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Miri: use more specialized Scalar::from_ constructors where appropriate #70508

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Mar 29, 2020
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Miri: use more specialized Scalar::from_ constructors where appropriate #70508

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1a0e69d
use more specialized Scalar::from_ constructors where appropriate
RalfJung Mar 28, 2020
1f53fdc
get rid of useless back-and-forth cast
RalfJung Mar 28, 2020
bd9e046
refmt
RalfJung Mar 28, 2020
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2 changes: 1 addition & 1 deletion src/librustc_mir/interpret/cast.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -208,7 +208,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {

Char => {
// `u8` to `char` cast
Ok(Scalar::from_uint(u8::try_from(v).unwrap(), Size::from_bytes(4)))
Ok(Scalar::from_u32(u8::try_from(v).unwrap().into()))
}

// Casts to bool are not permitted by rustc, no need to handle them here.
Expand Down
8 changes: 5 additions & 3 deletions src/librustc_mir/interpret/intrinsics.rs
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Expand Up @@ -2,6 +2,8 @@
//! looking at their MIR. Intrinsics/functions supported here are shared by CTFE
//! and miri.

use std::convert::TryFrom;

use rustc::mir::{
self,
interpret::{ConstValue, GlobalId, InterpResult, Scalar},
Expand Down Expand Up @@ -220,7 +222,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
sym::discriminant_value => {
let place = self.deref_operand(args[0])?;
let discr_val = self.read_discriminant(place.into())?.0;
self.write_scalar(Scalar::from_uint(discr_val, dest.layout.size), dest)?;
self.write_scalar(Scalar::from_u64(u64::try_from(discr_val).unwrap()), dest)?;
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@eddyb this is where Miri would now ICE for too big discriminants. (And I am not entirely sure what happens for negative discriminants, TBH...)

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Looking at this, I think for signed 64bit discriminants we appropriately truncate and everything is okay. (I tried to find a way to share that code there with cast.rs but found no good way.)

For negative discriminants with repr(i128) this will ICE, but well, these just cannot be represented properly in a u64...

}
sym::unchecked_shl
| sym::unchecked_shr
Expand Down Expand Up @@ -275,7 +277,6 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
}

sym::ptr_offset_from => {
let isize_layout = self.layout_of(self.tcx.types.isize)?;
let a = self.read_immediate(args[0])?.to_scalar()?;
let b = self.read_immediate(args[1])?.to_scalar()?;

Expand All @@ -292,7 +293,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
let a = a.to_machine_usize(self)?;
let b = b.to_machine_usize(self)?;
if a == b && a != 0 {
self.write_scalar(Scalar::from_int(0, isize_layout.size), dest)?;
self.write_scalar(Scalar::from_machine_isize(0, self), dest)?;
true
} else {
false
Expand All @@ -312,6 +313,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
);
}
let usize_layout = self.layout_of(self.tcx.types.usize)?;
let isize_layout = self.layout_of(self.tcx.types.isize)?;
let a_offset = ImmTy::from_uint(a.offset.bytes(), usize_layout);
let b_offset = ImmTy::from_uint(b.offset.bytes(), usize_layout);
let (val, _overflowed, _ty) =
Expand Down
10 changes: 3 additions & 7 deletions src/librustc_mir/interpret/operand.rs
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Expand Up @@ -54,10 +54,7 @@ impl<Tag> From<Pointer<Tag>> for Immediate<Tag> {

impl<'tcx, Tag> Immediate<Tag> {
pub fn new_slice(val: Scalar<Tag>, len: u64, cx: &impl HasDataLayout) -> Self {
Immediate::ScalarPair(
val.into(),
Scalar::from_uint(len, cx.data_layout().pointer_size).into(),
)
Immediate::ScalarPair(val.into(), Scalar::from_machine_usize(len, cx).into())
}

