rust/src/terminator/intrinsic.rs

use rustc::hir::def_id::DefId;
use rustc::mir;
use rustc::ty::layout::Layout;
use rustc::ty::subst::Substs;
use rustc::ty::{self, Ty};

use error::{EvalError, EvalResult};
use eval_context::EvalContext;
use lvalue::{Lvalue, LvalueExtra};
use operator;
use value::{PrimVal, PrimValKind, Value};

impl<'a, 'tcx> EvalContext<'a, 'tcx> {
    pub(super) fn call_intrinsic(
        &mut self,
        def_id: DefId,
        substs: &'tcx Substs<'tcx>,
        args: &[mir::Operand<'tcx>],
        dest: Lvalue<'tcx>,
        dest_ty: Ty<'tcx>,
        dest_layout: &'tcx Layout,
        target: mir::BasicBlock,
    ) -> EvalResult<'tcx, ()> {
        let arg_vals: EvalResult<Vec<Value>> = args.iter()
            .map(|arg| self.eval_operand(arg))
            .collect();
        let arg_vals = arg_vals?;
        let i32 = self.tcx.types.i32;
        let isize = self.tcx.types.isize;
        let usize = self.tcx.types.usize;
        let f32 = self.tcx.types.f32;
        let f64 = self.tcx.types.f64;

        let intrinsic_name = &self.tcx.item_name(def_id).as_str()[..];
        match intrinsic_name {
            "add_with_overflow" =>
                self.intrinsic_with_overflow(mir::BinOp::Add, &args[0], &args[1], dest, dest_ty)?,

            "sub_with_overflow" =>
                self.intrinsic_with_overflow(mir::BinOp::Sub, &args[0], &args[1], dest, dest_ty)?,

            "mul_with_overflow" =>
                self.intrinsic_with_overflow(mir::BinOp::Mul, &args[0], &args[1], dest, dest_ty)?,


            "arith_offset" => {
                let ptr = arg_vals[0].read_ptr(&self.memory)?;
                let offset = self.value_to_primval(arg_vals[1], isize)?.to_i64()?;
                let new_ptr = ptr.signed_offset(offset);
                self.write_primval(dest, PrimVal::Ptr(new_ptr), dest_ty)?;
            }

            "assume" => {
                let bool = self.tcx.types.bool;
                let cond = self.value_to_primval(arg_vals[0], bool)?.to_bool()?;
                if !cond { return Err(EvalError::AssumptionNotHeld); }
            }

            "atomic_load" |
            "atomic_load_relaxed" |
            "atomic_load_acq" |
            "volatile_load" => {
                let ty = substs.type_at(0);
                let ptr = arg_vals[0].read_ptr(&self.memory)?;
                self.write_value(Value::ByRef(ptr), dest, ty)?;
            }

            "atomic_store" |
            "volatile_store" => {
                let ty = substs.type_at(0);
                let dest = arg_vals[0].read_ptr(&self.memory)?;
                self.write_value_to_ptr(arg_vals[1], dest, ty)?;
            }

            "atomic_fence_acq" => {
                // we are inherently singlethreaded and singlecored, this is a nop
            }

            "atomic_xchg" => {
                let ty = substs.type_at(0);
                let ptr = arg_vals[0].read_ptr(&self.memory)?;
                let change = self.value_to_primval(arg_vals[1], ty)?;
                let old = self.read_value(ptr, ty)?;
                let old = match old {
                    Value::ByVal(val) => val,
                    Value::ByRef(_) => bug!("just read the value, can't be byref"),
                    Value::ByValPair(..) => bug!("atomic_xchg doesn't work with nonprimitives"),
                };
                self.write_primval(dest, old, ty)?;
                self.write_primval(Lvalue::from_ptr(ptr), change, ty)?;
            }

            "atomic_cxchg" => {
                let ty = substs.type_at(0);
                let ptr = arg_vals[0].read_ptr(&self.memory)?;
                let expect_old = self.value_to_primval(arg_vals[1], ty)?;
                let change = self.value_to_primval(arg_vals[2], ty)?;
                let old = self.read_value(ptr, ty)?;
                let old = match old {
                    Value::ByVal(val) => val,
                    Value::ByRef(_) => bug!("just read the value, can't be byref"),
                    Value::ByValPair(..) => bug!("atomic_cxchg doesn't work with nonprimitives"),
                };
                let kind = self.ty_to_primval_kind(ty)?;
                let (val, _) = operator::binary_op(mir::BinOp::Eq, old, kind, expect_old, kind)?;
                let dest = self.force_allocation(dest)?.to_ptr();
                self.write_pair_to_ptr(old, val, dest, dest_ty)?;
                self.write_primval(Lvalue::from_ptr(ptr), change, ty)?;
            }

