compiler/rustc_const_eval/src/interpret/step.rs - toolchain/rustc - Git at Google

 //! This module contains the `InterpCx` methods for executing a single step of the interpreter.
 //!
 //! The main entry point is the `step` method.

 use either::Either;

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

 use super::{ImmTy, InterpCx, Machine, Projectable};
 use crate::util;

 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     /// Returns `true` as long as there are more things to do.
     ///
     /// This is used by [priroda](https://github.com/oli-obk/priroda)
     ///
     /// This is marked `#inline(always)` to work around adversarial codegen when `opt-level = 3`
     #[inline(always)]
     pub fn step(&mut self) -> InterpResult<'tcx, bool> {
         if self.stack().is_empty() {
             return Ok(false);
         }

         let Either::Left(loc) = self.frame().loc else {
             // We are unwinding and this fn has no cleanup code.
             // Just go on unwinding.
             trace!("unwinding: skipping frame");
             self.pop_stack_frame(/* unwinding */ true)?;
             return Ok(true);
         };
         let basic_block = &self.body().basic_blocks[loc.block];

         if let Some(stmt) = basic_block.statements.get(loc.statement_index) {
             let old_frames = self.frame_idx();
             self.statement(stmt)?;
             // Make sure we are not updating `statement_index` of the wrong frame.
             assert_eq!(old_frames, self.frame_idx());
             // Advance the program counter.
             self.frame_mut().loc.as_mut().left().unwrap().statement_index += 1;
             return Ok(true);
         }

         M::before_terminator(self)?;

         let terminator = basic_block.terminator();
         self.terminator(terminator)?;
         Ok(true)
     }

     /// Runs the interpretation logic for the given `mir::Statement` at the current frame and
     /// statement counter.
     ///
     /// This does NOT move the statement counter forward, the caller has to do that!
     pub fn statement(&mut self, stmt: &mir::Statement<'tcx>) -> InterpResult<'tcx> {
         info!("{:?}", stmt);

         use rustc_middle::mir::StatementKind::*;

         match &stmt.kind {
             Assign(box (place, rvalue)) => self.eval_rvalue_into_place(rvalue, *place)?,

             SetDiscriminant { place, variant_index } => {
                 let dest = self.eval_place(**place)?;
                 self.write_discriminant(*variant_index, &dest)?;
             }

             Deinit(place) => {
                 let dest = self.eval_place(**place)?;
                 self.write_uninit(&dest)?;
             }

             // Mark locals as alive
             StorageLive(local) => {
                 self.storage_live(*local)?;
             }

             // Mark locals as dead
             StorageDead(local) => {
                 self.storage_dead(*local)?;
             }

             // No dynamic semantics attached to `FakeRead`; MIR
             // interpreter is solely intended for borrowck'ed code.
             FakeRead(..) => {}

             // Stacked Borrows.
             Retag(kind, place) => {
                 let dest = self.eval_place(**place)?;
                 M::retag_place_contents(self, *kind, &dest)?;
             }

             Intrinsic(box intrinsic) => self.emulate_nondiverging_intrinsic(intrinsic)?,

             // Evaluate the place expression, without reading from it.
             PlaceMention(box place) => {
                 let _ = self.eval_place(*place)?;
             }

             // This exists purely to guide borrowck lifetime inference, and does not have
             // an operational effect.
             AscribeUserType(..) => {}

             // Currently, Miri discards Coverage statements. Coverage statements are only injected
             // via an optional compile time MIR pass and have no side effects. Since Coverage
             // statements don't exist at the source level, it is safe for Miri to ignore them, even
             // for undefined behavior (UB) checks.
             //
             // A coverage counter inside a const expression (for example, a counter injected in a
             // const function) is discarded when the const is evaluated at compile time. Whether
             // this should change, and/or how to implement a const eval counter, is a subject of the
             // following issue:
             //
             // FIXME(#73156): Handle source code coverage in const eval
             Coverage(..) => {}

             ConstEvalCounter => {
                 M::increment_const_eval_counter(self)?;
             }

             // Defined to do nothing. These are added by optimization passes, to avoid changing the
             // size of MIR constantly.
             Nop => {}
         }

         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.
     pub fn eval_rvalue_into_place(
         &mut self,
         rvalue: &mir::Rvalue<'tcx>,
         place: mir::Place<'tcx>,
     ) -> InterpResult<'tcx> {
         let dest = self.eval_place(place)?;
         // FIXME: ensure some kind of non-aliasing between LHS and RHS?
         // Also see https://github.com/rust-lang/rust/issues/68364.

