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interpret: refactor function call handling to be better-abstracted

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This commit is contained in:
Ralf Jung
2024-08-05 17:34:44 +02:00
parent 8c7e0e1608
commit 522af10ccc
22 changed files with 1337 additions and 1316 deletions
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638
compiler/rustc_const_eval/src/interpret/stack.rs Normal file
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//! Manages the low-level pushing and popping of stack frames and the (de)allocation of local variables.
//! For hadling of argument passing and return values, see the `call` module.
use std::cell::Cell;
use std::{fmt, mem};
use either::{Either, Left, Right};
use rustc_hir as hir;
use rustc_hir::definitions::DefPathData;
use rustc_index::IndexVec;
use rustc_middle::ty::layout::{LayoutOf, TyAndLayout};
use rustc_middle::ty::{self, Ty, TyCtxt};
use rustc_middle::{bug, mir};
use rustc_mir_dataflow::storage::always_storage_live_locals;
use rustc_span::Span;
use tracing::{info_span, instrument, trace};
use super::{
from_known_layout, throw_ub, throw_unsup, AllocId, CtfeProvenance, Immediate, InterpCx,
InterpResult, MPlaceTy, Machine, MemPlace, MemPlaceMeta, MemoryKind, Operand, Pointer,
Provenance, ReturnAction, Scalar,
};
use crate::errors;
// The Phantomdata exists to prevent this type from being `Send`. If it were sent across a thread
// boundary and dropped in the other thread, it would exit the span in the other thread.
struct SpanGuard(tracing::Span, std::marker::PhantomData<*const u8>);
impl SpanGuard {
/// By default a `SpanGuard` does nothing.
fn new() -> Self {
Self(tracing::Span::none(), std::marker::PhantomData)
}
/// If a span is entered, we exit the previous span (if any, normally none) and enter the
/// new span. This is mainly so we don't have to use `Option` for the `tracing_span` field of
/// `Frame` by creating a dummy span to being with and then entering it once the frame has
/// been pushed.
fn enter(&mut self, span: tracing::Span) {
// This executes the destructor on the previous instance of `SpanGuard`, ensuring that
// we never enter or exit more spans than vice versa. Unless you `mem::leak`, then we
// can't protect the tracing stack, but that'll just lead to weird logging, no actual
// problems.
*self = Self(span, std::marker::PhantomData);
self.0.with_subscriber(|(id, dispatch)| {
dispatch.enter(id);
});
}
}
impl Drop for SpanGuard {
fn drop(&mut self) {
self.0.with_subscriber(|(id, dispatch)| {
dispatch.exit(id);
});
}
}
/// A stack frame.
pub struct Frame<'tcx, Prov: Provenance = CtfeProvenance, Extra = ()> {
////////////////////////////////////////////////////////////////////////////////
// Function and callsite information
////////////////////////////////////////////////////////////////////////////////
/// The MIR for the function called on this frame.
pub body: &'tcx mir::Body<'tcx>,
/// The def_id and args of the current function.
pub instance: ty::Instance<'tcx>,
/// Extra data for the machine.
pub extra: Extra,
////////////////////////////////////////////////////////////////////////////////
// Return place and locals
////////////////////////////////////////////////////////////////////////////////
/// Work to perform when returning from this function.
pub return_to_block: StackPopCleanup,
/// The location where the result of the current stack frame should be written to,
/// and its layout in the caller.
pub return_place: MPlaceTy<'tcx, Prov>,
/// The list of locals for this stack frame, stored in order as
/// `[return_ptr, arguments..., variables..., temporaries...]`.
/// The locals are stored as `Option<Value>`s.
/// `None` represents a local that is currently dead, while a live local
/// can either directly contain `Scalar` or refer to some part of an `Allocation`.
///
/// Do *not* access this directly; always go through the machine hook!
pub locals: IndexVec<mir::Local, LocalState<'tcx, Prov>>,
/// The span of the `tracing` crate is stored here.