            "atomic_xadd_relaxed" => {
                let ty = substs.type_at(0);
                let ptr = arg_vals[0].read_ptr(&self.memory)?;
                let change = self.value_to_primval(arg_vals[1], ty)?;
                let old = self.read_value(ptr, ty)?;
                let old = match old {
                    Value::ByVal(val) => val,
                    Value::ByRef(_) => bug!("just read the value, can't be byref"),
                    Value::ByValPair(..) => bug!("atomic_xadd_relaxed doesn't work with nonprimitives"),
                };
                self.write_primval(dest, old, ty)?;
                let kind = self.ty_to_primval_kind(ty)?;
                // FIXME: what do atomics do on overflow?
                let (val, _) = operator::binary_op(mir::BinOp::Add, old, kind, change, kind)?;
                self.write_primval(Lvalue::from_ptr(ptr), val, ty)?;
            },

            "atomic_xsub_rel" => {
                let ty = substs.type_at(0);
                let ptr = arg_vals[0].read_ptr(&self.memory)?;
                let change = self.value_to_primval(arg_vals[1], ty)?;
                let old = self.read_value(ptr, ty)?;
                let old = match old {
                    Value::ByVal(val) => val,
                    Value::ByRef(_) => bug!("just read the value, can't be byref"),
                    Value::ByValPair(..) => bug!("atomic_xsub_rel doesn't work with nonprimitives"),
                };
                self.write_primval(dest, old, ty)?;
                let kind = self.ty_to_primval_kind(ty)?;
                // FIXME: what do atomics do on overflow?
                let (val, _) = operator::binary_op(mir::BinOp::Sub, old, kind, change, kind)?;
                self.write_primval(Lvalue::from_ptr(ptr), val, ty)?;
            }

            "breakpoint" => unimplemented!(), // halt miri

            "copy" |
            "copy_nonoverlapping" => {
                // FIXME: check whether overlapping occurs
                let elem_ty = substs.type_at(0);
                let elem_size = self.type_size(elem_ty)?.expect("cannot copy unsized value");
                let elem_align = self.type_align(elem_ty)?;
                let src = arg_vals[0].read_ptr(&self.memory)?;
                let dest = arg_vals[1].read_ptr(&self.memory)?;
                let count = self.value_to_primval(arg_vals[2], usize)?.to_u64()?;
                self.memory.copy(src, dest, count * elem_size, elem_align)?;
            }

            "ctpop" |
            "cttz" |
            "ctlz" |
            "bswap" => {
                let ty = substs.type_at(0);
                let num = self.value_to_primval(arg_vals[0], ty)?;
                let kind = self.ty_to_primval_kind(ty)?;
                let num = numeric_intrinsic(intrinsic_name, num, kind)?;
                self.write_primval(dest, num, ty)?;
            }

            "discriminant_value" => {
                let ty = substs.type_at(0);
                let adt_ptr = arg_vals[0].read_ptr(&self.memory)?;
                let discr_val = self.read_discriminant_value(adt_ptr, ty)?;
                self.write_primval(dest, PrimVal::Bytes(discr_val), dest_ty)?;
            }

            "drop_in_place" => {
                let ty = substs.type_at(0);
                trace!("drop in place on {}", ty);
                let ptr_ty = self.tcx.mk_mut_ptr(ty);
                let lvalue = match self.follow_by_ref_value(arg_vals[0], ptr_ty)? {
                    Value::ByRef(_) => bug!("follow_by_ref_value returned ByRef"),
                    Value::ByVal(value) => Lvalue::from_ptr(value.to_ptr()?),
                    Value::ByValPair(ptr, extra) => Lvalue::Ptr {
                        ptr: ptr.to_ptr()?,
                        extra: match self.tcx.struct_tail(ty).sty {
                            ty::TyDynamic(..) => LvalueExtra::Vtable(extra.to_ptr()?),
                            ty::TyStr | ty::TySlice(_) => LvalueExtra::Length(extra.to_u64()?),
                            _ => bug!("invalid fat pointer type: {}", ptr_ty),
                        },
                    },
                };
                let mut drops = Vec::new();
                self.drop(lvalue, ty, &mut drops)?;
                let span = {
                    let frame = self.frame();
                    frame.mir[frame.block].terminator().source_info.span
                };
                // need to change the block before pushing the drop impl stack frames
                // we could do this for all intrinsics before evaluating the intrinsics, but if
                // the evaluation fails, we should not have moved forward
                self.goto_block(target);
                return self.eval_drop_impls(drops, span);
            }

