implement coercions in MIR

src/librustc_mir/tcx/mod.rs

@@ -16,6 +16,7 @@
 use repr::*;
 use rustc::middle::subst::Substs;
 use rustc::middle::ty::{self, AdtDef, Ty};
+use rustc_front::hir;
 
 #[derive(Copy, Clone, Debug)]
 pub enum LvalueTy<'tcx> {
@@ -123,3 +124,17 @@ impl<'tcx> Mir<'tcx> {
         }
     }
 }
+
+impl BorrowKind {
+    pub fn to_mutbl_lossy(self) -> hir::Mutability {
+        match self {
+            BorrowKind::Mut => hir::MutMutable,
+            BorrowKind::Shared => hir::MutImmutable,
+
+            // We have no type corresponding to a unique imm borrow, so
+            // use `&mut`. It gives all the capabilities of an `&uniq`
+            // and hence is a safe "over approximation".
+            BorrowKind::Unique => hir::MutMutable,
+        }
+    }
+}

src/librustc_trans/trans/base.rs

@@ -55,7 +55,7 @@ use trans::builder::{Builder, noname};
 use trans::callee;
 use trans::cleanup::{self, CleanupMethods, DropHint};
 use trans::closure;
-use trans::common::{Block, C_bool, C_bytes_in_context, C_i32, C_int, C_integral};
+use trans::common::{Block, C_bool, C_bytes_in_context, C_i32, C_int, C_uint, C_integral};
 use trans::common::{C_null, C_struct_in_context, C_u64, C_u8, C_undef};
 use trans::common::{CrateContext, DropFlagHintsMap, Field, FunctionContext};
 use trans::common::{Result, NodeIdAndSpan, VariantInfo};
@@ -577,6 +577,129 @@ pub fn iter_structural_ty<'blk, 'tcx, F>(cx: Block<'blk, 'tcx>,
     return cx;
 }
 
