Initial implementation of enum discrimnant sizing.

Allows an enum with a discriminant to use any of the primitive integer
types to store it.  By default the smallest usable type is chosen, but
this can be overridden with an attribute: `#[repr(int)]` etc., or
`#[repr(C)]` to match the target's C ABI for the equivalent C enum.

This commit breaks a few things, due to transmutes that now no longer
match in size, or u8 enums being passed to C that expects int, or
reflection; later commits on this branch fix them.

src/librustc/middle/trans/adt.rs

@@ -14,7 +14,8 @@
  * This module determines how to represent enums, structs, and tuples
  * based on their monomorphized types; it is responsible both for
  * choosing a representation and translating basic operations on
- * values of those types.
+ * values of those types.  (Note: exporting the representations for
+ * debuggers is handled in debuginfo.rs, not here.)
  *
  * Note that the interface treats everything as a general case of an
  * enum, so structs/tuples/etc. have one pseudo-variant with
@@ -29,8 +30,6 @@
  *   that might contain one and adjust GEP indices accordingly.  See
  *   issue #4578.
  *
- * - Using smaller integer types for discriminants.
- *
  * - Store nested enums' discriminants in the same word.  Rather, if
  *   some variants start with enums, and those enums representations
  *   have unused alignment padding between discriminant and body, the
@@ -56,16 +55,21 @@ use middle::trans::machine;
 use middle::trans::type_of;
 use middle::ty;
 use middle::ty::Disr;
+use syntax::abi::{X86, X86_64, Arm, Mips};
 use syntax::ast;
+use syntax::attr;
+use syntax::attr::IntType;
 use util::ppaux::ty_to_str;
 
 use middle::trans::type_::Type;
 
+type Hint = attr::ReprAttr;
+
 
 /// Representations.
 pub enum Repr {
     /// C-like enums; basically an int.
-    CEnum(Disr, Disr), // discriminant range
+    CEnum(IntType, Disr, Disr), // discriminant range (signedness based on the IntType)
     /**
      * Single-case variants, and structs/tuples/records.
      *
@@ -78,7 +82,7 @@ pub enum Repr {
      * General-case enums: for each case there is a struct, and they
      * all start with a field for the discriminant.
      */
-    General(~[Struct]),
+    General(IntType, ~[Struct]),
     /**
      * Two cases distinguished by a nullable pointer: the case with discriminant
      * `nndiscr` is represented by the struct `nonnull`, where the `ptrfield`th
@@ -166,11 +170,19 @@ fn represent_type_uncached(cx: &mut CrateContext, t: ty::t) -> Repr {
             if cases.iter().all(|c| c.tys.len() == 0) {
                 // All bodies empty -> intlike
                 let discrs = cases.map(|c| c.discr);
-                return CEnum(*discrs.iter().min().unwrap(), *discrs.iter().max().unwrap());
+                let hint = ty::lookup_repr_hint(cx.tcx, def_id);
+                let bounds = IntBounds {
+                    ulo: *discrs.iter().min().unwrap(),
+                    uhi: *discrs.iter().max().unwrap(),
+                    slo: discrs.iter().map(|n| *n as i64).min().unwrap(),
+                    shi: discrs.iter().map(|n| *n as i64).max().unwrap()
+                };
+                return mk_cenum(cx, hint, &bounds);
             }
 
             if cases.len() == 1 {
                 // Equivalent to a struct/tuple/newtype.
+                // FIXME: should this conflict with a discriminant size hint?
                 assert_eq!(cases[0].discr, 0);
                 return Univariant(mk_struct(cx, cases[0].tys, false), false)
             }
@@ -185,6 +197,7 @@ fn represent_type_uncached(cx: &mut CrateContext, t: ty::t) -> Repr {
             }
 
             if cases.len() == 2 {
+                // FIXME: disable if size hint present?
                 let mut discr = 0;
                 while discr < 2 {
                     if cases[1 - discr].is_zerolen(cx) {
@@ -207,8 +220,13 @@ fn represent_type_uncached(cx: &mut CrateContext, t: ty::t) -> Repr {
             }
 
