Miri: dispatch first on the type

src/librustc/ty/sty.rs

@@ -1863,6 +1863,12 @@ impl<'tcx> TyS<'tcx> {
         }
     }
 
+    /// Tests if this is any kind of primitive pointer type (reference, raw pointer, fn pointer).
+    #[inline]
+    pub fn is_any_ptr(&self) -> bool {
+        self.is_region_ptr() || self.is_unsafe_ptr() || self.is_fn_ptr()
+    }
+
     /// Returns `true` if this type is an `Arc<T>`.
     #[inline]
     pub fn is_arc(&self) -> bool {

src/librustc_mir/const_eval.rs

@@ -20,10 +20,10 @@ use rustc_data_structures::fx::FxHashMap;
 use syntax::source_map::{Span, DUMMY_SP};
 
 use crate::interpret::{self,
-    PlaceTy, MPlaceTy, OpTy, ImmTy, Immediate, Scalar,
+    PlaceTy, MPlaceTy, OpTy, ImmTy, Immediate, Scalar, Pointer,
     RawConst, ConstValue,
     InterpResult, InterpErrorInfo, GlobalId, InterpCx, StackPopCleanup,
-    Allocation, AllocId, MemoryKind,
+    Allocation, AllocId, MemoryKind, Memory,
     snapshot, RefTracking, intern_const_alloc_recursive,
 };
 
@@ -397,7 +397,16 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
         )
     }
 
-    fn ptr_op(
+    fn ptr_to_int(
+        _mem: &Memory<'mir, 'tcx, Self>,
+        _ptr: Pointer,
+    ) -> InterpResult<'tcx, u64> {
+        Err(
+            ConstEvalError::NeedsRfc("pointer-to-integer cast".to_string()).into(),
+        )
+    }
+
+    fn binary_ptr_op(
         _ecx: &InterpCx<'mir, 'tcx, Self>,
         _bin_op: mir::BinOp,
         _left: ImmTy<'tcx>,

src/librustc_mir/interpret/cast.rs

@@ -7,22 +7,13 @@ use syntax::symbol::sym;
 use rustc_apfloat::ieee::{Single, Double};
 use rustc_apfloat::{Float, FloatConvert};
 use rustc::mir::interpret::{
-    Scalar, InterpResult, Pointer, PointerArithmetic,
+    Scalar, InterpResult, PointerArithmetic,
 };
 use rustc::mir::CastKind;
 
-use super::{InterpCx, Machine, PlaceTy, OpTy, Immediate, FnVal};
+use super::{InterpCx, Machine, PlaceTy, OpTy, ImmTy, Immediate, FnVal};
 
 impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
-    fn type_is_fat_ptr(&self, ty: Ty<'tcx>) -> bool {
-        match ty.sty {
-            ty::RawPtr(ty::TypeAndMut { ty, .. }) |
-            ty::Ref(_, ty, _) => !self.type_is_sized(ty),
-            ty::Adt(def, _) if def.is_box() => !self.type_is_sized(ty.boxed_ty()),
-            _ => false,
-        }
-    }
-
     pub fn cast(
         &mut self,
         src: OpTy<'tcx, M::PointerTag>,
@@ -37,40 +28,8 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 
             Misc | Pointer(PointerCast::MutToConstPointer) => {
                 let src = self.read_immediate(src)?;
-
-                if self.type_is_fat_ptr(src.layout.ty) {
-                    match (*src, self.type_is_fat_ptr(dest.layout.ty)) {
-                        // pointers to extern types
-                        (Immediate::Scalar(_),_) |
-                        // slices and trait objects to other slices/trait objects
-                        (Immediate::ScalarPair(..), true) => {
-                            // No change to immediate
-                            self.write_immediate(*src, dest)?;
-                        }
-                        // slices and trait objects to thin pointers (dropping the metadata)
-                        (Immediate::ScalarPair(data, _), false) => {
-                            self.write_scalar(data, dest)?;
-                        }
-                    }
-                } else {
-                    match src.layout.variants {
-                        layout::Variants::Single { index } => {
-                            if let Some(discr) =
-                                src.layout.ty.discriminant_for_variant(*self.tcx, index)
-                            {
-                                // Cast from a univariant enum
-                                assert!(src.layout.is_zst());
-                                return self.write_scalar(
-                                    Scalar::from_uint(discr.val, dest.layout.size),
-                                    dest);
-                            }
-                        }
-                        layout::Variants::Multiple { .. } => {},
-                    }
-
-                    let dest_val = self.cast_scalar(src.to_scalar()?, src.layout, dest.layout)?;
-                    self.write_scalar(dest_val, dest)?;
-                }
+                let res = self.cast_immediate(src, dest.layout)?;
+                self.write_immediate(res, dest)?;
             }
 
