rust-lang#27282: Add StatementKind::ReadForMatch to MIR.

(This is just the data structure changes and some boilerplate match
code that followed from it; the actual emission of these statements
comes in a follow-up commit.)

Author: pnkfelix

src/librustc/ich/impls_mir.rs

@@ -241,6 +241,9 @@ for mir::StatementKind<'gcx> {
                 place.hash_stable(hcx, hasher);
                 rvalue.hash_stable(hcx, hasher);
             }
+            mir::StatementKind::ReadForMatch(ref place) => {
+                place.hash_stable(hcx, hasher);
+            }
             mir::StatementKind::SetDiscriminant { ref place, variant_index } => {
                 place.hash_stable(hcx, hasher);
                 variant_index.hash_stable(hcx, hasher);

src/librustc/mir/mod.rs

@@ -1225,6 +1225,10 @@ pub enum StatementKind<'tcx> {
     /// Write the RHS Rvalue to the LHS Place.
     Assign(Place<'tcx>, Rvalue<'tcx>),
 
+    /// This represents all the reading that a pattern match may do
+    /// (e.g. inspecting constants and discriminant values).
+    ReadForMatch(Place<'tcx>),
+
     /// Write the discriminant for a variant to the enum Place.
     SetDiscriminant { place: Place<'tcx>, variant_index: usize },
 
@@ -1327,6 +1331,7 @@ impl<'tcx> Debug for Statement<'tcx> {
         use self::StatementKind::*;
         match self.kind {
             Assign(ref place, ref rv) => write!(fmt, "{:?} = {:?}", place, rv),
+            ReadForMatch(ref place) => write!(fmt, "ReadForMatch({:?})", 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),
@@ -2212,6 +2217,7 @@ BraceStructTypeFoldableImpl! {
 EnumTypeFoldableImpl! {
     impl<'tcx> TypeFoldable<'tcx> for StatementKind<'tcx> {
         (StatementKind::Assign)(a, b),
+        (StatementKind::ReadForMatch)(place),
         (StatementKind::SetDiscriminant) { place, variant_index },
         (StatementKind::StorageLive)(a),
         (StatementKind::StorageDead)(a),

src/librustc/mir/visit.rs

@@ -355,6 +355,11 @@ macro_rules! make_mir_visitor {
                                           ref $($mutability)* rvalue) => {
                         self.visit_assign(block, place, rvalue, location);
                     }
+                    StatementKind::ReadForMatch(ref $($mutability)* place) => {
+                        self.visit_place(place,
+                                         PlaceContext::Inspect,
+                                         location);
+                    }
                     StatementKind::EndRegion(_) => {}
                     StatementKind::Validate(_, ref $($mutability)* places) => {
                         for operand in places {

src/librustc_codegen_llvm/mir/statement.rs

@@ -82,6 +82,7 @@ impl<'a, 'tcx> FunctionCx<'a, 'tcx> {
                 asm::codegen_inline_asm(&bx, asm, outputs, input_vals);
                 bx
             }
+            mir::StatementKind::ReadForMatch(_) |
             mir::StatementKind::EndRegion(_) |
             mir::StatementKind::Validate(..) |
             mir::StatementKind::UserAssertTy(..) |

src/librustc_mir/borrow_check/mod.rs

@@ -423,6 +423,14 @@ impl<'cx, 'gcx, 'tcx> DataflowResultsConsumer<'cx, 'tcx> for MirBorrowckCtxt<'cx
                     flow_state,
                 );
             }
+            StatementKind::ReadForMatch(ref place) => {
+                self.access_place(ContextKind::ReadForMatch.new(location),
+                                  (place, span),
+                                  (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
+                                  LocalMutationIsAllowed::No,
+                                  flow_state,
+                                  );
+            }
             StatementKind::SetDiscriminant {
                 ref place,
                 variant_index: _,
@@ -2090,6 +2098,7 @@ enum ContextKind {
     CallDest,
     Assert,
     Yield,
+    ReadForMatch,
     StorageDead,
 }
 

src/librustc_mir/borrow_check/nll/invalidation.rs

@@ -93,6 +93,14 @@ impl<'cg, 'cx, 'tcx, 'gcx> Visitor<'tcx> for InvalidationGenerator<'cg, 'cx, 'tc
                     JustWrite
                 );
             }
+            StatementKind::ReadForMatch(ref place) => {
+                self.access_place(
+                    ContextKind::ReadForMatch.new(location),
+                    place,
+                    (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
+                    LocalMutationIsAllowed::No,
+                );
+            }
             StatementKind::SetDiscriminant {
                 ref place,
                 variant_index: _,