             // The general case.
-            let discr = ~[ty::mk_uint()];
+            let hint = ty::lookup_repr_hint(cx.tcx, def_id);
-            return General(cases.map(|c| mk_struct(cx, discr + c.tys, false)))
+            assert!((cases.len() - 1) as i64 >= 0);
+            let bounds = IntBounds { ulo: 0, uhi: (cases.len() - 1) as u64,
+                                     slo: 0, shi: (cases.len() - 1) as i64 };
+            let ity = range_to_inttype(cx, hint, &bounds);
+            let discr = ~[ty_of_inttype(ity)];
+            return General(ity, cases.map(|c| mk_struct(cx, discr + c.tys, false)))
         }
         _ => cx.sess.bug("adt::represent_type called on non-ADT type")
     }
@@ -225,6 +243,93 @@ fn mk_struct(cx: &mut CrateContext, tys: &[ty::t], packed: bool) -> Struct {
     }
 }
 
+struct IntBounds {
+    slo: i64,
+    shi: i64,
+    ulo: u64,
+    uhi: u64
+}
+
+fn mk_cenum(cx: &mut CrateContext, hint: Hint, bounds: &IntBounds) -> Repr {
+    let it = range_to_inttype(cx, hint, bounds);
+    match it {
+        attr::SignedInt(_) => CEnum(it, bounds.slo as Disr, bounds.shi as Disr),
+        attr::UnsignedInt(_) => CEnum(it, bounds.ulo, bounds.uhi)
+    }
+}
+
+fn range_to_inttype(cx: &mut CrateContext, hint: Hint, bounds: &IntBounds) -> IntType {
+    debug!("range_to_inttype: {:?} {:?}", hint, bounds);
+    // Lists of sizes to try.  u64 is always allowed as a fallback.
+    static choose_shortest: &'static[IntType] = &[
+        attr::UnsignedInt(ast::ty_u8), attr::SignedInt(ast::ty_i8),
+        attr::UnsignedInt(ast::ty_u16), attr::SignedInt(ast::ty_i16),
+        attr::UnsignedInt(ast::ty_u32), attr::SignedInt(ast::ty_i32)];
+    static at_least_32: &'static[IntType] = &[
+        attr::UnsignedInt(ast::ty_u32), attr::SignedInt(ast::ty_i32)];
+
+    let attempts;
+    match hint {
+        attr::ReprInt(span, ity) => {
+            if !bounds_usable(cx, ity, bounds) {
+                cx.sess.span_err(span, "representation hint insufficient for discriminant range")
+            }
+            return ity;
+        }
+        attr::ReprExtern => {
+            attempts = match cx.sess.targ_cfg.arch {
+                X86 | X86_64 => at_least_32,
+                // WARNING: the ARM EABI has two variants; the one corresponding to `at_least_32`
+                // appears to be used on Linux and NetBSD, but some systems may use the variant
+                // corresponding to `choose_shortest`.  However, we don't run on those yet...?
+                Arm => at_least_32,
+                Mips => at_least_32,
+            }
+        }
+        attr::ReprAny => {
+            attempts = choose_shortest;
+        }
+    }
+    let mut best = attr::UnsignedInt(ast::ty_u64);
+    for &ity in attempts.iter() {
+        if bounds_usable(cx, ity, bounds) {
+            best = ity;
+            break;
+        }
+    }
+    return best;
+}
+
+pub fn ll_inttype(cx: &mut CrateContext, ity: IntType) -> Type {
+    match ity {
+        attr::SignedInt(t) => Type::int_from_ty(cx, t),
+        attr::UnsignedInt(t) => Type::uint_from_ty(cx, t)
+    }
+}
+
+fn bounds_usable(cx: &mut CrateContext, ity: IntType, bounds: &IntBounds) -> bool {
+    debug!("bounds_usable: {:?} {:?}", ity, bounds);
+    match ity {
+        attr::SignedInt(_) => {
+            let lllo = C_integral(ll_inttype(cx, ity), bounds.slo as u64, true);
+            let llhi = C_integral(ll_inttype(cx, ity), bounds.shi as u64, true);
+            bounds.slo == const_to_int(lllo) as i64 && bounds.shi == const_to_int(llhi) as i64
+        }
+        attr::UnsignedInt(_) => {
+            let lllo = C_integral(ll_inttype(cx, ity), bounds.ulo, false);
+            let llhi = C_integral(ll_inttype(cx, ity), bounds.uhi, false);
+            bounds.ulo == const_to_uint(lllo) as u64 && bounds.uhi == const_to_uint(llhi) as u64
+        }
+    }
+}
+
+fn ty_of_inttype(ity: IntType) -> ty::t {
+    match ity {
+        attr::SignedInt(t) => ty::mk_mach_int(t),
+        attr::UnsignedInt(t) => ty::mk_mach_uint(t)
+    }
+}
+
 /**
  * Returns the fields of a struct for the given representation.
  * All nominal types are LLVM structs, in order to be able to use
@@ -239,10 +344,10 @@ pub fn sizing_fields_of(cx: &mut CrateContext, r: &Repr) -> ~[Type] {
 }
 fn generic_fields_of(cx: &mut CrateContext, r: &Repr, sizing: bool) -> ~[Type] {
     match *r {
-        CEnum(*) => ~[Type::enum_discrim(cx)],
+        CEnum(ity, _, _) => ~[ll_inttype(cx, ity)],
         Univariant(ref st, _dtor) => struct_llfields(cx, st, sizing),
         NullablePointer{ nonnull: ref st, _ } => struct_llfields(cx, st, sizing),
-        General(ref sts) => {
+        General(_ity, ref sts) => {
             // To get "the" type of a general enum, we pick the case
             // with the largest alignment (so it will always align
             // correctly in containing structures) and pad it out.
@@ -288,7 +393,7 @@ pub fn trans_switch(bcx: @mut Block, r: &Repr, scrutinee: ValueRef)
     -> (_match::branch_kind, Option<ValueRef>) {
     match *r {
         CEnum(*) | General(*) => {
-            (_match::switch, Some(trans_get_discr(bcx, r, scrutinee)))
+            (_match::switch, Some(trans_get_discr(bcx, r, scrutinee, None)))
         }
         NullablePointer{ nonnull: ref nonnull, nndiscr, ptrfield, _ } => {
             (_match::switch, Some(nullable_bitdiscr(bcx, nonnull, nndiscr, ptrfield, scrutinee)))
@@ -302,16 +407,31 @@ pub fn trans_switch(bcx: @mut Block, r: &Repr, scrutinee: ValueRef)
 
