Auto merge of #55316 - RalfJung:retagging, r=oli-obk

Add Retagging statements

This adds a `Retag` statement kind to MIR, used to perform the retagging operation from [Stacked Borrows](https://www.ralfj.de/blog/2018/08/07/stacked-borrows.html). It also kills the old `Validate` statements that I added last year.

NOTE: This includes #55270. Only [these commits are new](RalfJung/rust@stacked-borrows-ng...RalfJung:retagging).

Author: bors

src/bootstrap/bin/rustc.rs

@@ -253,8 +253,15 @@ fn main() {
 
         // When running miri tests, we need to generate MIR for all libraries
         if env::var("TEST_MIRI").ok().map_or(false, |val| val == "true") {
+            // The flags here should be kept in sync with `add_miri_default_args`
+            // in miri's `src/lib.rs`.
             cmd.arg("-Zalways-encode-mir");
-            cmd.arg("-Zmir-emit-validate=1");
+            // These options are preferred by miri, to be able to perform better validation,
+            // but the bootstrap compiler might not understand them.
+            if stage != "0" {
+                cmd.arg("-Zmir-emit-retag");
+                cmd.arg("-Zmir-opt-level=0");
+            }
         }
 
         // Force all crates compiled by this compiler to (a) be unstable and (b)

src/librustc/ich/impls_mir.rs

@@ -257,9 +257,9 @@ for mir::StatementKind<'gcx> {
             mir::StatementKind::EndRegion(ref region_scope) => {
                 region_scope.hash_stable(hcx, hasher);
             }
-            mir::StatementKind::Validate(ref op, ref places) => {
-                op.hash_stable(hcx, hasher);
-                places.hash_stable(hcx, hasher);
+            mir::StatementKind::Retag { fn_entry, ref place } => {
+                fn_entry.hash_stable(hcx, hasher);
+                place.hash_stable(hcx, hasher);
             }
             mir::StatementKind::AscribeUserType(ref place, ref variance, ref c_ty) => {
                 place.hash_stable(hcx, hasher);
@@ -278,23 +278,6 @@ for mir::StatementKind<'gcx> {
 
 impl_stable_hash_for!(enum mir::FakeReadCause { ForMatchGuard, ForMatchedPlace, ForLet });
 
-impl<'a, 'gcx, T> HashStable<StableHashingContext<'a>>
-    for mir::ValidationOperand<'gcx, T>
-    where T: HashStable<StableHashingContext<'a>>
-{
-    fn hash_stable<W: StableHasherResult>(&self,
-                                          hcx: &mut StableHashingContext<'a>,
-                                          hasher: &mut StableHasher<W>)
-    {
-        self.place.hash_stable(hcx, hasher);
-        self.ty.hash_stable(hcx, hasher);
-        self.re.hash_stable(hcx, hasher);
-        self.mutbl.hash_stable(hcx, hasher);
-    }
-}
-
-impl_stable_hash_for!(enum mir::ValidationOp { Acquire, Release, Suspend(region_scope) });
-
 impl<'a, 'gcx> HashStable<StableHashingContext<'a>> for mir::Place<'gcx> {
     fn hash_stable<W: StableHasherResult>(&self,
                                           hcx: &mut StableHashingContext<'a>,

src/librustc/mir/mod.rs

@@ -1754,10 +1754,17 @@ pub enum StatementKind<'tcx> {
         inputs: Box<[Operand<'tcx>]>,
     },
 
-    /// Assert the given places to be valid inhabitants of their type.  These statements are
-    /// currently only interpreted by miri and only generated when "-Z mir-emit-validate" is passed.
-    /// See <https://internals.rust-lang.org/t/types-as-contracts/5562/73> for more details.
-    Validate(ValidationOp, Vec<ValidationOperand<'tcx, Place<'tcx>>>),
+    /// Retag references in the given place, ensuring they got fresh tags.  This is
+    /// part of the Stacked Borrows model. 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.
+    Retag {
+        /// `fn_entry` indicates whether this is the initial retag that happens in the
+        /// function prolog.
+        fn_entry: bool,
+        place: Place<'tcx>,
+    },
 
