir/build/expr/as_place.rs

@@ -86,6 +86,9 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                 // region_scope=None so place indexes live forever. They are scalars so they
                 // do not need storage annotations, and they are often copied between
                 // places.
+                // Making this a *fresh* temporary also means we do not have to worry about
+                // the index changing later: Nothing will ever change this temporary.
+                // The "retagging" transformation (for Stacked Borrows) relies on this.
                 let idx = unpack!(block = this.as_temp(block, None, index, Mutability::Mut));
 
                 // bounds check:

src/librustc_mir/const_eval.rs

@@ -351,7 +351,6 @@ impl<'a, 'mir, 'tcx> interpret::Machine<'a, 'mir, 'tcx>
     type MemoryMap = FxHashMap<AllocId, (MemoryKind<!>, Allocation)>;
 
     const STATIC_KIND: Option<!> = None; // no copying of statics allowed
-    const ENABLE_PTR_TRACKING_HOOKS: bool = false; // we don't have no provenance
 
     #[inline(always)]
     fn enforce_validity(_ecx: &EvalContext<'a, 'mir, 'tcx, Self>) -> bool {

src/librustc_mir/dataflow/impls/borrows.rs

@@ -339,6 +339,7 @@ impl<'a, 'gcx, 'tcx> BitDenotation for Borrows<'a, 'gcx, 'tcx> {
             mir::StatementKind::SetDiscriminant { .. } |
             mir::StatementKind::StorageLive(..) |
             mir::StatementKind::Retag { .. } |
+            mir::StatementKind::EscapeToRaw { .. } |
             mir::StatementKind::AscribeUserType(..) |
             mir::StatementKind::Nop => {}