 
 /// Obtain the actual discriminant of a value.
-pub fn trans_get_discr(bcx: @mut Block, r: &Repr, scrutinee: ValueRef)
+pub fn trans_get_discr(bcx: @mut Block, r: &Repr, scrutinee: ValueRef, cast_to: Option<Type>)
     -> ValueRef {
+    let signed;
+    let val;
     match *r {
-        CEnum(min, max) => load_discr(bcx, scrutinee, min, max),
+        CEnum(ity, min, max) => {
-        Univariant(*) => C_disr(bcx.ccx(), 0),
+            val = load_discr(bcx, ity, scrutinee, min, max);
-        General(ref cases) => load_discr(bcx, scrutinee, 0, (cases.len() - 1) as Disr),
+            signed = ity.is_signed();
-        NullablePointer{ nonnull: ref nonnull, nndiscr, ptrfield, _ } => {
-            ZExt(bcx, nullable_bitdiscr(bcx, nonnull, nndiscr, ptrfield, scrutinee),
-                 Type::enum_discrim(bcx.ccx()))
         }
+        General(ity, ref cases) => {
+            val = load_discr(bcx, ity, scrutinee, 0, (cases.len() - 1) as Disr);
+            signed = ity.is_signed();
+        }
+        Univariant(*) => {
+            val = C_u8(0);
+            signed = false;
+        }
+        NullablePointer{ nonnull: ref nonnull, nndiscr, ptrfield, _ } => {
+            val = nullable_bitdiscr(bcx, nonnull, nndiscr, ptrfield, scrutinee);
+            signed = false;
+        }
+    }
+    match cast_to {
+        None => val,
+        Some(llty) => if signed { SExt(bcx, val, llty) } else { ZExt(bcx, val, llty) }
     }
 }
 
