Remove cat_discr

it seems to be some kind of GC-related mess

src/librustc/middle/borrowck/check_loans.rs

@@ -831,7 +831,6 @@ impl<'a, 'tcx> CheckLoanCtxt<'a, 'tcx> {
                         return;
                     }
 
-                    mc::cat_discr(b, _) |
                     mc::cat_deref(b, _, mc::OwnedPtr) => {
                         assert_eq!(cmt.mutbl, mc::McInherited);
                         cmt = b;

src/librustc/middle/borrowck/gather_loans/gather_moves.rs

@@ -159,8 +159,7 @@ fn check_and_get_illegal_move_origin(bccx: &BorrowckCtxt,
             }
         }
 
-        mc::cat_deref(ref b, _, mc::OwnedPtr) |
-        mc::cat_discr(ref b, _) => {
+        mc::cat_deref(ref b, _, mc::OwnedPtr) => {
             check_and_get_illegal_move_origin(bccx, b)
         }
     }

src/librustc/middle/borrowck/gather_loans/lifetime.rs

@@ -84,62 +84,6 @@ impl<'a, 'tcx> GuaranteeLifetimeContext<'a, 'tcx> {
             mc::cat_interior(ref base, _) => {             // L-Field
                 self.check(base, discr_scope)
             }
-
-            mc::cat_discr(ref base, new_discr_scope) => {
-                // Subtle: in a match, we must ensure that each binding
-                // variable remains valid for the duration of the arm in
-                // which it appears, presuming that this arm is taken.
-                // But it is inconvenient in trans to root something just
-                // for one arm.  Therefore, we insert a cat_discr(),
-                // basically a special kind of category that says "if this
-                // value must be dynamically rooted, root it for the scope
-                // `match_id`".
-                //
-                // As an example, consider this scenario:
-                //
-                //    let mut x = @Some(3);
-                //    match *x { Some(y) {...} None {...} }
-                //
-                // Technically, the value `x` need only be rooted
-                // in the `some` arm.  However, we evaluate `x` in trans
-                // before we know what arm will be taken, so we just
-                // always root it for the duration of the match.
-                //
-                // As a second example, consider *this* scenario:
-                //
-                //    let x = @@Some(3);
-                //    match x { @@Some(y) {...} @@None {...} }
-                //
-                // Here again, `x` need only be rooted in the `some` arm.
-                // In this case, the value which needs to be rooted is
-                // found only when checking which pattern matches: but
-                // this check is done before entering the arm.  Therefore,
-                // even in this case we just choose to keep the value
-                // rooted for the entire match.  This means the value will be
-                // rooted even if the none arm is taken.  Oh well.
-                //
-                // At first, I tried to optimize the second case to only
-                // root in one arm, but the result was suboptimal: first,
-                // it interfered with the construction of phi nodes in the
-                // arm, as we were adding code to root values before the
-                // phi nodes were added.  This could have been addressed
-                // with a second basic block.  However, the naive approach
-                // also yielded suboptimal results for patterns like:
-                //
-                //    let x = @@...;
-                //    match x { @@some_variant(y) | @@some_other_variant(y) =>
-                //
-                // The reason is that we would root the value once for
-                // each pattern and not once per arm.  This is also easily
-                // fixed, but it's yet more code for what is really quite
-                // the corner case.
-                //
-                // Nonetheless, if you decide to optimize this case in the
-                // future, you need only adjust where the cat_discr()
-                // node appears to draw the line between what will be rooted
-                // in the *arm* vs the *match*.
-                self.check(base, Some(new_discr_scope))
-            }
         }
     }
 
@@ -182,8 +126,7 @@ impl<'a, 'tcx> GuaranteeLifetimeContext<'a, 'tcx> {
             }
             mc::cat_downcast(ref cmt) |
             mc::cat_deref(ref cmt, _, mc::OwnedPtr) |
-            mc::cat_interior(ref cmt, _) |
-            mc::cat_discr(ref cmt, _) => {
+            mc::cat_interior(ref cmt, _) => {
                 self.scope(cmt)
             }
         }

src/librustc/middle/borrowck/gather_loans/mod.rs

@@ -213,9 +213,7 @@ impl<'a, 'tcx> GatherLoanCtxt<'a, 'tcx> {
         /*!
          * Guarantees that `addr_of(cmt)` will be valid for the duration of
          * `static_scope_r`, or reports an error.  This may entail taking
-         * out loans, which will be added to the `req_loan_map`.  This can
-         * also entail "rooting" GC'd pointers, which means ensuring
-         * dynamically that they are not freed.
+         * out loans, which will be added to the `req_loan_map`.
          */
 
         debug!("guarantee_valid(borrow_id={}, cmt={}, \

src/librustc/middle/borrowck/gather_loans/restrictions.rs

@@ -96,46 +96,27 @@ impl<'a, 'tcx> RestrictionsContext<'a, 'tcx> {
                 self.extend(result, cmt.mutbl, LpInterior(i))
             }
 