         use rustc_middle::mir::Rvalue::*;
         match *rvalue {
             ThreadLocalRef(did) => {
                 let ptr = M::thread_local_static_base_pointer(self, did)?;
                 self.write_pointer(ptr, &dest)?;
             }

             Use(ref operand) => {
                 // Avoid recomputing the layout
                 let op = self.eval_operand(operand, Some(dest.layout))?;
                 self.copy_op(&op, &dest, /*allow_transmute*/ false)?;
             }

             CopyForDeref(place) => {
                 let op = self.eval_place_to_op(place, Some(dest.layout))?;
                 self.copy_op(&op, &dest, /* allow_transmute*/ false)?;
             }

             BinaryOp(bin_op, box (ref left, ref right)) => {
                 let layout = util::binop_left_homogeneous(bin_op).then_some(dest.layout);
                 let left = self.read_immediate(&self.eval_operand(left, layout)?)?;
                 let layout = util::binop_right_homogeneous(bin_op).then_some(left.layout);
                 let right = self.read_immediate(&self.eval_operand(right, layout)?)?;
                 self.binop_ignore_overflow(bin_op, &left, &right, &dest)?;
             }

             CheckedBinaryOp(bin_op, box (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 = util::binop_right_homogeneous(bin_op).then_some(left.layout);
                 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.wrapping_unary_op(un_op, &val)?;
                 assert_eq!(val.layout, dest.layout, "layout mismatch for result of {un_op:?}");
                 self.write_immediate(*val, &dest)?;
             }

             Aggregate(box ref kind, ref operands) => {
                 self.write_aggregate(kind, operands, &dest)?;
             }

             Repeat(ref operand, _) => {
                 let src = self.eval_operand(operand, None)?;
                 assert!(src.layout.is_sized());
                 let dest = self.force_allocation(&dest)?;
                 let length = dest.len(self)?;

                 if length == 0 {
                     // Nothing to copy... but let's still make sure that `dest` as a place is valid.
                     self.get_place_alloc_mut(&dest)?;
                 } else {
                     // Write the src to the first element.
                     let first = self.project_index(&dest, 0)?;
                     self.copy_op(&src, &first, /*allow_transmute*/ false)?;

                     // This is performance-sensitive code for big static/const arrays! So we
                     // avoid writing each operand individually and instead just make many copies
                     // of the first element.
                     let elem_size = first.layout.size;
                     let first_ptr = first.ptr();
                     let rest_ptr = first_ptr.offset(elem_size, self)?;
                     // No alignment requirement since `copy_op` above already checked it.
                     self.mem_copy_repeatedly(
                         first_ptr,
                         rest_ptr,
                         elem_size,
                         length - 1,
                         /*nonoverlapping:*/ true,
                     )?;
                 }
             }

             Len(place) => {
                 let src = self.eval_place(place)?;
                 let len = src.len(self)?;
                 self.write_scalar(Scalar::from_target_usize(len, self), &dest)?;
             }

             Ref(_, borrow_kind, place) => {
                 let src = self.eval_place(place)?;
                 let place = self.force_allocation(&src)?;
                 let val = ImmTy::from_immediate(place.to_ref(self), dest.layout);
                 // A fresh reference was created, make sure it gets retagged.
                 let val = M::retag_ptr_value(
                     self,
                     if borrow_kind.allows_two_phase_borrow() {
                         mir::RetagKind::TwoPhase
                     } else {
                         mir::RetagKind::Default
                     },
                     &val,
                 )?;
                 self.write_immediate(*val, &dest)?;
             }

             AddressOf(_, place) => {
                 // Figure out whether this is an addr_of of an already raw place.
                 let place_base_raw = if place.is_indirect_first_projection() {
                     let ty = self.frame().body.local_decls[place.local].ty;
                     ty.is_unsafe_ptr()
                 } else {
                     // Not a deref, and thus not raw.
                     false
                 };

                 let src = self.eval_place(place)?;
                 let place = self.force_allocation(&src)?;
                 let mut val = ImmTy::from_immediate(place.to_ref(self), dest.layout);
                 if !place_base_raw {
                     // If this was not already raw, it needs retagging.
                     val = M::retag_ptr_value(self, mir::RetagKind::Raw, &val)?;
                 }
                 self.write_immediate(*val, &dest)?;
             }