            "fabsf32" => {
                let f = self.value_to_primval(arg_vals[2], f32)?.to_f32()?;
                self.write_primval(dest, PrimVal::from_f32(f.abs()), dest_ty)?;
            }

            "fabsf64" => {
                let f = self.value_to_primval(arg_vals[2], f64)?.to_f64()?;
                self.write_primval(dest, PrimVal::from_f64(f.abs()), dest_ty)?;
            }

            "fadd_fast" => {
                let ty = substs.type_at(0);
                let kind = self.ty_to_primval_kind(ty)?;
                let a = self.value_to_primval(arg_vals[0], ty)?;
                let b = self.value_to_primval(arg_vals[0], ty)?;
                let result = operator::binary_op(mir::BinOp::Add, a, kind, b, kind)?;
                self.write_primval(dest, result.0, dest_ty)?;
            }

            "likely" |
            "unlikely" |
            "forget" => {}

            "init" => {
                let size = self.type_size(dest_ty)?.expect("cannot zero unsized value");;
                let init = |this: &mut Self, val: Option<Value>| {
                    let zero_val = match val {
                        Some(Value::ByRef(ptr)) => {
                            this.memory.write_repeat(ptr, 0, size)?;
                            Value::ByRef(ptr)
                        },
                        None => match this.ty_to_primval_kind(dest_ty) {
                            Ok(_) => Value::ByVal(PrimVal::Bytes(0)),
                            Err(_) => {
                                let ptr = this.alloc_ptr_with_substs(dest_ty, substs)?;
                                this.memory.write_repeat(ptr, 0, size)?;
                                Value::ByRef(ptr)
                            }
                        },
                        Some(Value::ByVal(_)) => Value::ByVal(PrimVal::Bytes(0)),
                        Some(Value::ByValPair(..)) =>
                            Value::ByValPair(PrimVal::Bytes(0), PrimVal::Bytes(0)),
                    };
                    Ok(Some(zero_val))
                };
                match dest {
                    Lvalue::Local { frame, local } => self.modify_local(frame, local, init)?,
                    Lvalue::Ptr { ptr, extra: LvalueExtra::None } => self.memory.write_repeat(ptr, 0, size)?,
                    Lvalue::Ptr { .. } => bug!("init intrinsic tried to write to fat ptr target"),
                    Lvalue::Global(cid) => self.modify_global(cid, init)?,
                }
            }

            "min_align_of" => {
                let elem_ty = substs.type_at(0);
                let elem_align = self.type_align(elem_ty)?;
                let align_val = PrimVal::from_u64(elem_align as u64);
                self.write_primval(dest, align_val, dest_ty)?;
            }

            "pref_align_of" => {
                let ty = substs.type_at(0);
                let layout = self.type_layout(ty)?;
                let align = layout.align(&self.tcx.data_layout).pref();
                let align_val = PrimVal::from_u64(align);
                self.write_primval(dest, align_val, dest_ty)?;
            }

            "move_val_init" => {
                let ty = substs.type_at(0);
                let ptr = arg_vals[0].read_ptr(&self.memory)?;
                self.write_value_to_ptr(arg_vals[1], ptr, ty)?;
            }

            "needs_drop" => {
                let ty = substs.type_at(0);
                let env = self.tcx.empty_parameter_environment();
                let needs_drop = self.tcx.type_needs_drop_given_env(ty, &env);
                self.write_primval(dest, PrimVal::from_bool(needs_drop), dest_ty)?;
            }

            "offset" => {
                let pointee_ty = substs.type_at(0);
                // FIXME: assuming here that type size is < i64::max_value()
                let pointee_size = self.type_size(pointee_ty)?.expect("cannot offset a pointer to an unsized type") as i64;
                let offset = self.value_to_primval(arg_vals[1], isize)?.to_i64()?;

                let ptr = arg_vals[0].read_ptr(&self.memory)?;
                let result_ptr = ptr.signed_offset(offset * pointee_size);
                self.write_primval(dest, PrimVal::Ptr(result_ptr), dest_ty)?;
            }

            "overflowing_sub" => {
                self.intrinsic_overflowing(mir::BinOp::Sub, &args[0], &args[1], dest, dest_ty)?;
            }

            "overflowing_mul" => {
                self.intrinsic_overflowing(mir::BinOp::Mul, &args[0], &args[1], dest, dest_ty)?;
            }

            "overflowing_add" => {
                self.intrinsic_overflowing(mir::BinOp::Add, &args[0], &args[1], dest, dest_ty)?;
            }