             Pointer(PointerCast::ReifyFnPointer) => {
@@ -126,36 +85,76 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         Ok(())
     }
 
-    fn cast_scalar(
+    fn cast_immediate(
         &self,
-        val: Scalar<M::PointerTag>,
-        src_layout: TyLayout<'tcx>,
+        src: ImmTy<'tcx, M::PointerTag>,
         dest_layout: TyLayout<'tcx>,
-    ) -> InterpResult<'tcx, Scalar<M::PointerTag>> {
+    ) -> InterpResult<'tcx, Immediate<M::PointerTag>> {
         use rustc::ty::TyKind::*;
-        trace!("Casting {:?}: {:?} to {:?}", val, src_layout.ty, dest_layout.ty);
+        trace!("Casting {:?}: {:?} to {:?}", *src, src.layout.ty, dest_layout.ty);
 
-        match src_layout.ty.sty {
+        match src.layout.ty.sty {
             // Floating point
-            Float(FloatTy::F32) => self.cast_from_float(val.to_f32()?, dest_layout.ty),
-            Float(FloatTy::F64) => self.cast_from_float(val.to_f64()?, dest_layout.ty),
-            // Integer(-like), including fn ptr casts and casts from enums that
-            // are represented as integers (this excludes univariant enums, which
-            // are handled in `cast` directly).
-            _ => {
+            Float(FloatTy::F32) =>
+                return Ok(self.cast_from_float(src.to_scalar()?.to_f32()?, dest_layout.ty)?.into()),
+            Float(FloatTy::F64) =>
+                return Ok(self.cast_from_float(src.to_scalar()?.to_f64()?, dest_layout.ty)?.into()),
+            // The rest is integer/pointer-"like", including fn ptr casts and casts from enums that
+            // are represented as integers.
+            _ =>
                 assert!(
-                    src_layout.ty.is_bool()       || src_layout.ty.is_char()     ||
-                    src_layout.ty.is_enum()       || src_layout.ty.is_integral() ||
-                    src_layout.ty.is_unsafe_ptr() || src_layout.ty.is_fn_ptr()   ||
-                    src_layout.ty.is_region_ptr(),
-                    "Unexpected cast from type {:?}", src_layout.ty
-                );
-                match val.to_bits_or_ptr(src_layout.size, self) {
-                    Err(ptr) => self.cast_from_ptr(ptr, src_layout, dest_layout),
-                    Ok(data) => self.cast_from_int(data, src_layout, dest_layout),
+                    src.layout.ty.is_bool()       || src.layout.ty.is_char()     ||
+                    src.layout.ty.is_enum()       || src.layout.ty.is_integral() ||
+                    src.layout.ty.is_any_ptr(),
+                    "Unexpected cast from type {:?}", src.layout.ty
+                )
+        }
+
+        // Handle cast from a univariant (ZST) enum.
+        match src.layout.variants {
+            layout::Variants::Single { index } => {
+                if let Some(discr) =
+                    src.layout.ty.discriminant_for_variant(*self.tcx, index)
+                {
+                    assert!(src.layout.is_zst());
+                    return Ok(Scalar::from_uint(discr.val, dest_layout.size).into());
                 }
             }
+            layout::Variants::Multiple { .. } => {},
+        }
+
+        // Handle casting the metadata away from a fat pointer.
+        if src.layout.ty.is_unsafe_ptr() && dest_layout.ty.is_unsafe_ptr() &&
+            dest_layout.size != src.layout.size
+        {
+            assert_eq!(src.layout.size, 2*self.memory.pointer_size());
+            assert_eq!(dest_layout.size, self.memory.pointer_size());
+            assert!(dest_layout.ty.is_unsafe_ptr());
+            match *src {
+                Immediate::ScalarPair(data, _) =>
+                    return Ok(data.into()),
+                Immediate::Scalar(..) =>
+                    bug!(
+                        "{:?} input to a fat-to-thin cast ({:?} -> {:?})",
+                        *src, src.layout.ty, dest_layout.ty
+                    ),
+            };
+        }
+
+        // Handle casting any ptr to raw ptr (might be a fat ptr).
+        if src.layout.ty.is_any_ptr() && dest_layout.ty.is_unsafe_ptr()
+        {
+            // The only possible size-unequal case was handled above.
+            assert_eq!(src.layout.size, dest_layout.size);
+            return Ok(*src);
         }
+
+        // For all remaining casts, we either
+        // (a) cast a raw ptr to usize, or
+        // (b) cast from an integer-like (including bool, char, enums).
+        // In both cases we want the bits.
+        let bits = self.force_bits(src.to_scalar()?, src.layout.size)?;
+        Ok(self.cast_from_int(bits, src.layout, dest_layout)?.into())
     }
 