@@ -324,10 +444,15 @@ fn nullable_bitdiscr(bcx: @mut Block, nonnull: &Struct, nndiscr: Disr, ptrfield:
 }
 
 /// Helper for cases where the discriminant is simply loaded.
-fn load_discr(bcx: @mut Block, scrutinee: ValueRef, min: Disr, max: Disr)
+fn load_discr(bcx: @mut Block, ity: IntType, scrutinee: ValueRef, min: Disr, max: Disr)
     -> ValueRef {
     let ptr = GEPi(bcx, scrutinee, [0, 0]);
-    if max + 1 == min {
+    let llty = ll_inttype(bcx.ccx(), ity);
+    assert_eq!(val_ty(ptr), llty.ptr_to());
+    let bits = machine::llbitsize_of_real(bcx.ccx(), llty);
+    assert!(bits <= 64);
+    let mask = (-1u64 >> (64 - bits)) as Disr;
+    if (max + 1) & mask == min & mask {
         // i.e., if the range is everything.  The lo==hi case would be
         // rejected by the LLVM verifier (it would mean either an
         // empty set, which is impossible, or the entire range of the
@@ -350,15 +475,17 @@ fn load_discr(bcx: @mut Block, scrutinee: ValueRef, min: Disr, max: Disr)
  */
 pub fn trans_case(bcx: @mut Block, r: &Repr, discr: Disr) -> _match::opt_result {
     match *r {
-        CEnum(*) => {
+        CEnum(ity, _, _) => {
-            _match::single_result(rslt(bcx, C_disr(bcx.ccx(), discr)))
+            _match::single_result(rslt(bcx, C_integral(ll_inttype(bcx.ccx(), ity),
+                                                       discr as u64, true)))
+        }
+        General(ity, _) => {
+            _match::single_result(rslt(bcx, C_integral(ll_inttype(bcx.ccx(), ity),
+                                                       discr as u64, true)))
         }
         Univariant(*) => {
             bcx.ccx().sess.bug("no cases for univariants or structs")
         }
-        General(*) => {
-            _match::single_result(rslt(bcx, C_disr(bcx.ccx(), discr)))
-        }
         NullablePointer{ _ } => {
             assert!(discr == 0 || discr == 1);
             _match::single_result(rslt(bcx, C_i1(discr != 0)))
@@ -373,9 +500,14 @@ pub fn trans_case(bcx: @mut Block, r: &Repr, discr: Disr) -> _match::opt_result
  */
 pub fn trans_start_init(bcx: @mut Block, r: &Repr, val: ValueRef, discr: Disr) {
     match *r {
-        CEnum(min, max) => {
+        CEnum(ity, min, max) => {
-            assert!(min <= discr && discr <= max);
+            assert_discr_in_range(ity, min, max, discr);
-            Store(bcx, C_disr(bcx.ccx(), discr), GEPi(bcx, val, [0, 0]))
+            Store(bcx, C_integral(ll_inttype(bcx.ccx(), ity), discr as u64, true),
+                  GEPi(bcx, val, [0, 0]))
+        }
+        General(ity, _) => {
+            Store(bcx, C_integral(ll_inttype(bcx.ccx(), ity), discr as u64, true),
+                  GEPi(bcx, val, [0, 0]))
         }
         Univariant(ref st, true) => {
             assert_eq!(discr, 0);
@@ -385,9 +517,6 @@ pub fn trans_start_init(bcx: @mut Block, r: &Repr, val: ValueRef, discr: Disr) {
         Univariant(*) => {
             assert_eq!(discr, 0);
         }
-        General(*) => {
-            Store(bcx, C_disr(bcx.ccx(), discr), GEPi(bcx, val, [0, 0]))
-        }
         NullablePointer{ nonnull: ref nonnull, nndiscr, ptrfield, _ } => {
             if discr != nndiscr {
                 let llptrptr = GEPi(bcx, val, [0, ptrfield]);
@@ -398,6 +527,13 @@ pub fn trans_start_init(bcx: @mut Block, r: &Repr, val: ValueRef, discr: Disr) {
     }
 }
 