/// When the guard is dropped, the span is exited. This gives us
/// a full stack trace on all tracing statements.
tracing_span: SpanGuard,
////////////////////////////////////////////////////////////////////////////////
// Current position within the function
////////////////////////////////////////////////////////////////////////////////
/// If this is `Right`, we are not currently executing any particular statement in
/// this frame (can happen e.g. during frame initialization, and during unwinding on
/// frames without cleanup code).
///
/// Needs to be public because ConstProp does unspeakable things to it.
pub loc: Either<mir::Location, Span>,
}
#[derive(Clone, Copy, Eq, PartialEq, Debug)] // Miri debug-prints these
pub enum StackPopCleanup {
/// Jump to the next block in the caller, or cause UB if None (that's a function
/// that may never return). Also store layout of return place so
/// we can validate it at that layout.
/// `ret` stores the block we jump to on a normal return, while `unwind`
/// stores the block used for cleanup during unwinding.
Goto { ret: Option<mir::BasicBlock>, unwind: mir::UnwindAction },
/// The root frame of the stack: nowhere else to jump to.
/// `cleanup` says whether locals are deallocated. Static computation
/// wants them leaked to intern what they need (and just throw away
/// the entire `ecx` when it is done).
Root { cleanup: bool },
}
/// Return type of [`InterpCx::pop_stack_frame_raw`].
pub struct StackPopInfo<'tcx, Prov: Provenance> {
/// Additional information about the action to be performed when returning from the popped
/// stack frame.
pub return_action: ReturnAction,
/// [`return_to_block`](Frame::return_to_block) of the popped stack frame.
pub return_to_block: StackPopCleanup,
/// [`return_place`](Frame::return_place) of the popped stack frame.
pub return_place: MPlaceTy<'tcx, Prov>,
}
/// State of a local variable including a memoized layout
#[derive(Clone)]
pub struct LocalState<'tcx, Prov: Provenance = CtfeProvenance> {
value: LocalValue<Prov>,
/// Don't modify if `Some`, this is only used to prevent computing the layout twice.
/// Avoids computing the layout of locals that are never actually initialized.
layout: Cell<Option<TyAndLayout<'tcx>>>,
}
impl<Prov: Provenance> std::fmt::Debug for LocalState<'_, Prov> {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.debug_struct("LocalState")
.field("value", &self.value)
.field("ty", &self.layout.get().map(|l| l.ty))
.finish()
}
}
/// Current value of a local variable
///
/// This does not store the type of the local; the type is given by `body.local_decls` and can never
/// change, so by not storing here we avoid having to maintain that as an invariant.
#[derive(Copy, Clone, Debug)] // Miri debug-prints these
pub(super) enum LocalValue<Prov: Provenance = CtfeProvenance> {
/// This local is not currently alive, and cannot be used at all.
Dead,
/// A normal, live local.
/// Mostly for convenience, we re-use the `Operand` type here.
/// This is an optimization over just always having a pointer here;
/// we can thus avoid doing an allocation when the local just stores
/// immediate values *and* never has its address taken.
Live(Operand<Prov>),
}
impl<'tcx, Prov: Provenance> LocalState<'tcx, Prov> {
pub fn make_live_uninit(&mut self) {
self.value = LocalValue::Live(Operand::Immediate(Immediate::Uninit));
}
/// This is a hack because Miri needs a way to visit all the provenance in a `LocalState`
/// without having a layout or `TyCtxt` available, and we want to keep the `Operand` type
/// private.
pub fn as_mplace_or_imm(
&self,
) -> Option<Either<(Pointer<Option<Prov>>, MemPlaceMeta<Prov>), Immediate<Prov>>> {
match self.value {
LocalValue::Dead => None,
LocalValue::Live(Operand::Indirect(mplace)) => Some(Left((mplace.ptr, mplace.meta))),
LocalValue::Live(Operand::Immediate(imm)) => Some(Right(imm)),
}
}
/// Read the local's value or error if the local is not yet live or not live anymore.
#[inline(always)]
pub(super) fn access(&self) -> InterpResult<'tcx, &Operand<Prov>> {
match &self.value {
LocalValue::Dead => throw_ub!(DeadLocal), // could even be "invalid program"?