     fn cast_from_int(
@@ -236,31 +235,6 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         }
     }
 
-    fn cast_from_ptr(
-        &self,
-        ptr: Pointer<M::PointerTag>,
-        src_layout: TyLayout<'tcx>,
-        dest_layout: TyLayout<'tcx>,
-    ) -> InterpResult<'tcx, Scalar<M::PointerTag>> {
-        use rustc::ty::TyKind::*;
-
-        match dest_layout.ty.sty {
-            // Casting to a reference or fn pointer is not permitted by rustc,
-            // no need to support it here.
-            RawPtr(_) => Ok(ptr.into()),
-            Int(_) | Uint(_) => {
-                let size = self.memory.pointer_size();
-
-                match self.force_bits(Scalar::Ptr(ptr), size) {
-                    Ok(bits) => self.cast_from_int(bits, src_layout, dest_layout),
-                    Err(_) if dest_layout.size == size => Ok(ptr.into()),
-                    Err(e) => Err(e),
-                }
-            }
-            _ => bug!("invalid MIR: ptr to {:?} cast", dest_layout.ty)
-        }
-    }
-
     fn unsize_into_ptr(
         &mut self,
         src: OpTy<'tcx, M::PointerTag>,

src/librustc_mir/interpret/machine.rs

@@ -165,11 +165,10 @@ pub trait Machine<'mir, 'tcx>: Sized {
         def_id: DefId,
     ) -> InterpResult<'tcx, Cow<'tcx, Allocation>>;
 
-    /// Called for all binary operations on integer(-like) types when one operand is a pointer
-    /// value, and for the `Offset` operation that is inherently about pointers.
+    /// Called for all binary operations where the LHS has pointer type.
     ///
     /// Returns a (value, overflowed) pair if the operation succeeded
-    fn ptr_op(
+    fn binary_ptr_op(
         ecx: &InterpCx<'mir, 'tcx, Self>,
         bin_op: mir::BinOp,
         left: ImmTy<'tcx, Self::PointerTag>,
@@ -234,7 +233,6 @@ pub trait Machine<'mir, 'tcx>: Sized {
         extra: Self::FrameExtra,
     ) -> InterpResult<'tcx>;
 
-    #[inline(always)]
     fn int_to_ptr(
         _mem: &Memory<'mir, 'tcx, Self>,
         int: u64,
@@ -246,11 +244,8 @@ pub trait Machine<'mir, 'tcx>: Sized {
         }).into())
     }
 
-    #[inline(always)]
     fn ptr_to_int(
         _mem: &Memory<'mir, 'tcx, Self>,
         _ptr: Pointer<Self::PointerTag>,
-    ) -> InterpResult<'tcx, u64> {
-        throw_unsup!(ReadPointerAsBytes)
-    }
+    ) -> InterpResult<'tcx, u64>;
 }

src/librustc_mir/interpret/operand.rs

@@ -32,12 +32,21 @@ pub enum Immediate<Tag=(), Id=AllocId> {
     ScalarPair(ScalarMaybeUndef<Tag, Id>, ScalarMaybeUndef<Tag, Id>),
 }
 
