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Auto merge of #112307 - lcnr:operand-ref, r=compiler-errors

mir opt + codegen: handle subtyping

fixes #107205

the same issue was caused in multiple places:
- mir opts: both copy and destination propagation
- codegen: assigning operands to locals (which also propagates values)

I changed codegen to always update the type in the operands used for locals which should guard against any new occurrences of this bug going forward. I don't know how to make mir optimizations more resilient here. Hopefully the added tests will be enough to detect any trivially wrong optimizations going forward.
This commit is contained in:
bors 2023-06-28 00:41:37 +00:00
commit bb95b7dcd6
12 changed files with 207 additions and 39 deletions

View file

@ -37,6 +37,10 @@
//! if they do not consistently refer to the same place in memory. This is satisfied if they do
//! not contain any indirection through a pointer or any indexing projections.
//!
//! * `p` and `q` must have the **same type**. If we replace a local with a subtype or supertype,
//! we may end up with a differnet vtable for that local. See the `subtyping-impacts-selection`
//! tests for an example where that causes issues.
//!
//! * We need to make sure that the goal of "merging the memory" is actually structurally possible
//! in MIR. For example, even if all the other conditions are satisfied, there is no way to
//! "merge" `_5.foo` and `_6.bar`. For now, we ensure this by requiring that both `p` and `q` are
@ -134,6 +138,7 @@ use crate::MirPass;
use rustc_data_structures::fx::FxHashMap;
use rustc_index::bit_set::BitSet;
use rustc_middle::mir::visit::{MutVisitor, PlaceContext, Visitor};
use rustc_middle::mir::HasLocalDecls;
use rustc_middle::mir::{dump_mir, PassWhere};
use rustc_middle::mir::{
traversal, Body, InlineAsmOperand, Local, LocalKind, Location, Operand, Place, Rvalue,
@ -763,12 +768,22 @@ impl<'tcx> Visitor<'tcx> for FindAssignments<'_, '_, 'tcx> {
return;
};
// As described at the top of the file, we do not go near things that have their address
// taken.
// As described at the top of the file, we do not go near things that have
// their address taken.
if self.borrowed.contains(src) || self.borrowed.contains(dest) {
return;
}
// As described at the top of this file, we do not touch locals which have
// different types.
let src_ty = self.body.local_decls()[src].ty;
let dest_ty = self.body.local_decls()[dest].ty;
if src_ty != dest_ty {
// FIXME(#112651): This can be removed afterwards. Also update the module description.
trace!("skipped `{src:?} = {dest:?}` due to subtyping: {src_ty} != {dest_ty}");
return;
}
// Also, we need to make sure that MIR actually allows the `src` to be removed
if is_local_required(src, self.body) {
return;

View file

@ -32,13 +32,15 @@ fn make_shim<'tcx>(tcx: TyCtxt<'tcx>, instance: ty::InstanceDef<'tcx>) -> Body<'
let mut result = match instance {
ty::InstanceDef::Item(..) => bug!("item {:?} passed to make_shim", instance),
ty::InstanceDef::VTableShim(def_id) => {
build_call_shim(tcx, instance, Some(Adjustment::Deref), CallKind::Direct(def_id))
let adjustment = Adjustment::Deref { source: DerefSource::MutPtr };
build_call_shim(tcx, instance, Some(adjustment), CallKind::Direct(def_id))
}
ty::InstanceDef::FnPtrShim(def_id, ty) => {
let trait_ = tcx.trait_of_item(def_id).unwrap();
let adjustment = match tcx.fn_trait_kind_from_def_id(trait_) {
Some(ty::ClosureKind::FnOnce) => Adjustment::Identity,
Some(ty::ClosureKind::FnMut | ty::ClosureKind::Fn) => Adjustment::Deref,
Some(ty::ClosureKind::Fn) => Adjustment::Deref { source: DerefSource::ImmRef },
Some(ty::ClosureKind::FnMut) => Adjustment::Deref { source: DerefSource::MutRef },
None => bug!("fn pointer {:?} is not an fn", ty),
};
@ -107,16 +109,26 @@ fn make_shim<'tcx>(tcx: TyCtxt<'tcx>, instance: ty::InstanceDef<'tcx>) -> Body<'
result
}
#[derive(Copy, Clone, Debug, PartialEq)]
enum DerefSource {
/// `fn shim(&self) { inner(*self )}`.
ImmRef,
/// `fn shim(&mut self) { inner(*self )}`.
MutRef,
/// `fn shim(*mut self) { inner(*self )}`.
MutPtr,
}
#[derive(Copy, Clone, Debug, PartialEq)]
enum Adjustment {
/// Pass the receiver as-is.
Identity,
/// We get passed `&[mut] self` and call the target with `*self`.
/// We get passed a reference or a raw pointer to `self` and call the target with `*self`.
///
/// This either copies `self` (if `Self: Copy`, eg. for function items), or moves out of it
/// (for `VTableShim`, which effectively is passed `&own Self`).
Deref,
Deref { source: DerefSource },
/// We get passed `self: Self` and call the target with `&mut self`.
///
@ -667,8 +679,12 @@ fn build_call_shim<'tcx>(
let self_arg = &mut inputs_and_output[0];
*self_arg = match rcvr_adjustment.unwrap() {
Adjustment::Identity => fnty,
Adjustment::Deref => tcx.mk_imm_ptr(fnty),
Adjustment::RefMut => tcx.mk_mut_ptr(fnty),
Adjustment::Deref { source } => match source {
DerefSource::ImmRef => tcx.mk_imm_ref(tcx.lifetimes.re_erased, fnty),
DerefSource::MutRef => tcx.mk_mut_ref(tcx.lifetimes.re_erased, fnty),
DerefSource::MutPtr => tcx.mk_mut_ptr(fnty),
},
Adjustment::RefMut => bug!("`RefMut` is never used with indirect calls: {instance:?}"),
};
sig.inputs_and_output = tcx.mk_type_list(&inputs_and_output);
}
@ -699,7 +715,7 @@ fn build_call_shim<'tcx>(
let rcvr = rcvr_adjustment.map(|rcvr_adjustment| match rcvr_adjustment {
Adjustment::Identity => Operand::Move(rcvr_place()),
Adjustment::Deref => Operand::Move(tcx.mk_place_deref(rcvr_place())),
Adjustment::Deref { source: _ } => Operand::Move(tcx.mk_place_deref(rcvr_place())),
Adjustment::RefMut => {
// let rcvr = &mut rcvr;
let ref_rcvr = local_decls.push(

View file

@ -271,6 +271,14 @@ fn compute_copy_classes(ssa: &mut SsaLocals, body: &Body<'_>) {
else { continue };
let Some(rhs) = place.as_local() else { continue };
let local_ty = body.local_decls()[local].ty;
let rhs_ty = body.local_decls()[rhs].ty;
if local_ty != rhs_ty {
// FIXME(#112651): This can be removed afterwards.
trace!("skipped `{local:?} = {rhs:?}` due to subtyping: {local_ty} != {rhs_ty}");
continue;
}
if !ssa.is_ssa(rhs) {
continue;
}