     /// Mark one terminating point of a region scope (i.e. static region).
     /// (The starting point(s) arise implicitly from borrows.)
@@ -1810,57 +1817,6 @@ pub enum FakeReadCause {
     ForLet,
 }
 
-/// The `ValidationOp` describes what happens with each of the operands of a
-/// `Validate` statement.
-#[derive(Copy, Clone, RustcEncodable, RustcDecodable, PartialEq, Eq)]
-pub enum ValidationOp {
-    /// Recursively traverse the place following the type and validate that all type
-    /// invariants are maintained.  Furthermore, acquire exclusive/read-only access to the
-    /// memory reachable from the place.
-    Acquire,
-    /// Recursive traverse the *mutable* part of the type and relinquish all exclusive
-    /// access.
-    Release,
-    /// Recursive traverse the *mutable* part of the type and relinquish all exclusive
-    /// access *until* the given region ends.  Then, access will be recovered.
-    Suspend(region::Scope),
-}
-
-impl Debug for ValidationOp {
-    fn fmt(&self, fmt: &mut Formatter<'_>) -> fmt::Result {
-        use self::ValidationOp::*;
-        match *self {
-            Acquire => write!(fmt, "Acquire"),
-            Release => write!(fmt, "Release"),
-            // (reuse lifetime rendering policy from ppaux.)
-            Suspend(ref ce) => write!(fmt, "Suspend({})", ty::ReScope(*ce)),
-        }
-    }
-}
-
-// This is generic so that it can be reused by miri
-#[derive(Clone, Hash, PartialEq, Eq, RustcEncodable, RustcDecodable)]
-pub struct ValidationOperand<'tcx, T> {
-    pub place: T,
-    pub ty: Ty<'tcx>,
-    pub re: Option<region::Scope>,
-    pub mutbl: hir::Mutability,
-}
-
-impl<'tcx, T: Debug> Debug for ValidationOperand<'tcx, T> {
-    fn fmt(&self, fmt: &mut Formatter<'_>) -> fmt::Result {
-        write!(fmt, "{:?}: {:?}", self.place, self.ty)?;
-        if let Some(ce) = self.re {
-            // (reuse lifetime rendering policy from ppaux.)
-            write!(fmt, "/{}", ty::ReScope(ce))?;
-        }
-        if let hir::MutImmutable = self.mutbl {
-            write!(fmt, " (imm)")?;
-        }
-        Ok(())
-    }
-}
-
 impl<'tcx> Debug for Statement<'tcx> {
     fn fmt(&self, fmt: &mut Formatter<'_>) -> fmt::Result {
         use self::StatementKind::*;
@@ -1869,7 +1825,8 @@ impl<'tcx> Debug for Statement<'tcx> {
             FakeRead(ref cause, ref place) => write!(fmt, "FakeRead({:?}, {:?})", cause, place),
             // (reuse lifetime rendering policy from ppaux.)
             EndRegion(ref ce) => write!(fmt, "EndRegion({})", ty::ReScope(*ce)),
-            Validate(ref op, ref places) => write!(fmt, "Validate({:?}, {:?})", op, places),
+            Retag { fn_entry, ref place } =>
+                write!(fmt, "Retag({}{:?})", if fn_entry { "[fn entry] " } else { "" }, place),
             StorageLive(ref place) => write!(fmt, "StorageLive({:?})", place),
             StorageDead(ref place) => write!(fmt, "StorageDead({:?})", place),
             SetDiscriminant {
@@ -2944,7 +2901,6 @@ CloneTypeFoldableAndLiftImpls! {
     SourceInfo,
     UpvarDecl,
     FakeReadCause,
-    ValidationOp,
     SourceScope,
     SourceScopeData,
     SourceScopeLocalData,
@@ -2997,12 +2953,6 @@ BraceStructTypeFoldableImpl! {
     }
 }
 
