Rollup merge of rust-lang#62946 - RalfJung:miri_type_dispatch_first, r=oli-obk

Miri: dispatch first on the type

Based on the fact that Miri now always has intptrcast available, we can change binops and casts to first check the type of the source operand and then decide based on that what to do, instead of considering the value (pointer vs bits) first.

Author: Centril

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, InterpError, 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, InterpError,
+    Scalar, InterpResult, PointerArithmetic, InterpError,
 };
 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> {
-        err!(ReadPointerAsBytes)
-    }
+    ) -> InterpResult<'tcx, u64>;
 }

src/librustc_mir/interpret/operand.rs

@@ -33,12 +33,21 @@ 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,
@@ -183,7 +192,7 @@ 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]
@@ -241,7 +250,7 @@ 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,
             })),
         };
@@ -252,7 +261,7 @@ 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()?
         };
@@ -553,7 +562,7 @@ 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.