+fn assert_discr_in_range(ity: IntType, min: Disr, max: Disr, discr: Disr) {
+    match ity {
+        attr::UnsignedInt(_) => assert!(min <= discr && discr <= max),
+        attr::SignedInt(_) => assert!(min as i64 <= discr as i64 && discr as i64 <= max as i64)
+    }
+}
+
 /**
  * The number of fields in a given case; for use when obtaining this
  * information from the type or definition is less convenient.
@@ -409,7 +545,7 @@ pub fn num_args(r: &Repr, discr: Disr) -> uint {
             assert_eq!(discr, 0);
             st.fields.len() - (if dtor { 1 } else { 0 })
         }
-        General(ref cases) => cases[discr].fields.len() - 1,
+        General(_, ref cases) => cases[discr].fields.len() - 1,
         NullablePointer{ nonnull: ref nonnull, nndiscr, nullfields: ref nullfields, _ } => {
             if discr == nndiscr { nonnull.fields.len() } else { nullfields.len() }
         }
@@ -430,7 +566,7 @@ pub fn trans_field_ptr(bcx: @mut Block, r: &Repr, val: ValueRef, discr: Disr,
             assert_eq!(discr, 0);
             struct_field_ptr(bcx, st, val, ix, false)
         }
-        General(ref cases) => {
+        General(_, ref cases) => {
             struct_field_ptr(bcx, &cases[discr], val, ix + 1, true)
         }
         NullablePointer{ nonnull: ref nonnull, nullfields: ref nullfields, nndiscr, _ } => {
@@ -498,24 +634,23 @@ pub fn trans_drop_flag_ptr(bcx: @mut Block, r: &Repr, val: ValueRef) -> ValueRef
 pub fn trans_const(ccx: &mut CrateContext, r: &Repr, discr: Disr,
                    vals: &[ValueRef]) -> ValueRef {
     match *r {
-        CEnum(min, max) => {
+        CEnum(ity, min, max) => {
             assert_eq!(vals.len(), 0);
-            assert!(min <= discr && discr <= max);
+            assert_discr_in_range(ity, min, max, discr);
-            C_disr(ccx, discr)
+            C_integral(ll_inttype(ccx, ity), discr as u64, true)
         }
-        Univariant(ref st, _dro) => {
+        General(ity, ref cases) => {
-            assert_eq!(discr, 0);
-            let contents = build_const_struct(ccx, st, vals);
-            C_struct(contents, st.packed)
-        }
-        General(ref cases) => {
             let case = &cases[discr];
             let max_sz = cases.iter().map(|x| x.size).max().unwrap();
-            let discr_ty = C_disr(ccx, discr);
+            let lldiscr = C_integral(ll_inttype(ccx, ity), discr as u64, true);
-            let contents = build_const_struct(ccx, case,
+            let contents = build_const_struct(ccx, case, ~[lldiscr] + vals);
-                                              ~[discr_ty] + vals);
             C_struct(contents + &[padding(max_sz - case.size)], false)
         }
+        Univariant(ref st, _dro) => {
+            assert!(discr == 0);
+            let contents = build_const_struct(ccx, st, vals);
+            C_struct(contents, st.packed)
+        }
         NullablePointer{ nonnull: ref nonnull, nndiscr, ptrfield, _ } => {
             if discr == nndiscr {
                 C_struct(build_const_struct(ccx, nonnull, vals), false)
@@ -585,9 +720,19 @@ fn roundup(x: u64, a: u64) -> u64 { ((x + (a - 1)) / a) * a }
 pub fn const_get_discrim(ccx: &mut CrateContext, r: &Repr, val: ValueRef)
     -> Disr {
     match *r {
-        CEnum(*) => const_to_uint(val) as Disr,
+        CEnum(ity, _, _) => {
+            match ity {
+                attr::SignedInt(*) => const_to_int(val) as Disr,
+                attr::UnsignedInt(*) => const_to_uint(val) as Disr
+            }
+        }
+        General(ity, _) => {
+            match ity {
+                attr::SignedInt(*) => const_to_int(const_get_elt(ccx, val, [0])) as Disr,
+                attr::UnsignedInt(*) => const_to_uint(const_get_elt(ccx, val, [0])) as Disr
+            }
+        }
         Univariant(*) => 0,
-        General(*) => const_to_uint(const_get_elt(ccx, val, [0])) as Disr,
         NullablePointer{ nndiscr, ptrfield, _ } => {
             if is_null(const_struct_field(ccx, val, ptrfield)) {
                 /* subtraction as uint is ok because nndiscr is either 0 or 1 */
@@ -646,7 +791,3 @@ pub fn is_newtypeish(r: &Repr) -> bool {
         _ => false
     }
 }
-
-fn C_disr(cx: &CrateContext, i: Disr) -> ValueRef {
-    return C_integral(cx.int_type, i, false);
-}