-            mc::cat_deref(cmt_base, _, pk @ mc::OwnedPtr) => {
-                // R-Deref-Send-Pointer
-                //
-                // When we borrow the interior of an owned pointer, we
-                // cannot permit the base to be mutated, because that
-                // would cause the unique pointer to be freed.
-                //
-                // Eventually we should make these non-special and
-                // just rely on Deref<T> implementation.
-                let result = self.restrict(cmt_base);
-                self.extend(result, cmt.mutbl, LpDeref(pk))
-            }
 
             mc::cat_static_item(..) => {
                 Safe
             }
 
-            mc::cat_deref(cmt_base, _, mc::BorrowedPtr(ty::ImmBorrow, lt)) |
-            mc::cat_deref(cmt_base, _, mc::Implicit(ty::ImmBorrow, lt)) => {
-                // R-Deref-Imm-Borrowed
-                if !self.bccx.is_subregion_of(self.loan_region, lt) {
-                    self.bccx.report(
-                        BckError {
-                            span: self.span,
-                            cause: self.cause,
-                            cmt: cmt_base,
-                            code: err_borrowed_pointer_too_short(
-                                self.loan_region, lt)});
-                    return Safe;
-                }
-                Safe
-            }
-
             mc::cat_deref(cmt_base, _, pk) => {
                 match pk {
-                    mc::BorrowedPtr(ty::MutBorrow, lt) |
-                    mc::BorrowedPtr(ty::UniqueImmBorrow, lt) |
-                    mc::Implicit(ty::MutBorrow, lt) |
-                    mc::Implicit(ty::UniqueImmBorrow, lt) => {
-                        // R-Deref-Mut-Borrowed
+                    mc::OwnedPtr => {
+                        // R-Deref-Send-Pointer
+                        //
+                        // When we borrow the interior of an owned pointer, we
+                        // cannot permit the base to be mutated, because that
+                        // would cause the unique pointer to be freed.
+                        //
+                        // Eventually we should make these non-special and
+                        // just rely on Deref<T> implementation.
+                        let result = self.restrict(cmt_base);
+                        self.extend(result, cmt.mutbl, LpDeref(pk))
+                    }
+                    mc::Implicit(bk, lt) | mc::BorrowedPtr(bk, lt) => {
+                        // R-Deref-[Mut-]Borrowed
                         if !self.bccx.is_subregion_of(self.loan_region, lt) {
                             self.bccx.report(
                                 BckError {
@@ -147,25 +128,23 @@ impl<'a, 'tcx> RestrictionsContext<'a, 'tcx> {
                             return Safe;
                         }
 
-                        let result = self.restrict(cmt_base);
-                        self.extend(result, cmt.mutbl, LpDeref(pk))
-                    }
-                    mc::UnsafePtr(..) => {
-                        // We are very trusting when working with unsafe
-                        // pointers.
-                        Safe
-                    }
-                    _ => {
-                        self.bccx.tcx.sess.span_bug(self.span,
-                                                    "unhandled memcat in \
-                                                     cat_deref")
+                        match bk {
+                            ty::ImmBorrow => Safe,
+                            ty::MutBorrow | ty::UniqueImmBorrow => {
+                                // R-Deref-Mut-Borrowed
+                                //
+                                // The referent can be aliased after the
+                                // references lifetime ends (by a newly-unfrozen
+                                // borrow).
+                                let result = self.restrict(cmt_base);
+                                self.extend(result, cmt.mutbl, LpDeref(pk))
+                            }
+                        }
                     }
+                    // Borrowck is not relevant for unsafe pointers
+                    mc::UnsafePtr(..) => Safe
                 }
             }
-
-            mc::cat_discr(cmt_base, _) => {
-                self.restrict(cmt_base)
-            }
         }
     }
 

src/librustc/middle/borrowck/mod.rs

@@ -379,8 +379,7 @@ pub fn opt_loan_path(cmt: &mc::cmt) -> Option<Rc<LoanPath>> {
             })
         }
 