            "powif32" => {
                let f = self.value_to_primval(arg_vals[0], f32)?.to_f32()?;
                let i = self.value_to_primval(arg_vals[1], i32)?.to_i64()?;
                self.write_primval(dest, PrimVal::from_f32(f.powi(i as i32)), dest_ty)?;
            }

            "powif64" => {
                let f = self.value_to_primval(arg_vals[0], f64)?.to_f64()?;
                let i = self.value_to_primval(arg_vals[1], i32)?.to_i64()?;
                self.write_primval(dest, PrimVal::from_f64(f.powi(i as i32)), dest_ty)?;
            }

            "sqrtf32" => {
                let f = self.value_to_primval(arg_vals[0], f32)?.to_f32()?;
                self.write_primval(dest, PrimVal::from_f32(f.sqrt()), dest_ty)?;
            }

            "sqrtf64" => {
                let f = self.value_to_primval(arg_vals[0], f64)?.to_f64()?;
                self.write_primval(dest, PrimVal::from_f64(f.sqrt()), dest_ty)?;
            }

            "size_of" => {
                let ty = substs.type_at(0);
                // FIXME: change the `box_free` lang item to take `T: ?Sized` and have it use the
                // `size_of_val` intrinsic, then change this back to
                // .expect("size_of intrinsic called on unsized value")
                // see https://github.com/rust-lang/rust/pull/37708
                let size = self.type_size(ty)?.unwrap_or(!0) as u64;
                self.write_primval(dest, PrimVal::from_u64(size), dest_ty)?;
            }

            "size_of_val" => {
                let ty = substs.type_at(0);
                let (size, _) = self.size_and_align_of_dst(ty, arg_vals[0])?;
                self.write_primval(dest, PrimVal::from_u64(size), dest_ty)?;
            }

            "min_align_of_val" |
            "align_of_val" => {
                let ty = substs.type_at(0);
                let (_, align) = self.size_and_align_of_dst(ty, arg_vals[0])?;
                self.write_primval(dest, PrimVal::from_u64(align), dest_ty)?;
            }

            "type_name" => {
                let ty = substs.type_at(0);
                let ty_name = ty.to_string();
                let s = self.str_to_value(&ty_name)?;
                self.write_value(s, dest, dest_ty)?;
            }
            "type_id" => {
                let ty = substs.type_at(0);
                let n = self.tcx.type_id_hash(ty);
                self.write_primval(dest, PrimVal::Bytes(n), dest_ty)?;
            }

            "transmute" => {
                let dest_ty = substs.type_at(1);
                self.write_value(arg_vals[0], dest, dest_ty)?;
            }

            "uninit" => {
                let size = dest_layout.size(&self.tcx.data_layout).bytes();
                let uninit = |this: &mut Self, val: Option<Value>| {
                    match val {
                        Some(Value::ByRef(ptr)) => {
                            this.memory.mark_definedness(ptr, size, false)?;
                            Ok(Some(Value::ByRef(ptr)))
                        },
                        None => Ok(None),
                        Some(_) => Ok(None),
                    }
                };
                match dest {
                    Lvalue::Local { frame, local } => self.modify_local(frame, local, uninit)?,
                    Lvalue::Ptr { ptr, extra: LvalueExtra::None } => self.memory.mark_definedness(ptr, size, false)?,
                    Lvalue::Ptr { .. } => bug!("uninit intrinsic tried to write to fat ptr target"),
                    Lvalue::Global(cid) => self.modify_global(cid, uninit)?,
                }
            }

            name => return Err(EvalError::Unimplemented(format!("unimplemented intrinsic: {}", name))),
        }

        self.goto_block(target);

        // Since we pushed no stack frame, the main loop will act
        // as if the call just completed and it's returning to the
        // current frame.
        Ok(())
    }

    fn size_and_align_of_dst(
        &self,
        ty: ty::Ty<'tcx>,
        value: Value,
    ) -> EvalResult<'tcx, (u64, u64)> {
        let pointer_size = self.memory.pointer_size();
        if let Some(size) = self.type_size(ty)? {
            Ok((size as u64, self.type_align(ty)? as u64))
        } else {
            match ty.sty {
                ty::TyAdt(def, substs) => {
                    // First get the size of all statically known fields.
                    // Don't use type_of::sizing_type_of because that expects t to be sized,
                    // and it also rounds up to alignment, which we want to avoid,
                    // as the unsized field's alignment could be smaller.
                    assert!(!ty.is_simd());
                    let layout = self.type_layout(ty)?;
                    debug!("DST {} layout: {:?}", ty, layout);

                    let (sized_size, sized_align) = match *layout {
                        ty::layout::Layout::Univariant { ref variant, .. } => {
                            // The offset of the start of the last field gives the size of the
                            // sized part of the type.
                            let size = variant.offsets.last().map_or(0, |f| f.bytes());
                            (size, variant.align.abi())
                        }
                        _ => {
                            bug!("size_and_align_of_dst: expcted Univariant for `{}`, found {:#?}",
                                 ty, layout);
                        }
                    };
                    debug!("DST {} statically sized prefix size: {} align: {}",
                           ty, sized_size, sized_align);