LocalValue::Live(val) => Ok(val),
}
}
/// Overwrite the local. If the local can be overwritten in place, return a reference
/// to do so; otherwise return the `MemPlace` to consult instead.
#[inline(always)]
pub(super) fn access_mut(&mut self) -> InterpResult<'tcx, &mut Operand<Prov>> {
match &mut self.value {
LocalValue::Dead => throw_ub!(DeadLocal), // could even be "invalid program"?
LocalValue::Live(val) => Ok(val),
}
}
}
/// What we store about a frame in an interpreter backtrace.
#[derive(Clone, Debug)]
pub struct FrameInfo<'tcx> {
pub instance: ty::Instance<'tcx>,
pub span: Span,
}
// FIXME: only used by miri, should be removed once translatable.
impl<'tcx> fmt::Display for FrameInfo<'tcx> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
ty::tls::with(|tcx| {
if tcx.def_key(self.instance.def_id()).disambiguated_data.data == DefPathData::Closure {
write!(f, "inside closure")
} else {
// Note: this triggers a `must_produce_diag` state, which means that if we ever
// get here we must emit a diagnostic. We should never display a `FrameInfo` unless
// we actually want to emit a warning or error to the user.
write!(f, "inside `{}`", self.instance)
}
})
}
}
impl<'tcx> FrameInfo<'tcx> {
pub fn as_note(&self, tcx: TyCtxt<'tcx>) -> errors::FrameNote {
let span = self.span;
if tcx.def_key(self.instance.def_id()).disambiguated_data.data == DefPathData::Closure {
errors::FrameNote { where_: "closure", span, instance: String::new(), times: 0 }
} else {
let instance = format!("{}", self.instance);
// Note: this triggers a `must_produce_diag` state, which means that if we ever get
// here we must emit a diagnostic. We should never display a `FrameInfo` unless we
// actually want to emit a warning or error to the user.
errors::FrameNote { where_: "instance", span, instance, times: 0 }
}
}
}
impl<'tcx, Prov: Provenance> Frame<'tcx, Prov> {
pub fn with_extra<Extra>(self, extra: Extra) -> Frame<'tcx, Prov, Extra> {
Frame {
body: self.body,
instance: self.instance,
return_to_block: self.return_to_block,
return_place: self.return_place,
locals: self.locals,
loc: self.loc,
extra,
tracing_span: self.tracing_span,
}
}
}
impl<'tcx, Prov: Provenance, Extra> Frame<'tcx, Prov, Extra> {
/// Get the current location within the Frame.
///
/// If this is `Right`, we are not currently executing any particular statement in
/// this frame (can happen e.g. during frame initialization, and during unwinding on
/// frames without cleanup code).
///
/// Used by priroda.
pub fn current_loc(&self) -> Either<mir::Location, Span> {
self.loc
}
/// Return the `SourceInfo` of the current instruction.
pub fn current_source_info(&self) -> Option<&mir::SourceInfo> {
self.loc.left().map(|loc| self.body.source_info(loc))
}
pub fn current_span(&self) -> Span {
match self.loc {
Left(loc) => self.body.source_info(loc).span,
Right(span) => span,
}
}
pub fn lint_root(&self, tcx: TyCtxt<'tcx>) -> Option<hir::HirId> {
// We first try to get a HirId via the current source scope,
// and fall back to `body.source`.
self.current_source_info()
.and_then(|source_info| match &self.body.source_scopes[source_info.scope].local_data {
mir::ClearCrossCrate::Set(data) => Some(data.lint_root),
mir::ClearCrossCrate::Clear => None,
})
.or_else(|| {
let def_id = self.body.source.def_id().as_local();
def_id.map(|def_id| tcx.local_def_id_to_hir_id(def_id))
})
}
/// Returns the address of the buffer where the locals are stored. This is used by `Place` as a
/// sanity check to detect bugs where we mix up which stack frame a place refers to.