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

@@ -836,7 +836,8 @@ impl<'a, 'gcx, 'tcx> TypeChecker<'a, 'gcx, 'tcx> {
                     );
                 }
             }
-            StatementKind::StorageLive(_)
+            StatementKind::ReadForMatch(_)
+            | StatementKind::StorageLive(_)
             | StatementKind::StorageDead(_)
             | StatementKind::InlineAsm { .. }
             | StatementKind::EndRegion(_)

src/librustc_mir/dataflow/impls/borrows.rs

@@ -227,6 +227,7 @@ impl<'a, 'gcx, 'tcx> BitDenotation for Borrows<'a, 'gcx, 'tcx> {
                 }
             }
 
+            mir::StatementKind::ReadForMatch(..) |
             mir::StatementKind::SetDiscriminant { .. } |
             mir::StatementKind::StorageLive(..) |
             mir::StatementKind::Validate(..) |

src/librustc_mir/dataflow/move_paths/builder.rs

@@ -278,6 +278,9 @@ impl<'b, 'a, 'gcx, 'tcx> Gatherer<'b, 'a, 'gcx, 'tcx> {
                 }
                 self.gather_rvalue(rval);
             }
+            StatementKind::ReadForMatch(ref place) => {
+                self.create_move_path(place);
+            }
             StatementKind::InlineAsm { ref outputs, ref inputs, ref asm } => {
                 for (output, kind) in outputs.iter().zip(&asm.outputs) {
                     if !kind.is_indirect {

src/librustc_mir/interpret/step.rs

@@ -79,6 +79,11 @@ impl<'a, 'mir, 'tcx, M: Machine<'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M> {
                 self.deallocate_local(old_val)?;
             }
 
+            // FIXME: is there some dynamic semantics we should attach to
+            // these? Or am I correct in thinking that the inerpreter
+            // is solely intended for borrowck'ed code?
+            ReadForMatch(..) => {}
+
             // Validity checks.
             Validate(op, ref places) => {
                 for operand in places {

src/librustc_mir/transform/check_unsafety.rs

@@ -100,6 +100,7 @@ impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
         self.source_info = statement.source_info;
         match statement.kind {
             StatementKind::Assign(..) |
+            StatementKind::ReadForMatch(..) |
             StatementKind::SetDiscriminant { .. } |
             StatementKind::StorageLive(..) |
             StatementKind::StorageDead(..) |

src/librustc_mir/transform/qualify_consts.rs

@@ -1135,6 +1135,7 @@ This does not pose a problem by itself because they can't be accessed directly."
                 StatementKind::Assign(ref place, ref rvalue) => {
                     this.visit_assign(bb, place, rvalue, location);
                 }
+                StatementKind::ReadForMatch(..) |
                 StatementKind::SetDiscriminant { .. } |
                 StatementKind::StorageLive(_) |
                 StatementKind::StorageDead(_) |

src/librustc_mir/transform/remove_noop_landing_pads.rs

@@ -47,6 +47,7 @@ impl RemoveNoopLandingPads {
     {
         for stmt in &mir[bb].statements {
             match stmt.kind {
+                StatementKind::ReadForMatch(_) |
                 StatementKind::StorageLive(_) |
                 StatementKind::StorageDead(_) |
                 StatementKind::EndRegion(_) |

src/librustc_mir/transform/rustc_peek.rs

@@ -158,6 +158,7 @@ fn each_block<'a, 'tcx, O>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
             mir::StatementKind::Assign(ref place, ref rvalue) => {
                 (place, rvalue)
             }
+            mir::StatementKind::ReadForMatch(_) |
             mir::StatementKind::StorageLive(_) |
             mir::StatementKind::StorageDead(_) |
             mir::StatementKind::InlineAsm { .. } |

src/librustc_passes/mir_stats.rs

@@ -85,6 +85,7 @@ impl<'a, 'tcx> mir_visit::Visitor<'tcx> for StatCollector<'a, 'tcx> {
         self.record("Statement", statement);
         self.record(match statement.kind {
             StatementKind::Assign(..) => "StatementKind::Assign",
+            StatementKind::ReadForMatch(..) => "StatementKind::ReadForMatch",
             StatementKind::EndRegion(..) => "StatementKind::EndRegion",
             StatementKind::Validate(..) => "StatementKind::Validate",
             StatementKind::SetDiscriminant { .. } => "StatementKind::SetDiscriminant",