-BraceStructTypeFoldableImpl! {
-    impl<'tcx> TypeFoldable<'tcx> for ValidationOperand<'tcx, Place<'tcx>> {
-        place, ty, re, mutbl
-    }
-}
-
 BraceStructTypeFoldableImpl! {
     impl<'tcx> TypeFoldable<'tcx> for Statement<'tcx> {
         source_info, kind
@@ -3017,7 +2967,7 @@ EnumTypeFoldableImpl! {
         (StatementKind::StorageLive)(a),
         (StatementKind::StorageDead)(a),
         (StatementKind::InlineAsm) { asm, outputs, inputs },
-        (StatementKind::Validate)(a, b),
+        (StatementKind::Retag) { fn_entry, place },
         (StatementKind::EndRegion)(a),
         (StatementKind::AscribeUserType)(a, v, b),
         (StatementKind::Nop),

src/librustc/mir/visit.rs

@@ -152,6 +152,13 @@ macro_rules! make_mir_visitor {
                 self.super_ascribe_user_ty(place, variance, user_ty, location);
             }
 
+            fn visit_retag(&mut self,
+                           fn_entry: & $($mutability)* bool,
+                           place: & $($mutability)* Place<'tcx>,
+                           location: Location) {
+                self.super_retag(fn_entry, place, location);
+            }
+
             fn visit_place(&mut self,
                             place: & $($mutability)* Place<'tcx>,
                             context: PlaceContext<'tcx>,
@@ -371,17 +378,6 @@ macro_rules! make_mir_visitor {
                         );
                     }
                     StatementKind::EndRegion(_) => {}
-                    StatementKind::Validate(_, ref $($mutability)* places) => {
-                        for operand in places {
-                            self.visit_place(
-                                & $($mutability)* operand.place,
-                                PlaceContext::NonUse(NonUseContext::Validate),
-                                location
-                            );
-                            self.visit_ty(& $($mutability)* operand.ty,
-                                          TyContext::Location(location));
-                        }
-                    }
                     StatementKind::SetDiscriminant{ ref $($mutability)* place, .. } => {
                         self.visit_place(
                             place,
@@ -417,6 +413,10 @@ macro_rules! make_mir_visitor {
                             self.visit_operand(input, location);
                         }
                     }
+                    StatementKind::Retag { ref $($mutability)* fn_entry,
+                                           ref $($mutability)* place } => {
+                        self.visit_retag(fn_entry, place, location);
+                    }
                     StatementKind::AscribeUserType(
                         ref $($mutability)* place,
                         ref $($mutability)* variance,
@@ -719,6 +719,17 @@ macro_rules! make_mir_visitor {
                 self.visit_user_type_projection(user_ty);
             }
 
+            fn super_retag(&mut self,
+                           _fn_entry: & $($mutability)* bool,
+                           place: & $($mutability)* Place<'tcx>,
+                           location: Location) {
+                self.visit_place(
+                    place,
+                    PlaceContext::MutatingUse(MutatingUseContext::Retag),
+                    location,
+                );
+            }
+
             fn super_place(&mut self,
                             place: & $($mutability)* Place<'tcx>,
                             context: PlaceContext<'tcx>,
@@ -1010,6 +1021,8 @@ pub enum MutatingUseContext<'tcx> {
     ///     f(&mut x.y);
     ///
     Projection,
+    /// Retagging (updating the "Stacked Borrows" tag)
+    Retag,
 }
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
@@ -1020,8 +1033,6 @@ pub enum NonUseContext {
     StorageDead,
     /// User type annotation assertions for NLL.
     AscribeUserTy,
-    /// Validation command.
-    Validate,
 }
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]