#[inline(always)]
pub(super) fn locals_addr(&self) -> usize {
self.locals.raw.as_ptr().addr()
}
#[must_use]
pub fn generate_stacktrace_from_stack(stack: &[Self]) -> Vec<FrameInfo<'tcx>> {
let mut frames = Vec::new();
// This deliberately does *not* honor `requires_caller_location` since it is used for much
// more than just panics.
for frame in stack.iter().rev() {
let span = match frame.loc {
Left(loc) => {
// If the stacktrace passes through MIR-inlined source scopes, add them.
let mir::SourceInfo { mut span, scope } = *frame.body.source_info(loc);
let mut scope_data = &frame.body.source_scopes[scope];
while let Some((instance, call_span)) = scope_data.inlined {
frames.push(FrameInfo { span, instance });
span = call_span;
scope_data = &frame.body.source_scopes[scope_data.parent_scope.unwrap()];
}
span
}
Right(span) => span,
};
frames.push(FrameInfo { span, instance: frame.instance });
}
trace!("generate stacktrace: {:#?}", frames);
frames
}
}
impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
/// Very low-level helper that pushes a stack frame without initializing
/// the arguments or local variables.
#[instrument(skip(self, body, return_place, return_to_block), level = "debug")]
pub(crate) fn push_stack_frame_raw(
&mut self,
instance: ty::Instance<'tcx>,
body: &'tcx mir::Body<'tcx>,
return_place: &MPlaceTy<'tcx, M::Provenance>,
return_to_block: StackPopCleanup,
) -> InterpResult<'tcx> {
trace!("body: {:#?}", body);
// We can push a `Root` frame if and only if the stack is empty.
debug_assert_eq!(
self.stack().is_empty(),
matches!(return_to_block, StackPopCleanup::Root { .. })
);
// First push a stack frame so we have access to `instantiate_from_current_frame` and other
// `self.frame()`-based functions.
let dead_local = LocalState { value: LocalValue::Dead, layout: Cell::new(None) };
let locals = IndexVec::from_elem(dead_local, &body.local_decls);
let pre_frame = Frame {
body,
loc: Right(body.span), // Span used for errors caused during preamble.
return_to_block,
return_place: return_place.clone(),
locals,
instance,
tracing_span: SpanGuard::new(),
extra: (),
};
let frame = M::init_frame(self, pre_frame)?;
self.stack_mut().push(frame);
// Make sure all the constants required by this frame evaluate successfully (post-monomorphization check).
for &const_ in body.required_consts() {
let c =
self.instantiate_from_current_frame_and_normalize_erasing_regions(const_.const_)?;
c.eval(*self.tcx, self.param_env, const_.span).map_err(|err| {
err.emit_note(*self.tcx);
err
})?;
}
// Finish things up.
M::after_stack_push(self)?;
self.frame_mut().loc = Left(mir::Location::START);
let span = info_span!("frame", "{}", instance);
self.frame_mut().tracing_span.enter(span);
Ok(())
}
/// Pops a stack frame from the stack and returns some information about it.
///
/// This also deallocates locals, if necessary.
///
/// [`M::before_stack_pop`] should be called before calling this function.
/// [`M::after_stack_pop`] is called by this function automatically.
///
/// [`M::before_stack_pop`]: Machine::before_stack_pop
/// [`M::after_stack_pop`]: Machine::after_stack_pop
pub(super) fn pop_stack_frame_raw(
&mut self,
unwinding: bool,
) -> InterpResult<'tcx, StackPopInfo<'tcx, M::Provenance>> {
let cleanup = self.cleanup_current_frame_locals()?;
let frame =
self.stack_mut().pop().expect("tried to pop a stack frame, but there were none");
let return_to_block = frame.return_to_block;
let return_place = frame.return_place.clone();
let return_action;
if cleanup {
return_action = M::after_stack_pop(self, frame, unwinding)?;
assert_ne!(return_action, ReturnAction::NoCleanup);
} else {
return_action = ReturnAction::NoCleanup;
};
Ok(StackPopInfo { return_action, return_to_block, return_place })
}
/// A private helper for [`pop_stack_frame_raw`](InterpCx::pop_stack_frame_raw).