                    // Recurse to get the size of the dynamically sized field (must be
                    // the last field).
                    let last_field = def.struct_variant().fields.last().unwrap();
                    let field_ty = self.field_ty(substs, last_field);
                    let (unsized_size, unsized_align) = self.size_and_align_of_dst(field_ty, value)?;

                    // FIXME (#26403, #27023): We should be adding padding
                    // to `sized_size` (to accommodate the `unsized_align`
                    // required of the unsized field that follows) before
                    // summing it with `sized_size`. (Note that since #26403
                    // is unfixed, we do not yet add the necessary padding
                    // here. But this is where the add would go.)

                    // Return the sum of sizes and max of aligns.
                    let size = sized_size + unsized_size;

                    // Choose max of two known alignments (combined value must
                    // be aligned according to more restrictive of the two).
                    let align = ::std::cmp::max(sized_align, unsized_align);

                    // Issue #27023: must add any necessary padding to `size`
                    // (to make it a multiple of `align`) before returning it.
                    //
                    // Namely, the returned size should be, in C notation:
                    //
                    //   `size + ((size & (align-1)) ? align : 0)`
                    //
                    // emulated via the semi-standard fast bit trick:
                    //
                    //   `(size + (align-1)) & -align`

                    if size & (align - 1) != 0 {
                        Ok((size + align, align))
                    } else {
                        Ok((size, align))
                    }
                }
                ty::TyDynamic(..) => {
                    let (_, vtable) = value.expect_ptr_vtable_pair(&self.memory)?;
                    // the second entry in the vtable is the dynamic size of the object.
                    let size = self.memory.read_usize(vtable.offset(pointer_size))?;
                    let align = self.memory.read_usize(vtable.offset(pointer_size * 2))?;
                    Ok((size, align))
                }

                ty::TySlice(_) | ty::TyStr => {
                    let elem_ty = ty.sequence_element_type(self.tcx);
                    let elem_size = self.type_size(elem_ty)?.expect("slice element must be sized") as u64;
                    let (_, len) = value.expect_slice(&self.memory)?;
                    let align = self.type_align(elem_ty)?;
                    Ok((len * elem_size, align as u64))
                }

                _ => bug!("size_of_val::<{:?}>", ty),
            }
        }
    }
    /// Returns the normalized type of a struct field
    fn field_ty(
        &self,
        param_substs: &Substs<'tcx>,
        f: &ty::FieldDef,
    ) -> ty::Ty<'tcx> {
        self.tcx.normalize_associated_type(&f.ty(self.tcx, param_substs))
    }
}

fn numeric_intrinsic<'tcx>(
    name: &str,
    val: PrimVal,
    kind: PrimValKind
) -> EvalResult<'tcx, PrimVal> {
    macro_rules! integer_intrinsic {
        ($name:expr, $val:expr, $kind:expr, $method:ident) => ({
            let val = $val;
            let bytes = val.to_bytes()?;

            use value::PrimValKind::*;
            let result_bytes = match $kind {
                I8 => (bytes as i8).$method() as u64,
                U8 => (bytes as u8).$method() as u64,
                I16 => (bytes as i16).$method() as u64,
                U16 => (bytes as u16).$method() as u64,
                I32 => (bytes as i32).$method() as u64,
                U32 => (bytes as u32).$method() as u64,
                I64 => (bytes as i64).$method() as u64,
                U64 => bytes.$method() as u64,
                _ => bug!("invalid `{}` argument: {:?}", $name, val),
            };

            PrimVal::Bytes(result_bytes)
        });
    }

    let result_val = match name {
        "bswap" => integer_intrinsic!("bswap", val, kind, swap_bytes),
        "ctlz"  => integer_intrinsic!("ctlz",  val, kind, leading_zeros),
        "ctpop" => integer_intrinsic!("ctpop", val, kind, count_ones),
        "cttz"  => integer_intrinsic!("cttz",  val, kind, trailing_zeros),
        _       => bug!("not a numeric intrinsic: {}", name),
    };

    Ok(result_val)
}