src/librustc/session/config.rs

@@ -1282,9 +1282,8 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         "in addition to `.mir` files, create graphviz `.dot` files"),
     dump_mir_exclude_pass_number: bool = (false, parse_bool, [UNTRACKED],
         "if set, exclude the pass number when dumping MIR (used in tests)"),
-    mir_emit_validate: usize = (0, parse_uint, [TRACKED],
-        "emit Validate MIR statements, interpreted e.g. by miri (0: do not emit; 1: if function \
-         contains unsafe block, only validate arguments; 2: always emit full validation)"),
+    mir_emit_retag: bool = (false, parse_bool, [TRACKED],
+        "emit Retagging MIR statements, interpreted e.g. by miri; implies -Zmir-opt-level=0"),
     perf_stats: bool = (false, parse_bool, [UNTRACKED],
         "print some performance-related statistics"),
     hir_stats: bool = (false, parse_bool, [UNTRACKED],

src/librustc/ty/context.rs

@@ -1547,11 +1547,9 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
     }
 
     /// Should we emit EndRegion MIR statements? These are consumed by
-    /// MIR borrowck, but not when NLL is used. They are also consumed
-    /// by the validation stuff.
+    /// MIR borrowck, but not when NLL is used.
     pub fn emit_end_regions(self) -> bool {
         self.sess.opts.debugging_opts.emit_end_regions ||
-            self.sess.opts.debugging_opts.mir_emit_validate > 0 ||
             self.use_mir_borrowck()
     }
 

src/librustc_codegen_llvm/mir/analyze.rs

@@ -219,7 +219,8 @@ impl Visitor<'tcx> for LocalAnalyzer<'mir, 'a, 'll, 'tcx> {
                 self.assign(local, location);
             }
 
-            PlaceContext::NonUse(_) => {}
+            PlaceContext::NonUse(_) |
+            PlaceContext::MutatingUse(MutatingUseContext::Retag) => {}
 
             PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy) |
             PlaceContext::NonMutatingUse(NonMutatingUseContext::Move) => {

src/librustc_codegen_llvm/mir/statement.rs

@@ -109,7 +109,7 @@ impl FunctionCx<'a, 'll, 'tcx> {
             }
             mir::StatementKind::FakeRead(..) |
             mir::StatementKind::EndRegion(_) |
-            mir::StatementKind::Validate(..) |
+            mir::StatementKind::Retag { .. } |
             mir::StatementKind::AscribeUserType(..) |
             mir::StatementKind::Nop => bx,
         }

src/librustc_mir/borrow_check/mod.rs

@@ -600,9 +600,9 @@ impl<'cx, 'gcx, 'tcx> DataflowResultsConsumer<'cx, 'tcx> for MirBorrowckCtxt<'cx
             }
             StatementKind::Nop
             | StatementKind::AscribeUserType(..)
-            | StatementKind::Validate(..)
+            | StatementKind::Retag { .. }
             | StatementKind::StorageLive(..) => {
-                // `Nop`, `AscribeUserType`, `Validate`, and `StorageLive` are irrelevant
+                // `Nop`, `AscribeUserType`, `Retag`, and `StorageLive` are irrelevant
                 // to borrow check.
             }
             StatementKind::StorageDead(local) => {

src/librustc_mir/borrow_check/nll/invalidation.rs

@@ -136,9 +136,9 @@ impl<'cx, 'tcx, 'gcx> Visitor<'tcx> for InvalidationGenerator<'cx, 'tcx, 'gcx> {
             StatementKind::EndRegion(..) |
             StatementKind::Nop |
             StatementKind::AscribeUserType(..) |
-            StatementKind::Validate(..) |
+            StatementKind::Retag { .. } |
             StatementKind::StorageLive(..) => {
-                // `Nop`, `AscribeUserType`, `Validate`, and `StorageLive` are irrelevant
+                // `Nop`, `AscribeUserType`, `Retag`, and `StorageLive` are irrelevant
                 // to borrow check.
             }
             StatementKind::StorageDead(local) => {