/// Returns `true` if cleanup has been done, `false` otherwise.
fn cleanup_current_frame_locals(&mut self) -> InterpResult<'tcx, bool> {
// Cleanup: deallocate locals.
// Usually we want to clean up (deallocate locals), but in a few rare cases we don't.
// We do this while the frame is still on the stack, so errors point to the callee.
let return_to_block = self.frame().return_to_block;
let cleanup = match return_to_block {
StackPopCleanup::Goto { .. } => true,
StackPopCleanup::Root { cleanup, .. } => cleanup,
};
if cleanup {
// We need to take the locals out, since we need to mutate while iterating.
let locals = mem::take(&mut self.frame_mut().locals);
for local in &locals {
self.deallocate_local(local.value)?;
}
}
Ok(cleanup)
}
/// In the current stack frame, mark all locals as live that are not arguments and don't have
/// `Storage*` annotations (this includes the return place).
pub(crate) fn storage_live_for_always_live_locals(&mut self) -> InterpResult<'tcx> {
self.storage_live(mir::RETURN_PLACE)?;
let body = self.body();
let always_live = always_storage_live_locals(body);
for local in body.vars_and_temps_iter() {
if always_live.contains(local) {
self.storage_live(local)?;
}
}
Ok(())
}
pub fn storage_live_dyn(
&mut self,
local: mir::Local,
meta: MemPlaceMeta<M::Provenance>,
) -> InterpResult<'tcx> {
trace!("{:?} is now live", local);
// We avoid `ty.is_trivially_sized` since that does something expensive for ADTs.
fn is_very_trivially_sized(ty: Ty<'_>) -> bool {
match ty.kind() {
ty::Infer(ty::IntVar(_) | ty::FloatVar(_))
| ty::Uint(_)
| ty::Int(_)
| ty::Bool
| ty::Float(_)
| ty::FnDef(..)
| ty::FnPtr(_)
| ty::RawPtr(..)
| ty::Char
| ty::Ref(..)
| ty::Coroutine(..)
| ty::CoroutineWitness(..)
| ty::Array(..)
| ty::Closure(..)
| ty::CoroutineClosure(..)
| ty::Never
| ty::Error(_)
| ty::Dynamic(_, _, ty::DynStar) => true,
ty::Str | ty::Slice(_) | ty::Dynamic(_, _, ty::Dyn) | ty::Foreign(..) => false,
ty::Tuple(tys) => tys.last().is_none_or(|ty| is_very_trivially_sized(*ty)),
ty::Pat(ty, ..) => is_very_trivially_sized(*ty),
// We don't want to do any queries, so there is not much we can do with ADTs.
ty::Adt(..) => false,
ty::Alias(..) | ty::Param(_) | ty::Placeholder(..) => false,
ty::Infer(ty::TyVar(_)) => false,
ty::Bound(..)
| ty::Infer(ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => {
bug!("`is_very_trivially_sized` applied to unexpected type: {}", ty)
}
}
}
// This is a hot function, we avoid computing the layout when possible.
// `unsized_` will be `None` for sized types and `Some(layout)` for unsized types.
let unsized_ = if is_very_trivially_sized(self.body().local_decls[local].ty) {
None
} else {
// We need the layout.
let layout = self.layout_of_local(self.frame(), local, None)?;
if layout.is_sized() { None } else { Some(layout) }
};
let local_val = LocalValue::Live(if let Some(layout) = unsized_ {
if !meta.has_meta() {
throw_unsup!(UnsizedLocal);
}
// Need to allocate some memory, since `Immediate::Uninit` cannot be unsized.
let dest_place = self.allocate_dyn(layout, MemoryKind::Stack, meta)?;
Operand::Indirect(*dest_place.mplace())
} else {
assert!(!meta.has_meta()); // we're dropping the metadata
// Just make this an efficient immediate.
// Note that not calling `layout_of` here does have one real consequence:
// if the type is too big, we'll only notice this when the local is actually initialized,
// which is a bit too late -- we should ideally notice this already here, when the memory
// is conceptually allocated. But given how rare that error is and that this is a hot function,
// we accept this downside for now.
