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//! This module contains the `InterpCx` methods for executing a single step of the interpreter.
//!
//! The main entry point is the `step` method.
use rustc::mir;
use rustc::ty::layout::LayoutOf;
use rustc::mir::interpret::{InterpResult, Scalar, PointerArithmetic};
use super::{InterpCx, Machine};
/// Classify whether an operator is "left-homogeneous", i.e., the LHS has the
/// same type as the result.
#[inline]
fn binop_left_homogeneous(op: mir::BinOp) -> bool {
use rustc::mir::BinOp::*;
match op {
Add | Sub | Mul | Div | Rem | BitXor | BitAnd | BitOr |
Offset | Shl | Shr =>
true,
Eq | Ne | Lt | Le | Gt | Ge =>
false,
}
}
/// Classify whether an operator is "right-homogeneous", i.e., the RHS has the
/// same type as the LHS.
#[inline]
fn binop_right_homogeneous(op: mir::BinOp) -> bool {
use rustc::mir::BinOp::*;
match op {
Add | Sub | Mul | Div | Rem | BitXor | BitAnd | BitOr |
Eq | Ne | Lt | Le | Gt | Ge =>
true,
Offset | Shl | Shr =>
false,
}
}
impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
pub fn run(&mut self) -> InterpResult<'tcx> {
while self.step()? {}
Ok(())
}
/// Returns `true` as long as there are more things to do.
///
/// This is used by [priroda](https://github.com/oli-obk/priroda)
pub fn step(&mut self) -> InterpResult<'tcx, bool> {
if self.stack.is_empty() {
return Ok(false);
}
let block = self.frame().block;
let stmt_id = self.frame().stmt;
let body = self.body();
let basic_block = &body.basic_blocks()[block];
let old_frames = self.cur_frame();
if let Some(stmt) = basic_block.statements.get(stmt_id) {
assert_eq!(old_frames, self.cur_frame());
self.statement(stmt)?;
return Ok(true);
}
M::before_terminator(self)?;
let terminator = basic_block.terminator();
assert_eq!(old_frames, self.cur_frame());
self.terminator(terminator)?;
Ok(true)
}
fn statement(&mut self, stmt: &mir::Statement<'tcx>) -> InterpResult<'tcx> {
info!("{:?}", stmt);
use rustc::mir::StatementKind::*;
// Some statements (e.g., box) push new stack frames.
// We have to record the stack frame number *before* executing the statement.
let frame_idx = self.cur_frame();
self.tcx.span = stmt.source_info.span;
self.memory.tcx.span = stmt.source_info.span;
match stmt.kind {
Assign(ref place, ref rvalue) => self.eval_rvalue_into_place(rvalue, place)?,
SetDiscriminant {
ref place,
variant_index,
} => {
let dest = self.eval_place(place)?;
self.write_discriminant_index(variant_index, dest)?;
}
// Mark locals as alive
StorageLive(local) => {
let old_val = self.storage_live(local)?;
self.deallocate_local(old_val)?;
}
// Mark locals as dead
StorageDead(local) => {
let old_val = self.storage_dead(local);
self.deallocate_local(old_val)?;
}
// No dynamic semantics attached to `FakeRead`; MIR
// interpreter is solely intended for borrowck'ed code.
FakeRead(..) => {}
// Stacked Borrows.
Retag(kind, ref place) => {
let dest = self.eval_place(place)?;
M::retag(self, kind, dest)?;
}
// Statements we do not track.
AscribeUserType(..) => {}
// Defined to do nothing. These are added by optimization passes, to avoid changing the
// size of MIR constantly.
Nop => {}
InlineAsm { .. } => return err!(InlineAsm),
}
self.stack[frame_idx].stmt += 1;
Ok(())
}
/// Evaluate an assignment statement.