+
+/// Retrieve the information we are losing (making dynamic) in an unsizing
+/// adjustment.
+///
+/// The `old_info` argument is a bit funny. It is intended for use
+/// in an upcast, where the new vtable for an object will be drived
+/// from the old one.
+pub fn unsized_info<'ccx, 'tcx>(ccx: &CrateContext<'ccx, 'tcx>,
+                                source: Ty<'tcx>,
+                                target: Ty<'tcx>,
+                                old_info: Option<ValueRef>,
+                                param_substs: &'tcx Substs<'tcx>)
+                                -> ValueRef {
+    let (source, target) = ccx.tcx().struct_lockstep_tails(source, target);
+    match (&source.sty, &target.sty) {
+        (&ty::TyArray(_, len), &ty::TySlice(_)) => C_uint(ccx, len),
+        (&ty::TyTrait(_), &ty::TyTrait(_)) => {
+            // For now, upcasts are limited to changes in marker
+            // traits, and hence never actually require an actual
+            // change to the vtable.
+            old_info.expect("unsized_info: missing old info for trait upcast")
+        }
+        (_, &ty::TyTrait(box ty::TraitTy { ref principal, .. })) => {
+            // Note that we preserve binding levels here:
+            let substs = principal.0.substs.with_self_ty(source).erase_regions();
+            let substs = ccx.tcx().mk_substs(substs);
+            let trait_ref = ty::Binder(ty::TraitRef { def_id: principal.def_id(),
+                                                      substs: substs });
+            consts::ptrcast(meth::get_vtable(ccx, trait_ref, param_substs),
+                            Type::vtable_ptr(ccx))
+        }
+        _ => ccx.sess().bug(&format!("unsized_info: invalid unsizing {:?} -> {:?}",
+                                     source,
+                                     target))
+    }
+}
+
+/// Coerce `src` to `dst_ty`. `src_ty` must be a thin pointer.
+pub fn unsize_thin_ptr<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
+                                   src: ValueRef,
+                                   src_ty: Ty<'tcx>,
+                                   dst_ty: Ty<'tcx>)
+                                   -> (ValueRef, ValueRef) {
+    debug!("unsize_thin_ptr: {:?} => {:?}", src_ty, dst_ty);
+    match (&src_ty.sty, &dst_ty.sty) {
+        (&ty::TyBox(a), &ty::TyBox(b)) |
+        (&ty::TyRef(_, ty::TypeAndMut { ty: a, .. }),
+         &ty::TyRef(_, ty::TypeAndMut { ty: b, .. })) |
+        (&ty::TyRef(_, ty::TypeAndMut { ty: a, .. }),
+         &ty::TyRawPtr(ty::TypeAndMut { ty: b, .. })) |
+        (&ty::TyRawPtr(ty::TypeAndMut { ty: a, .. }),
+         &ty::TyRawPtr(ty::TypeAndMut { ty: b, .. })) => {
+            assert!(common::type_is_sized(bcx.tcx(), a));
+            let ptr_ty = type_of::in_memory_type_of(bcx.ccx(), b).ptr_to();
+            (PointerCast(bcx, src, ptr_ty),
+             unsized_info(bcx.ccx(), a, b, None, bcx.fcx.param_substs))
+        }
+        _ => bcx.sess().bug(
+            &format!("unsize_thin_ptr: called on bad types"))
+    }
+}
+
+/// Coerce `src`, which is a reference to a value of type `src_ty`,
+/// to a value of type `dst_ty` and store the result in `dst`
+pub fn coerce_unsized_into<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
+                                       src: ValueRef,
+                                       src_ty: Ty<'tcx>,
+                                       dst: ValueRef,
+                                       dst_ty: Ty<'tcx>) {
+    match (&src_ty.sty, &dst_ty.sty) {
+        (&ty::TyBox(..), &ty::TyBox(..)) |
+        (&ty::TyRef(..), &ty::TyRef(..)) |
+        (&ty::TyRef(..), &ty::TyRawPtr(..)) |
+        (&ty::TyRawPtr(..), &ty::TyRawPtr(..)) => {
+            let (base, info) = if common::type_is_fat_ptr(bcx.tcx(), src_ty) {
+                // fat-ptr to fat-ptr unsize preserves the vtable
+                load_fat_ptr(bcx, src, src_ty)
+            } else {
+                let base = load_ty(bcx, src, src_ty);
+                unsize_thin_ptr(bcx, base, src_ty, dst_ty)
+            };
+            store_fat_ptr(bcx, base, info, dst, dst_ty);
+        }
+
+        // This can be extended to enums and tuples in the future.
+        // (&ty::TyEnum(def_id_a, _), &ty::TyEnum(def_id_b, _)) |
+        (&ty::TyStruct(def_a, _), &ty::TyStruct(def_b, _)) => {
+            assert_eq!(def_a, def_b);
+
+            let src_repr = adt::represent_type(bcx.ccx(), src_ty);
+            let src_fields = match &*src_repr {
+                &adt::Repr::Univariant(ref s, _) => &s.fields,
+                _ => bcx.sess().bug("struct has non-univariant repr")
+            };
+            let dst_repr = adt::represent_type(bcx.ccx(), dst_ty);
+            let dst_fields = match &*dst_repr {
+                &adt::Repr::Univariant(ref s, _) => &s.fields,
+                _ => bcx.sess().bug("struct has non-univariant repr")
+            };
+
+            let iter = src_fields.iter().zip(dst_fields).enumerate();
+            for (i, (src_fty, dst_fty)) in iter {
+                if type_is_zero_size(bcx.ccx(), dst_fty) { continue; }
+
+                let src_f = adt::trans_field_ptr(bcx, &src_repr, src, 0, i);
+                let dst_f = adt::trans_field_ptr(bcx, &dst_repr, dst, 0, i);
+                if src_fty == dst_fty {
+                    memcpy_ty(bcx, dst_f, src_f, src_fty);
+                } else {
+                    coerce_unsized_into(
+                        bcx,
+                        src_f, src_fty,
+                        dst_f, dst_fty
+                    );
+                }
+            }
+        }
+        _ => bcx.sess().bug(&format!("coerce_unsized_into: invalid coercion {:?} -> {:?}",
+                                     src_ty,
+                                     dst_ty))
+    }
+}
+
 pub fn cast_shift_expr_rhs(cx: Block,
                            op: hir::BinOp_,
                            lhs: ValueRef,