             NullaryOp(ref null_op, ty) => {
                 let ty = self.subst_from_current_frame_and_normalize_erasing_regions(ty)?;
                 let layout = self.layout_of(ty)?;
                 if let mir::NullOp::SizeOf | mir::NullOp::AlignOf = null_op
                     && layout.is_unsized()
                 {
                     span_bug!(
                         self.frame().current_span(),
                         "{null_op:?} MIR operator called for unsized type {ty}",
                     );
                 }
                 let val = match null_op {
                     mir::NullOp::SizeOf => layout.size.bytes(),
                     mir::NullOp::AlignOf => layout.align.abi.bytes(),
                     mir::NullOp::OffsetOf(fields) => {
                         layout.offset_of_subfield(self, fields.iter()).bytes()
                     }
                 };
                 self.write_scalar(Scalar::from_target_usize(val, self), &dest)?;
             }

             ShallowInitBox(ref operand, _) => {
                 let src = self.eval_operand(operand, None)?;
                 let v = self.read_immediate(&src)?;
                 self.write_immediate(*v, &dest)?;
             }

             Cast(cast_kind, ref operand, cast_ty) => {
                 let src = self.eval_operand(operand, None)?;
                 let cast_ty =
                     self.subst_from_current_frame_and_normalize_erasing_regions(cast_ty)?;
                 self.cast(&src, cast_kind, cast_ty, &dest)?;
             }

             Discriminant(place) => {
                 let op = self.eval_place_to_op(place, None)?;
                 let variant = self.read_discriminant(&op)?;
                 let discr = self.discriminant_for_variant(op.layout.ty, variant)?;
                 self.write_immediate(*discr, &dest)?;
             }
         }

         trace!("{:?}", self.dump_place(&dest));

         Ok(())
     }

     /// Evaluate the given terminator. Will also adjust the stack frame and statement position accordingly.
     fn terminator(&mut self, terminator: &mir::Terminator<'tcx>) -> InterpResult<'tcx> {
         info!("{:?}", terminator.kind);

         self.eval_terminator(terminator)?;
         if !self.stack().is_empty() {
             if let Either::Left(loc) = self.frame().loc {
                 info!("// executing {:?}", loc.block);
             }
         }
         Ok(())
     }
 }
	//! This module contains the `InterpCx` methods for executing a single step of the interpreter.
	//!
	//! The main entry point is the `step` method.

	use either::Either;

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

	use super::{ImmTy, InterpCx, Machine, Projectable};
	use crate::util;

	impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
	/// Returns `true` as long as there are more things to do.
	///
	/// This is used by [priroda](https://github.com/oli-obk/priroda)
	///
	/// This is marked `#inline(always)` to work around adversarial codegen when `opt-level = 3`
	#[inline(always)]
	pub fn step(&mut self) -> InterpResult<'tcx, bool> {
	if self.stack().is_empty() {
	return Ok(false);
	}

	let Either::Left(loc) = self.frame().loc else {
	// We are unwinding and this fn has no cleanup code.
	// Just go on unwinding.
	trace!("unwinding: skipping frame");
	self.pop_stack_frame(/* unwinding */ true)?;
	return Ok(true);
	};
	let basic_block = &self.body().basic_blocks[loc.block];

	if let Some(stmt) = basic_block.statements.get(loc.statement_index) {
	let old_frames = self.frame_idx();
	self.statement(stmt)?;
	// Make sure we are not updating `statement_index` of the wrong frame.
	assert_eq!(old_frames, self.frame_idx());
	// Advance the program counter.
	self.frame_mut().loc.as_mut().left().unwrap().statement_index += 1;
	return Ok(true);
	}

	M::before_terminator(self)?;

	let terminator = basic_block.terminator();
	self.terminator(terminator)?;
	Ok(true)
	}

	/// Runs the interpretation logic for the given `mir::Statement` at the current frame and
	/// statement counter.
	///
	/// This does NOT move the statement counter forward, the caller has to do that!
	pub fn statement(&mut self, stmt: &mir::Statement<'tcx>) -> InterpResult<'tcx> {
	info!("{:?}", stmt);

	use rustc_middle::mir::StatementKind::*;

	match &stmt.kind {
	Assign(box (place, rvalue)) => self.eval_rvalue_into_place(rvalue, *place)?,