pub fn new_dyn_trait(val: Scalar<Tag>, vtable: Pointer<Tag>) -> Self {
Expand Down Expand Up @@ -621,7 +618,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
let real_discr = if discr_val.layout.abi.is_signed() {
// going from layout tag type to typeck discriminant type
// requires first sign extending with the discriminant layout
let sexted = sign_extend(bits_discr, discr_val.layout.size) as i128;
let sexted = sign_extend(bits_discr, discr_val.layout.size);
// and then zeroing with the typeck discriminant type
let discr_ty = rval
.layout
Expand All @@ -631,8 +628,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
.repr
.discr_type();
let size = layout::Integer::from_attr(self, discr_ty).size();
let truncatee = sexted as u128;
truncate(truncatee, size)
truncate(sexted, size)
} else {
bits_discr
};
Expand Down
6 changes: 3 additions & 3 deletions src/librustc_mir/interpret/place.rs
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Expand Up @@ -180,7 +180,7 @@ impl<'tcx, Tag> MPlaceTy<'tcx, Tag> {
#[inline]
pub fn dangling(layout: TyLayout<'tcx>, cx: &impl HasDataLayout) -> Self {
let align = layout.align.abi;
let ptr = Scalar::from_uint(align.bytes(), cx.pointer_size());
let ptr = Scalar::from_machine_usize(align.bytes(), cx);
// `Poison` this to make sure that the pointer value `ptr` is never observable by the program.
MPlaceTy { mplace: MemPlace { ptr, align, meta: MemPlaceMeta::Poison }, layout }
}
Expand Down Expand Up @@ -504,7 +504,7 @@ where
// implement this.
ty::Array(inner, _) => (MemPlaceMeta::None, self.tcx.mk_array(inner, inner_len)),
ty::Slice(..) => {
let len = Scalar::from_uint(inner_len, self.pointer_size());
let len = Scalar::from_machine_usize(inner_len, self);
(MemPlaceMeta::Meta(len), base.layout.ty)
}
_ => bug!("cannot subslice non-array type: `{:?}`", base.layout.ty),
Expand Down Expand Up @@ -1044,7 +1044,7 @@ where
kind: MemoryKind<M::MemoryKind>,
) -> MPlaceTy<'tcx, M::PointerTag> {
let ptr = self.memory.allocate_bytes(str.as_bytes(), kind);
let meta = Scalar::from_uint(u128::try_from(str.len()).unwrap(), self.pointer_size());
let meta = Scalar::from_machine_usize(u64::try_from(str.len()).unwrap(), self);
let mplace = MemPlace {
ptr: ptr.into(),
align: Align::from_bytes(1).unwrap(),
Expand Down
8 changes: 3 additions & 5 deletions src/librustc_mir/interpret/step.rs
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Expand Up @@ -3,7 +3,7 @@
//! The main entry point is the `step` method.

use rustc::mir;
use rustc::mir::interpret::{InterpResult, PointerArithmetic, Scalar};
use rustc::mir::interpret::{InterpResult, Scalar};
use rustc::ty::layout::LayoutOf;

use super::{InterpCx, Machine};
Expand Down Expand Up @@ -229,8 +229,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
let src = self.eval_place(place)?;
let mplace = self.force_allocation(src)?;
let len = mplace.len(self)?;
let size = self.pointer_size();
self.write_scalar(Scalar::from_uint(len, size), dest)?;
self.write_scalar(Scalar::from_machine_usize(len, self), dest)?;
}

AddressOf(_, ref place) | Ref(_, _, ref place) => {
Expand All @@ -254,8 +253,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
!layout.is_unsized(),
"SizeOf nullary MIR operator called for unsized type"
);
let size = self.pointer_size();
self.write_scalar(Scalar::from_uint(layout.size.bytes(), size), dest)?;
self.write_scalar(Scalar::from_machine_usize(layout.size.bytes(), self), dest)?;
}

Cast(kind, ref operand, _) => {
Expand Down