src/librustc_trans/trans/common.rs

@@ -1223,4 +1223,4 @@ pub fn get_static_val<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
     } else {
         base::get_extern_const(ccx, did, ty)
     }
-}
+}

src/librustc_trans/trans/consts.rs

@@ -410,7 +410,7 @@ pub fn const_expr<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>,
                     .expect("consts: unsizing got non-pointer target type").ty;
                 let ptr_ty = type_of::in_memory_type_of(cx, unsized_ty).ptr_to();
                 let base = ptrcast(base, ptr_ty);
-                let info = expr::unsized_info(cx, pointee_ty, unsized_ty,
+                let info = base::unsized_info(cx, pointee_ty, unsized_ty,
                                               old_info, param_substs);
 
                 if old_info.is_none() {

src/librustc_trans/trans/expr.rs

@@ -326,42 +326,6 @@ pub fn copy_fat_ptr(bcx: Block, src_ptr: ValueRef, dst_ptr: ValueRef) {
     Store(bcx, Load(bcx, get_meta(bcx, src_ptr)), get_meta(bcx, dst_ptr));
 }
 
-/// Retrieve the information we are losing (making dynamic) in an unsizing
-/// adjustment.
-///
-/// The `old_info` argument is a bit funny. It is intended for use
-/// in an upcast, where the new vtable for an object will be drived
-/// from the old one.
-pub fn unsized_info<'ccx, 'tcx>(ccx: &CrateContext<'ccx, 'tcx>,
-                                source: Ty<'tcx>,
-                                target: Ty<'tcx>,
-                                old_info: Option<ValueRef>,
-                                param_substs: &'tcx Substs<'tcx>)
-                                -> ValueRef {
-    let (source, target) = ccx.tcx().struct_lockstep_tails(source, target);
-    match (&source.sty, &target.sty) {
-        (&ty::TyArray(_, len), &ty::TySlice(_)) => C_uint(ccx, len),
-        (&ty::TyTrait(_), &ty::TyTrait(_)) => {
-            // For now, upcasts are limited to changes in marker
-            // traits, and hence never actually require an actual
-            // change to the vtable.
-            old_info.expect("unsized_info: missing old info for trait upcast")
-        }
-        (_, &ty::TyTrait(box ty::TraitTy { ref principal, .. })) => {
-            // Note that we preserve binding levels here:
-            let substs = principal.0.substs.with_self_ty(source).erase_regions();
-            let substs = ccx.tcx().mk_substs(substs);
-            let trait_ref = ty::Binder(ty::TraitRef { def_id: principal.def_id(),
-                                                      substs: substs });
-            consts::ptrcast(meth::get_vtable(ccx, trait_ref, param_substs),
-                            Type::vtable_ptr(ccx))
-        }
-        _ => ccx.sess().bug(&format!("unsized_info: invalid unsizing {:?} -> {:?}",
-                                     source,
-                                     target))
-    }
-}
-
 fn adjustment_required<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
                                    expr: &hir::Expr) -> bool {
     let adjustment = match bcx.tcx().tables.borrow().adjustments.get(&expr.id).cloned() {

src/librustc_trans/trans/mir/lvalue.rs

@@ -85,7 +85,9 @@ impl<'bcx, 'tcx> MirContext<'bcx, 'tcx> {
             mir::Lvalue::Arg(index) => self.args[index as usize],
             mir::Lvalue::Static(def_id) => {
                 let const_ty = self.mir.lvalue_ty(tcx, lvalue);
-                LvalueRef::new(common::get_static_val(ccx, def_id, const_ty.to_ty(tcx)), const_ty)
+                LvalueRef::new_sized(
+                    common::get_static_val(ccx, def_id, const_ty.to_ty(tcx)),
+                    const_ty)
             },
             mir::Lvalue::ReturnPointer => {
                 let return_ty = bcx.monomorphize(&self.mir.return_ty);