src/librustc/middle/trans/debuginfo.rs

@@ -109,6 +109,7 @@ use std::libc::{c_uint, c_ulonglong, c_longlong};
 use std::ptr;
 use std::unstable::atomics;
 use std::vec;
+use syntax::attr;
 use syntax::codemap::{Span, Pos};
 use syntax::{ast, codemap, ast_util, ast_map, opt_vec};
 use syntax::parse::token;
@@ -1250,7 +1251,7 @@ impl MemberDescriptionFactory for GeneralMemberDescriptionFactory {
                                   -> ~[MemberDescription] {
         // Capture type_rep, so we don't have to copy the struct_defs array
         let struct_defs = match *self.type_rep {
-            adt::General(ref struct_defs) => struct_defs,
+            adt::General(_, ref struct_defs) => struct_defs,
             _ => cx.sess.bug("unreachable")
         };
 
@@ -1399,14 +1400,6 @@ fn prepare_enum_metadata(cx: &mut CrateContext,
         return FinalMetadata(empty_type_metadata);
     }
 
-    // Prepare some data (llvm type, size, align, etc) about the discriminant. This data will be
-    // needed in all of the following cases.
-    let discriminant_llvm_type = Type::enum_discrim(cx);
-    let (discriminant_size, discriminant_align) = size_and_align_of(cx, discriminant_llvm_type);
-
-    assert!(Type::enum_discrim(cx) == cx.int_type);
-    let discriminant_base_type_metadata = type_metadata(cx, ty::mk_int(), codemap::dummy_sp());
-
     let variants = ty::enum_variants(cx.tcx, enum_def_id);
 
     let enumerators_metadata: ~[DIDescriptor] = variants
@@ -1426,26 +1419,34 @@ fn prepare_enum_metadata(cx: &mut CrateContext,
         })
         .collect();
 
-    let discriminant_type_metadata = do enum_name.with_c_str |enum_name| {
+    let discriminant_type_metadata = |inttype| {
-        unsafe {
+        let discriminant_llvm_type = adt::ll_inttype(cx, inttype);
-            llvm::LLVMDIBuilderCreateEnumerationType(
+        let (discriminant_size, discriminant_align) = size_and_align_of(cx, discriminant_llvm_type);
-                DIB(cx),
+        let discriminant_base_type_metadata = type_metadata(cx, match inttype {
-                containing_scope,
+            attr::SignedInt(t) => ty::mk_mach_int(t),
-                enum_name,
+            attr::UnsignedInt(t) => ty::mk_mach_uint(t)
-                file_metadata,
+        }, codemap::dummy_sp());
-                loc.line as c_uint,
+        do enum_name.with_c_str |enum_name| {
-                bytes_to_bits(discriminant_size),
+            unsafe {
-                bytes_to_bits(discriminant_align),
+                llvm::LLVMDIBuilderCreateEnumerationType(
-                create_DIArray(DIB(cx), enumerators_metadata),
+                    DIB(cx),
-                discriminant_base_type_metadata)
+                    containing_scope,
+                    enum_name,
+                    file_metadata,
+                    loc.line as c_uint,
+                    bytes_to_bits(discriminant_size),
+                    bytes_to_bits(discriminant_align),
+                    create_DIArray(DIB(cx), enumerators_metadata),
+                    discriminant_base_type_metadata)
+            }
         }
     };
 