-impl<'tcx, Tag> Immediate<Tag> {
-    #[inline]
-    pub fn from_scalar(val: Scalar<Tag>) -> Self {
-        Immediate::Scalar(ScalarMaybeUndef::Scalar(val))
+impl<Tag> From<ScalarMaybeUndef<Tag>> for Immediate<Tag> {
+    #[inline(always)]
+    fn from(val: ScalarMaybeUndef<Tag>) -> Self {
+        Immediate::Scalar(val)
     }
+}
 
+impl<Tag> From<Scalar<Tag>> for Immediate<Tag> {
+    #[inline(always)]
+    fn from(val: Scalar<Tag>) -> Self {
+        Immediate::Scalar(val.into())
+    }
+}
+
+impl<'tcx, Tag> Immediate<Tag> {
     pub fn new_slice(
         val: Scalar<Tag>,
         len: u64,
@@ -182,7 +191,7 @@ impl<'tcx, Tag: Copy> ImmTy<'tcx, Tag>
 {
     #[inline]
     pub fn from_scalar(val: Scalar<Tag>, layout: TyLayout<'tcx>) -> Self {
-        ImmTy { imm: Immediate::from_scalar(val), layout }
+        ImmTy { imm: val.into(), layout }
     }
 
     #[inline]
@@ -240,7 +249,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         let ptr = match self.check_mplace_access(mplace, None)? {
             Some(ptr) => ptr,
             None => return Ok(Some(ImmTy { // zero-sized type
-                imm: Immediate::Scalar(Scalar::zst().into()),
+                imm: Scalar::zst().into(),
                 layout: mplace.layout,
             })),
         };
@@ -251,7 +260,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                     .get(ptr.alloc_id)?
                     .read_scalar(self, ptr, mplace.layout.size)?;
                 Ok(Some(ImmTy {
-                    imm: Immediate::Scalar(scalar),
+                    imm: scalar.into(),
                     layout: mplace.layout,
                 }))
             }
@@ -354,7 +363,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         let field = field.try_into().unwrap();
         let field_layout = op.layout.field(self, field)?;
         if field_layout.is_zst() {
-            let immediate = Immediate::Scalar(Scalar::zst().into());
+            let immediate = Scalar::zst().into();
             return Ok(OpTy { op: Operand::Immediate(immediate), layout: field_layout });
         }
         let offset = op.layout.fields.offset(field);
@@ -364,7 +373,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             // extract fields from types with `ScalarPair` ABI
             Immediate::ScalarPair(a, b) => {
                 let val = if offset.bytes() == 0 { a } else { b };
-                Immediate::Scalar(val)
+                Immediate::from(val)
             },
             Immediate::Scalar(val) =>
                 bug!("field access on non aggregate {:#?}, {:#?}", val, op.layout),
@@ -401,7 +410,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             Deref => self.deref_operand(base)?.into(),
             Subslice { .. } | ConstantIndex { .. } | Index(_) => if base.layout.is_zst() {
                 OpTy {
-                    op: Operand::Immediate(Immediate::Scalar(Scalar::zst().into())),
+                    op: Operand::Immediate(Scalar::zst().into()),
                     // the actual index doesn't matter, so we just pick a convenient one like 0
                     layout: base.layout.field(self, 0)?,
                 }
@@ -425,7 +434,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         let layout = self.layout_of_local(frame, local, layout)?;
         let op = if layout.is_zst() {
             // Do not read from ZST, they might not be initialized
-            Operand::Immediate(Immediate::Scalar(Scalar::zst().into()))
+            Operand::Immediate(Scalar::zst().into())
         } else {
             frame.locals[local].access()?
         };
@@ -556,7 +565,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 Operand::Indirect(MemPlace::from_ptr(ptr, align))
             },
             ConstValue::Scalar(x) =>
-                Operand::Immediate(Immediate::Scalar(tag_scalar(x).into())),
+                Operand::Immediate(tag_scalar(x).into()),
             ConstValue::Slice { data, start, end } => {
                 // We rely on mutability being set correctly in `data` to prevent writes
                 // where none should happen.