src/librustc_trans/trans/mir/rvalue.rs

@@ -46,20 +46,35 @@ impl<'bcx, 'tcx> MirContext<'bcx, 'tcx> {
             }
 
             mir::Rvalue::Cast(mir::CastKind::Unsize, ref operand, cast_ty) => {
-                let expr_ty =
-                    bcx.monomorphize(&self.mir.operand_ty(bcx.tcx(), operand));
-                let cast_ty =
-                    bcx.monomorphize(&cast_ty);
-                if expr_ty == cast_ty {
-                    debug!("trans_rvalue: trivial unsize at {:?}", expr_ty);
-                    self.trans_operand_into(bcx, lldest, operand);
+                if common::type_is_fat_ptr(bcx.tcx(), cast_ty) {
+                    let (bcx, temp) = self.trans_rvalue_operand(bcx, rvalue);
+                    self.store_operand(bcx, lldest, temp);
                     return bcx;
                 }
-                unimplemented!()
-            }
 
-            mir::Rvalue::Cast(..) => {
-                unimplemented!()
+                // Unsize of a nontrivial struct. I would prefer for
+                // this to be eliminated by MIR translation, but
+                // `CoerceUnsized` can be passed by a where-clause,
+                // so the (generic) MIR may not be able to expand it.
+                let operand = self.trans_operand(bcx, operand);
+                match operand.val {
+                    OperandValue::FatPtr(..) => unreachable!(),
+                    OperandValue::Imm(llval) => {
+                        // ugly alloca.
+                        debug!("trans_rvalue: creating ugly alloca");
+                        let lltemp = base::alloc_ty(bcx, operand.ty, "__unsize_temp");
+                        base::store_ty(bcx, llval, lltemp, operand.ty);
+                        base::coerce_unsized_into(bcx,
+                                                  lltemp, operand.ty,
+                                                  lldest, cast_ty);
+                    }
+                    OperandValue::Ref(llref) => {
+                        base::coerce_unsized_into(bcx,
+                                                  llref, operand.ty,
+                                                  lldest, cast_ty);
+                    }
+                }
+                bcx
             }
 
             mir::Rvalue::Repeat(ref elem, ref count) => {
@@ -125,30 +140,74 @@ impl<'bcx, 'tcx> MirContext<'bcx, 'tcx> {
                 (bcx, operand)
             }
 
-            mir::Rvalue::Cast(mir::CastKind::Unsize, _, _) => {
-                unimplemented!()
+            mir::Rvalue::Cast(ref kind, ref operand, cast_ty) => {
+                let operand = self.trans_operand(bcx, operand);
+                debug!("cast operand is {}", operand.repr(bcx));
+                let cast_ty = bcx.monomorphize(&cast_ty);
+
+                let val = match *kind {
+                    mir::CastKind::ReifyFnPointer |
+                    mir::CastKind::UnsafeFnPointer => {
+                        // these are no-ops at the LLVM level
+                        operand.val
+                    }
+                    mir::CastKind::Unsize => {
+                        // unsize targets other than to a fat pointer currently
+                        // can't be operands.
+                        assert!(common::type_is_fat_ptr(bcx.tcx(), cast_ty));
+
+                        match operand.val {
+                            OperandValue::FatPtr(..) => {
+                                // unsize from a fat pointer - this is a
+                                // "trait-object-to-supertrait" coercion, for
+                                // example,
+                                //   &'a fmt::Debug+Send => &'a fmt::Debug,
+                                // and is a no-op at the LLVM level
+                                operand.val
+                            }
+                            OperandValue::Imm(lldata) => {
+                                // "standard" unsize
+                                let (lldata, llextra) =
+                                    base::unsize_thin_ptr(bcx, lldata,
+                                                          operand.ty, cast_ty);
+                                OperandValue::FatPtr(lldata, llextra)
+                            }
+                            OperandValue::Ref(_) => {
+                                bcx.sess().bug(
+                                    &format!("by-ref operand {} in trans_rvalue_operand",
+                                             operand.repr(bcx)));
+                            }
+                        }
+                    }
+                    mir::CastKind::Misc => unimplemented!()
+                };
+                (bcx, OperandRef {
+                    val: val,
+                    ty: cast_ty
+                })
             }
 