     let type_rep = adt::represent_type(cx, enum_type);
 
     return match *type_rep {
-        adt::CEnum(*) => {
+        adt::CEnum(inttype, _, _) => {
-            FinalMetadata(discriminant_type_metadata)
+            FinalMetadata(discriminant_type_metadata(inttype))
         }
         adt::Univariant(ref struct_def, _) => {
             assert!(variants.len() == 1);
@@ -1466,7 +1467,8 @@ fn prepare_enum_metadata(cx: &mut CrateContext,
                 member_description_factory: member_description_factory
             }
         }
-        adt::General(_) => {
+        adt::General(inttype, _) => {
+            let discriminant_type_metadata = discriminant_type_metadata(inttype);
             let enum_llvm_type = type_of::type_of(cx, enum_type);
             let (enum_type_size, enum_type_align) = size_and_align_of(cx, enum_llvm_type);
 

src/librustc/middle/trans/expr.rs

@@ -1728,7 +1728,7 @@ fn trans_imm_cast(bcx: @mut Block, expr: &ast::Expr,
                 let repr = adt::represent_type(ccx, t_in);
                 let slot = Alloca(bcx, ll_t_in, "");
                 Store(bcx, llexpr, slot);
-                let lldiscrim_a = adt::trans_get_discr(bcx, repr, slot);
+                let lldiscrim_a = adt::trans_get_discr(bcx, repr, slot, Some(Type::i64()));
                 match k_out {
                     cast_integral => int_cast(bcx, ll_t_out,
                                               val_ty(lldiscrim_a),

src/librustc/middle/trans/reflect.rs

@@ -25,7 +25,7 @@ use middle::ty;
 use util::ppaux::ty_to_str;
 
 use std::libc::c_uint;
-use std::option::None;
+use std::option::{Some,None};
 use std::vec;
 use syntax::ast::DefId;
 use syntax::ast;
@@ -308,7 +308,7 @@ impl Reflector {
                 };
                 let mut bcx = fcx.entry_bcx.unwrap();
                 let arg = BitCast(bcx, arg, llptrty);
-                let ret = adt::trans_get_discr(bcx, repr, arg);
+                let ret = adt::trans_get_discr(bcx, repr, arg, Some(ccx.int_type));
                 Store(bcx, ret, fcx.llretptr.unwrap());
                 match fcx.llreturn {
                     Some(llreturn) => cleanup_and_Br(bcx, bcx, llreturn),

src/test/run-pass/small-enum-range-edge.rs

@@ -0,0 +1,32 @@
+// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+/*!
+ * Tests the range assertion wraparound case in trans::middle::adt::load_discr.
+ */
+
+#[repr(u8)]
+enum Eu { Lu = 0, Hu = 255 }
+static CLu: Eu = Lu;
+static CHu: Eu = Hu;
+
+#[repr(i8)]
+enum Es { Ls = -128, Hs = 127 }
+static CLs: Es = Ls;
+static CHs: Es = Hs;
+
+pub fn main() {
+    assert_eq!((Hu as u8) + 1, Lu as u8);
+    assert_eq!((Hs as i8) + 1, Ls as i8);
+    assert_eq!(CLu as u8, Lu as u8);
+    assert_eq!(CHu as u8, Hu as u8);
+    assert_eq!(CLs as i8, Ls as i8);
+    assert_eq!(CHs as i8, Hs as i8);
+}