	SetDiscriminant { place, variant_index } => {
	let dest = self.eval_place(**place)?;
	self.write_discriminant(*variant_index, &dest)?;
	}

	Deinit(place) => {
	let dest = self.eval_place(**place)?;
	self.write_uninit(&dest)?;
	}

	// Mark locals as alive
	StorageLive(local) => {
	self.storage_live(*local)?;
	}

	// Mark locals as dead
	StorageDead(local) => {
	self.storage_dead(*local)?;
	}

	// No dynamic semantics attached to `FakeRead`; MIR
	// interpreter is solely intended for borrowck'ed code.
	FakeRead(..) => {}

	// Stacked Borrows.
	Retag(kind, place) => {
	let dest = self.eval_place(**place)?;
	M::retag_place_contents(self, *kind, &dest)?;
	}

	Intrinsic(box intrinsic) => self.emulate_nondiverging_intrinsic(intrinsic)?,

	// Evaluate the place expression, without reading from it.
	PlaceMention(box place) => {
	let _ = self.eval_place(*place)?;
	}

	// This exists purely to guide borrowck lifetime inference, and does not have
	// an operational effect.
	AscribeUserType(..) => {}

	// Currently, Miri discards Coverage statements. Coverage statements are only injected
	// via an optional compile time MIR pass and have no side effects. Since Coverage
	// statements don't exist at the source level, it is safe for Miri to ignore them, even
	// for undefined behavior (UB) checks.
	//
	// A coverage counter inside a const expression (for example, a counter injected in a
	// const function) is discarded when the const is evaluated at compile time. Whether
	// this should change, and/or how to implement a const eval counter, is a subject of the
	// following issue:
	//
	// FIXME(#73156): Handle source code coverage in const eval
	Coverage(..) => {}

	ConstEvalCounter => {
	M::increment_const_eval_counter(self)?;
	}

	// Defined to do nothing. These are added by optimization passes, to avoid changing the
	// size of MIR constantly.
	Nop => {}
	}

	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.
	pub fn eval_rvalue_into_place(
	&mut self,
	rvalue: &mir::Rvalue<'tcx>,
	place: mir::Place<'tcx>,
	) -> InterpResult<'tcx> {
	let dest = self.eval_place(place)?;
	// FIXME: ensure some kind of non-aliasing between LHS and RHS?
	// Also see https://github.com/rust-lang/rust/issues/68364.

	use rustc_middle::mir::Rvalue::*;
	match *rvalue {
	ThreadLocalRef(did) => {
	let ptr = M::thread_local_static_base_pointer(self, did)?;
	self.write_pointer(ptr, &dest)?;
	}

	Use(ref operand) => {
	// Avoid recomputing the layout
	let op = self.eval_operand(operand, Some(dest.layout))?;
	self.copy_op(&op, &dest, /allow_transmute/ false)?;
	}

	CopyForDeref(place) => {
	let op = self.eval_place_to_op(place, Some(dest.layout))?;
	self.copy_op(&op, &dest, /* allow_transmute*/ false)?;
	}

	BinaryOp(bin_op, box (ref left, ref right)) => {
	let layout = util::binop_left_homogeneous(bin_op).then_some(dest.layout);
	let left = self.read_immediate(&self.eval_operand(left, layout)?)?;
	let layout = util::binop_right_homogeneous(bin_op).then_some(left.layout);
	let right = self.read_immediate(&self.eval_operand(right, layout)?)?;
	self.binop_ignore_overflow(bin_op, &left, &right, &dest)?;
	}

	CheckedBinaryOp(bin_op, box (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 = util::binop_right_homogeneous(bin_op).then_some(left.layout);
	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.wrapping_unary_op(un_op, &val)?;
	assert_eq!(val.layout, dest.layout, "layout mismatch for result of {un_op:?}");
	self.write_immediate(*val, &dest)?;
	}

	Aggregate(box ref kind, ref operands) => {
	self.write_aggregate(kind, operands, &dest)?;
	}

	Repeat(ref operand, _) => {
	let src = self.eval_operand(operand, None)?;
	assert!(src.layout.is_sized());
	let dest = self.force_allocation(&dest)?;
	let length = dest.len(self)?;

	if length == 0 {
	// Nothing to copy... but let's still make sure that `dest` as a place is valid.
	self.get_place_alloc_mut(&dest)?;
	} else {
	// Write the src to the first element.
	let first = self.project_index(&dest, 0)?;
	self.copy_op(&src, &first, /allow_transmute/ false)?;