-        mc::cat_downcast(ref cmt_base) |
-        mc::cat_discr(ref cmt_base, _) => {
+        mc::cat_downcast(ref cmt_base) => {
             opt_loan_path(cmt_base)
         }
     }

src/librustc/middle/check_static.rs

@@ -269,7 +269,6 @@ impl euv::Delegate for GlobalChecker {
                     break
                 }
                 mc::cat_deref(ref cmt, _, _) |
-                mc::cat_discr(ref cmt, _) |
                 mc::cat_downcast(ref cmt) |
                 mc::cat_interior(ref cmt, _) => cur = cmt,
 
@@ -307,7 +306,6 @@ impl euv::Delegate for GlobalChecker {
                 }
 
                 mc::cat_downcast(..) |
-                mc::cat_discr(..) |
                 mc::cat_upvar(..) => unreachable!(),
 
                 mc::cat_local(..) => {
@@ -331,4 +329,3 @@ impl euv::Delegate for GlobalChecker {
                    _cmt: mc::cmt,
                    _mode: euv::ConsumeMode) {}
 }
-

src/librustc/middle/mem_categorization.rs

@@ -87,7 +87,6 @@ pub enum categorization {
     cat_deref(cmt, uint, PointerKind), // deref of a ptr
     cat_interior(cmt, InteriorKind),   // something interior: field, tuple, etc
     cat_downcast(cmt),                 // selects a particular enum variant (*1)
-    cat_discr(cmt, ast::NodeId),       // match discriminant (see preserve())
 
     // (*1) downcast is only required if the enum has more than one variant
 }
@@ -1339,9 +1338,6 @@ impl<'t,'tcx,TYPER:Typer<'tcx>> MemCategorizationContext<'t,TYPER> {
           cat_upvar(ref var) => {
               upvar_to_string(var, true)
           }
-          cat_discr(ref cmt, _) => {
-            self.cmt_to_string(&**cmt)
-          }
           cat_downcast(ref cmt) => {
             self.cmt_to_string(&**cmt)
           }
@@ -1379,7 +1375,6 @@ impl cmt_ {
                 Rc::new((*self).clone())
             }
             cat_downcast(ref b) |
-            cat_discr(ref b, _) |
             cat_interior(ref b, _) |
             cat_deref(ref b, _, OwnedPtr) => {
                 b.guarantor()
@@ -1404,8 +1399,7 @@ impl cmt_ {
             cat_deref(ref b, _, Implicit(ty::UniqueImmBorrow, _)) |
             cat_downcast(ref b) |
             cat_deref(ref b, _, OwnedPtr) |
-            cat_interior(ref b, _) |
-            cat_discr(ref b, _) => {
+            cat_interior(ref b, _) => {
                 // Aliasability depends on base cmt
                 b.freely_aliasable(ctxt)
             }
@@ -1490,9 +1484,6 @@ impl Repr for categorization {
             cat_downcast(ref cmt) => {
                 format!("{}->(enum)", cmt.cat.repr(tcx))
             }
-            cat_discr(ref cmt, _) => {
-                cmt.cat.repr(tcx)
-            }
         }
     }
 }

src/librustc/middle/typeck/check/regionck.rs

@@ -1494,7 +1494,6 @@ fn link_region(rcx: &Rcx,
                 }
             }
 
-            mc::cat_discr(cmt_base, _) |
             mc::cat_downcast(cmt_base) |
             mc::cat_deref(cmt_base, _, mc::OwnedPtr) |
             mc::cat_interior(cmt_base, _) => {
@@ -1736,8 +1735,7 @@ fn adjust_upvar_borrow_kind_for_mut(rcx: &Rcx,
         match cmt.cat.clone() {
             mc::cat_deref(base, _, mc::OwnedPtr) |
             mc::cat_interior(base, _) |
-            mc::cat_downcast(base) |
-            mc::cat_discr(base, _) => {
+            mc::cat_downcast(base) => {
                 // Interior or owned data is mutable if base is
                 // mutable, so iterate to the base.
                 cmt = base;
@@ -1788,8 +1786,7 @@ fn adjust_upvar_borrow_kind_for_unique(rcx: &Rcx, cmt: mc::cmt) {
         match cmt.cat.clone() {
             mc::cat_deref(base, _, mc::OwnedPtr) |
             mc::cat_interior(base, _) |
-            mc::cat_downcast(base) |
-            mc::cat_discr(base, _) => {
+            mc::cat_downcast(base) => {
                 // Interior or owned data is unique if base is
                 // unique.
                 cmt = base;