///
/// There is no separate `eval_rvalue` function. Instead, the code for handling each rvalue
/// type writes its results directly into the memory specified by the place.
fn eval_rvalue_into_place(
&mut self,
rvalue: &mir::Rvalue<'tcx>,
place: &mir::Place<'tcx>,
) -> InterpResult<'tcx> {
let dest = self.eval_place(place)?;
use rustc::mir::Rvalue::*;
match *rvalue {
Use(ref operand) => {
// Avoid recomputing the layout
let op = self.eval_operand(operand, Some(dest.layout))?;
self.copy_op(op, dest)?;
}
BinaryOp(bin_op, ref left, ref right) => {
let layout = if binop_left_homogeneous(bin_op) { Some(dest.layout) } else { None };
let left = self.read_immediate(self.eval_operand(left, layout)?)?;
let layout = if binop_right_homogeneous(bin_op) { Some(left.layout) } else { None };
let right = self.read_immediate(self.eval_operand(right, layout)?)?;
self.binop_ignore_overflow(
bin_op,
left,
right,
dest,
)?;
}
CheckedBinaryOp(bin_op, ref left, ref right) => {
// Due to the extra boolean in the result, we can never reuse the `dest.layout`.
let left = self.read_immediate(self.eval_operand(left, None)?)?;
let layout = if binop_right_homogeneous(bin_op) { Some(left.layout) } else { None };
let right = self.read_immediate(self.eval_operand(right, layout)?)?;
self.binop_with_overflow(
bin_op,
left,
right,
dest,
)?;
}
UnaryOp(un_op, ref operand) => {
// The operand always has the same type as the result.
let val = self.read_immediate(self.eval_operand(operand, Some(dest.layout))?)?;
let val = self.unary_op(un_op, val)?;
self.write_scalar(val, dest)?;
}
Aggregate(ref kind, ref operands) => {
let (dest, active_field_index) = match **kind {
mir::AggregateKind::Adt(adt_def, variant_index, _, _, active_field_index) => {
self.write_discriminant_index(variant_index, dest)?;
if adt_def.is_enum() {
(self.place_downcast(dest, variant_index)?, active_field_index)
} else {
(dest, active_field_index)
}
}
_ => (dest, None)
};
for (i, operand) in operands.iter().enumerate() {
let op = self.eval_operand(operand, None)?;
// Ignore zero-sized fields.
if !op.layout.is_zst() {
let field_index = active_field_index.unwrap_or(i);
let field_dest = self.place_field(dest, field_index as u64)?;
self.copy_op(op, field_dest)?;
}
}
}
Repeat(ref operand, _) => {
let op = self.eval_operand(operand, None)?;
let dest = self.force_allocation(dest)?;
let length = dest.len(self)?;
if let Some(first_ptr) = self.check_mplace_access(dest, None)? {
// Write the first.
let first = self.mplace_field(dest, 0)?;
self.copy_op(op, first.into())?;
if length > 1 {
let elem_size = first.layout.size;
// Copy the rest. This is performance-sensitive code
// for big static/const arrays!
let rest_ptr = first_ptr.offset(elem_size, self)?;
self.memory.copy_repeatedly(
first_ptr, rest_ptr, elem_size, length - 1, /*nonoverlapping:*/true
)?;
}
}
}
Len(ref place) => {
// FIXME(CTFE): don't allow computing the length of arrays in const eval
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,
)?;
}
Ref(_, _, ref place) => {
let src = self.eval_place(place)?;
let val = self.force_allocation(src)?;
self.write_immediate(val.to_ref(), dest)?;
}
NullaryOp(mir::NullOp::Box, _) => {
M::box_alloc(self, dest)?;
}
NullaryOp(mir::NullOp::SizeOf, ty) => {
let ty = self.monomorphize(ty)?;
let layout = self.layout_of(ty)?;
assert!(!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,
)?;
}
Cast(kind, ref operand, _) => {
let src = self.eval_operand(operand, None)?;
self.cast(src, kind, dest)?;
}
Discriminant(ref place) => {
let op = self.eval_place_to_op(place, None)?;
let discr_val = self.read_discriminant(op)?.0;
let size = dest.layout.size;
self.write_scalar(Scalar::from_uint(discr_val, size), dest)?;
}
}
self.dump_place(*dest);
Ok(())
}
fn terminator(&mut self, terminator: &mir::Terminator<'tcx>) -> InterpResult<'tcx> {
info!("{:?}", terminator.kind);
self.tcx.span = terminator.source_info.span;
self.memory.tcx.span = terminator.source_info.span;
let old_stack = self.cur_frame();
let old_bb = self.frame().block;
self.eval_terminator(terminator)?;
if !self.stack.is_empty() {
// This should change *something*
debug_assert!(self.cur_frame() != old_stack || self.frame().block != old_bb);
info!("// {:?}", self.frame().block);
}
Ok(())
}
}
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