Operand::Immediate(Immediate::Uninit)
});
// If the local is already live, deallocate its old memory.
let old = mem::replace(&mut self.frame_mut().locals[local].value, local_val);
self.deallocate_local(old)?;
Ok(())
}
/// Mark a storage as live, killing the previous content.
#[inline(always)]
pub fn storage_live(&mut self, local: mir::Local) -> InterpResult<'tcx> {
self.storage_live_dyn(local, MemPlaceMeta::None)
}
pub fn storage_dead(&mut self, local: mir::Local) -> InterpResult<'tcx> {
assert!(local != mir::RETURN_PLACE, "Cannot make return place dead");
trace!("{:?} is now dead", local);
// If the local is already dead, this is a NOP.
let old = mem::replace(&mut self.frame_mut().locals[local].value, LocalValue::Dead);
self.deallocate_local(old)?;
Ok(())
}
fn deallocate_local(&mut self, local: LocalValue<M::Provenance>) -> InterpResult<'tcx> {
if let LocalValue::Live(Operand::Indirect(MemPlace { ptr, .. })) = local {
// All locals have a backing allocation, even if the allocation is empty
// due to the local having ZST type. Hence we can `unwrap`.
trace!(
"deallocating local {:?}: {:?}",
local,
// Locals always have a `alloc_id` (they are never the result of a int2ptr).
self.dump_alloc(ptr.provenance.unwrap().get_alloc_id().unwrap())
);
self.deallocate_ptr(ptr, None, MemoryKind::Stack)?;
};
Ok(())
}
#[inline(always)]
pub(super) fn layout_of_local(
&self,
frame: &Frame<'tcx, M::Provenance, M::FrameExtra>,
local: mir::Local,
layout: Option<TyAndLayout<'tcx>>,
) -> InterpResult<'tcx, TyAndLayout<'tcx>> {
let state = &frame.locals[local];
if let Some(layout) = state.layout.get() {
return Ok(layout);
}
let layout = from_known_layout(self.tcx, self.param_env, layout, || {
let local_ty = frame.body.local_decls[local].ty;
let local_ty =
self.instantiate_from_frame_and_normalize_erasing_regions(frame, local_ty)?;
self.layout_of(local_ty)
})?;
// Layouts of locals are requested a lot, so we cache them.
state.layout.set(Some(layout));
Ok(layout)
}
}
impl<'tcx, Prov: Provenance> LocalState<'tcx, Prov> {
pub(super) fn print(
&self,
allocs: &mut Vec<Option<AllocId>>,
fmt: &mut std::fmt::Formatter<'_>,
) -> std::fmt::Result {
match self.value {
LocalValue::Dead => write!(fmt, " is dead")?,
LocalValue::Live(Operand::Immediate(Immediate::Uninit)) => {
write!(fmt, " is uninitialized")?
}
LocalValue::Live(Operand::Indirect(mplace)) => {
write!(
fmt,
" by {} ref {:?}:",
match mplace.meta {
MemPlaceMeta::Meta(meta) => format!(" meta({meta:?})"),
MemPlaceMeta::None => String::new(),
},
mplace.ptr,
)?;
allocs.extend(mplace.ptr.provenance.map(Provenance::get_alloc_id));
}
LocalValue::Live(Operand::Immediate(Immediate::Scalar(val))) => {
write!(fmt, " {val:?}")?;
if let Scalar::Ptr(ptr, _size) = val {
allocs.push(ptr.provenance.get_alloc_id());
}
}
LocalValue::Live(Operand::Immediate(Immediate::ScalarPair(val1, val2))) => {
write!(fmt, " ({val1:?}, {val2:?})")?;
if let Scalar::Ptr(ptr, _size) = val1 {
allocs.push(ptr.provenance.get_alloc_id());
}
if let Scalar::Ptr(ptr, _size) = val2 {
allocs.push(ptr.provenance.get_alloc_id());
}
}
}
Ok(())
}
}