Use normal mutable borrows in MIR match lowering

Author: matthewjasper

src/librustc/ich/impls_mir.rs

@@ -196,7 +196,12 @@ impl_stable_hash_for!(impl<'gcx> for enum mir::StatementKind<'gcx> [ mir::Statem
 });
 
 impl_stable_hash_for!(enum mir::RetagKind { FnEntry, TwoPhase, Raw, Default });
-impl_stable_hash_for!(enum mir::FakeReadCause { ForMatchGuard, ForMatchedPlace, ForLet });
+impl_stable_hash_for!(enum mir::FakeReadCause {
+    ForMatchGuard,
+    ForMatchedPlace,
+    ForGuardBinding,
+    ForLet
+});
 
 impl<'a, 'gcx> HashStable<StableHashingContext<'a>> for mir::Place<'gcx> {
     fn hash_stable<W: StableHasherResult>(&self,

src/librustc/mir/mod.rs

@@ -1823,17 +1823,22 @@ pub enum RetagKind {
 /// The `FakeReadCause` describes the type of pattern why a `FakeRead` statement exists.
 #[derive(Copy, Clone, RustcEncodable, RustcDecodable, Debug)]
 pub enum FakeReadCause {
-    /// Inject a fake read of the borrowed input at the start of each arm's
-    /// pattern testing code.
+    /// Inject a fake read of the borrowed input at the end of each guards
+    /// code.
     ///
-    /// This should ensure that you cannot change the variant for an enum
-    /// while you are in the midst of matching on it.
+    /// This should ensure that you cannot change the variant for an enum while
+    /// you are in the midst of matching on it.
     ForMatchGuard,
 
     /// `let x: !; match x {}` doesn't generate any read of x so we need to
     /// generate a read of x to check that it is initialized and safe.
     ForMatchedPlace,
 
+    /// A fake read of the RefWithinGuard version of a bind-by-value variable
+    /// in a match guard to ensure that it's value hasn't change by the time
+    /// we create the OutsideGuard version.
+    ForGuardBinding,
+
     /// Officially, the semantics of
     ///
     /// `let pattern = <expr>;`

src/librustc_mir/borrow_check/mod.rs

@@ -998,7 +998,9 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
                 }
 
                 (Read(_), BorrowKind::Shared) | (Reservation(..), BorrowKind::Shared)
-                | (Read(_), BorrowKind::Shallow) | (Reservation(..), BorrowKind::Shallow) => {
+                | (Read(_), BorrowKind::Shallow) | (Reservation(..), BorrowKind::Shallow)
+                | (Read(ReadKind::Borrow(BorrowKind::Shallow)), BorrowKind::Unique)
+                | (Read(ReadKind::Borrow(BorrowKind::Shallow)), BorrowKind::Mut { .. }) => {
                     Control::Continue
                 }
 

src/librustc_mir/borrow_check/nll/invalidation.rs

@@ -78,13 +78,8 @@ impl<'cx, 'tcx, 'gcx> Visitor<'tcx> for InvalidationGenerator<'cx, 'tcx, 'gcx> {
                     JustWrite
                 );
             }
-            StatementKind::FakeRead(_, ref place) => {
-                self.access_place(
-                    ContextKind::FakeRead.new(location),
-                    place,
-                    (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
-                    LocalMutationIsAllowed::No,
-                );
+            StatementKind::FakeRead(_, _) => {
+                // Only relavent for initialized/liveness/safety checks.
             }
             StatementKind::SetDiscriminant {
                 ref place,
@@ -438,7 +433,9 @@ impl<'cg, 'cx, 'tcx, 'gcx> InvalidationGenerator<'cx, 'tcx, 'gcx> {
                     }
 
                     (Read(_), BorrowKind::Shallow) | (Reservation(..), BorrowKind::Shallow)
-                    | (Read(_), BorrowKind::Shared) | (Reservation(..), BorrowKind::Shared) => {
+                    | (Read(_), BorrowKind::Shared) | (Reservation(..), BorrowKind::Shared)
+                    | (Read(ReadKind::Borrow(BorrowKind::Shallow)), BorrowKind::Unique)
+                    | (Read(ReadKind::Borrow(BorrowKind::Shallow)), BorrowKind::Mut { .. }) => {
                         // Reads/reservations don't invalidate shared or shallow borrows
                     }
 

src/librustc_mir/build/block.rs

@@ -6,8 +6,6 @@ use rustc::mir::*;
 use rustc::hir;
 use syntax_pos::Span;
 
-use std::slice;
-
 impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
     pub fn ast_block(&mut self,
                      destination: &Place<'tcx>,
@@ -125,7 +123,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                             None,
                             remainder_span,
                             lint_level,
-                            slice::from_ref(&pattern),
+                            &pattern,
                             ArmHasGuard(false),
                             Some((None, initializer_span)),
                         );
@@ -138,7 +136,7 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                             }));
                     } else {
                         scope = this.declare_bindings(
-                            None, remainder_span, lint_level, slice::from_ref(&pattern),
+                            None, remainder_span, lint_level, &pattern,
                             ArmHasGuard(false), None);
 
                         debug!("ast_block_stmts: pattern={:?}", pattern);