-            mir::Rvalue::Cast(..) => {
-                unimplemented!()
-            }
-
-            mir::Rvalue::Ref(_, _, ref lvalue) => {
+            mir::Rvalue::Ref(_, bk, ref lvalue) => {
                 let tr_lvalue = self.trans_lvalue(bcx, lvalue);
 
                 let ty = tr_lvalue.ty.to_ty(bcx.tcx());
+                let ref_ty = bcx.tcx().mk_ref(
+                    bcx.tcx().mk_region(ty::ReStatic),
+                    ty::TypeAndMut { ty: ty, mutbl: bk.to_mutbl_lossy() }
+                );
+
                 // Note: lvalues are indirect, so storing the `llval` into the
                 // destination effectively creates a reference.
                 if common::type_is_sized(bcx.tcx(), ty) {
                     (bcx, OperandRef {
                         val: OperandValue::Imm(tr_lvalue.llval),
-                        ty: ty,
+                        ty: ref_ty,
                     })
                 } else {
                     (bcx, OperandRef {
                         val: OperandValue::FatPtr(tr_lvalue.llval,
                                                   tr_lvalue.llextra),
-                        ty: ty,
+                        ty: ref_ty,
                     })
                 }
             }

src/test/run-pass/mir_coercions.rs

@@ -0,0 +1,76 @@
+// Copyright 2015 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.
+
+#![feature(rustc_attrs, coerce_unsized, unsize)]
+
+use std::ops::CoerceUnsized;
+use std::marker::Unsize;
+
+#[rustc_mir]
+fn identity_coercion(x: &(Fn(u32)->u32 + Send)) -> &Fn(u32)->u32 {
+    x
+}
+#[rustc_mir]
+fn fn_coercions(f: &fn(u32) -> u32) ->
+    (unsafe fn(u32) -> u32,
+     &(Fn(u32) -> u32+Send))
+{
+    (*f, f)
+}
+
+#[rustc_mir]
+fn simple_array_coercion(x: &[u8; 3]) -> &[u8] { x }
+
+fn square(a: u32) -> u32 { a * a }
+
+#[derive(PartialEq,Eq)]
+struct PtrWrapper<'a, T: 'a+?Sized>(u32, u32, (), &'a T);
+impl<'a, T: ?Sized+Unsize<U>, U: ?Sized>
+    CoerceUnsized<PtrWrapper<'a, U>> for PtrWrapper<'a, T> {}
+
+struct TrivPtrWrapper<'a, T: 'a+?Sized>(&'a T);
+impl<'a, T: ?Sized+Unsize<U>, U: ?Sized>
+    CoerceUnsized<TrivPtrWrapper<'a, U>> for TrivPtrWrapper<'a, T> {}
+
+#[rustc_mir]
+fn coerce_ptr_wrapper(p: PtrWrapper<[u8; 3]>) -> PtrWrapper<[u8]> {
+    p
+}
+
+#[rustc_mir]
+fn coerce_triv_ptr_wrapper(p: TrivPtrWrapper<[u8; 3]>) -> TrivPtrWrapper<[u8]> {
+    p
+}
+
+#[rustc_mir]
+fn coerce_fat_ptr_wrapper(p: PtrWrapper<Fn(u32) -> u32+Send>)
+                          -> PtrWrapper<Fn(u32) -> u32> {
+    p
+}
+
+
+fn main() {
+    let a = [0,1,2];
+    let square_local : fn(u32) -> u32 = square;
+    let (f,g) = fn_coercions(&square_local);
+    assert_eq!(f as usize, square as usize);
+    assert_eq!(g(4), 16);
+    assert_eq!(identity_coercion(g)(5), 25);
+
+    assert_eq!(simple_array_coercion(&a), &a);
+    let w = coerce_ptr_wrapper(PtrWrapper(2,3,(),&a));
+    assert!(w == PtrWrapper(2,3,(),&a) as PtrWrapper<[u8]>);
+
+    let w = coerce_triv_ptr_wrapper(TrivPtrWrapper(&a));
+    assert_eq!(&w.0, &a);
+
+    let z = coerce_fat_ptr_wrapper(PtrWrapper(2,3,(),&square_local));
+    assert_eq!((z.3)(6), 36);
+}