	// This is performance-sensitive code for big static/const arrays! So we
	// avoid writing each operand individually and instead just make many copies
	// of the first element.
	let elem_size = first.layout.size;
	let first_ptr = first.ptr();
	let rest_ptr = first_ptr.offset(elem_size, self)?;
	// No alignment requirement since `copy_op` above already checked it.
	self.mem_copy_repeatedly(
	first_ptr,
	rest_ptr,
	elem_size,
	length - 1,
	/nonoverlapping:/ true,
	)?;
	}
	}

	Len(place) => {
	let src = self.eval_place(place)?;
	let len = src.len(self)?;
	self.write_scalar(Scalar::from_target_usize(len, self), &dest)?;
	}

	Ref(_, borrow_kind, place) => {
	let src = self.eval_place(place)?;
	let place = self.force_allocation(&src)?;
	let val = ImmTy::from_immediate(place.to_ref(self), dest.layout);
	// A fresh reference was created, make sure it gets retagged.
	let val = M::retag_ptr_value(
	self,
	if borrow_kind.allows_two_phase_borrow() {
	mir::RetagKind::TwoPhase
	} else {
	mir::RetagKind::Default
	},
	&val,
	)?;
	self.write_immediate(*val, &dest)?;
	}

	AddressOf(_, place) => {
	// Figure out whether this is an addr_of of an already raw place.
	let place_base_raw = if place.is_indirect_first_projection() {
	let ty = self.frame().body.local_decls[place.local].ty;
	ty.is_unsafe_ptr()
	} else {
	// Not a deref, and thus not raw.
	false
	};

	let src = self.eval_place(place)?;
	let place = self.force_allocation(&src)?;
	let mut val = ImmTy::from_immediate(place.to_ref(self), dest.layout);
	if !place_base_raw {
	// If this was not already raw, it needs retagging.
	val = M::retag_ptr_value(self, mir::RetagKind::Raw, &val)?;
	}
	self.write_immediate(*val, &dest)?;
	}

	NullaryOp(ref null_op, ty) => {
	let ty = self.subst_from_current_frame_and_normalize_erasing_regions(ty)?;
	let layout = self.layout_of(ty)?;
	if let mir::NullOp::SizeOf \| mir::NullOp::AlignOf = null_op
	&& layout.is_unsized()
	{
	span_bug!(
	self.frame().current_span(),
	"{null_op:?} MIR operator called for unsized type {ty}",
	);
	}
	let val = match null_op {
	mir::NullOp::SizeOf => layout.size.bytes(),
	mir::NullOp::AlignOf => layout.align.abi.bytes(),
	mir::NullOp::OffsetOf(fields) => {
	layout.offset_of_subfield(self, fields.iter()).bytes()
	}
	};
	self.write_scalar(Scalar::from_target_usize(val, self), &dest)?;
	}

	ShallowInitBox(ref operand, _) => {
	let src = self.eval_operand(operand, None)?;
	let v = self.read_immediate(&src)?;
	self.write_immediate(*v, &dest)?;
	}

	Cast(cast_kind, ref operand, cast_ty) => {
	let src = self.eval_operand(operand, None)?;
	let cast_ty =
	self.subst_from_current_frame_and_normalize_erasing_regions(cast_ty)?;
	self.cast(&src, cast_kind, cast_ty, &dest)?;
	}

	Discriminant(place) => {
	let op = self.eval_place_to_op(place, None)?;
	let variant = self.read_discriminant(&op)?;
	let discr = self.discriminant_for_variant(op.layout.ty, variant)?;
	self.write_immediate(*discr, &dest)?;
	}
	}

	trace!("{:?}", self.dump_place(&dest));

	Ok(())
	}

	/// Evaluate the given terminator. Will also adjust the stack frame and statement position accordingly.
	fn terminator(&mut self, terminator: &mir::Terminator<'tcx>) -> InterpResult<'tcx> {
	info!("{:?}", terminator.kind);

	self.eval_terminator(terminator)?;
	if !self.stack().is_empty() {
	if let Either::Left(loc) = self.frame().loc {
	info!("// executing {:?}", loc.block);
	}
	}
	Ok(())
	}
	}