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Rollup merge of rust-lang#91410 - ecstatic-morse:const-precise-live-d…
…rops-take-2, r=oli-obk Move `#![feature(const_precise_live_drops)]` checks earlier in the pipeline Should mitigate the issues found during MCP on rust-lang#73255. Once this is done, we should clean up the queries a bit, since I think `mir_drops_elaborated_and_const_checked` can be merged back into `mir_promoted`. Fixes rust-lang#90770. cc `@rust-lang/wg-const-eval` r? `@nikomatsakis` (since they reviewed rust-lang#71824)
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,29 @@ | ||
| use rustc_middle::mir::{Body, TerminatorKind}; | ||
| use rustc_middle::ty::TyCtxt; | ||
|
|
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| use crate::MirPass; | ||
|
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| /// Removes `FalseEdge` and `FalseUnwind` terminators from the MIR. | ||
| /// | ||
| /// These are only needed for borrow checking, and can be removed afterwards. | ||
| /// | ||
| /// FIXME: This should probably have its own MIR phase. | ||
| pub struct RemoveFalseEdges; | ||
|
|
||
| impl<'tcx> MirPass<'tcx> for RemoveFalseEdges { | ||
| fn run_pass(&self, _: TyCtxt<'tcx>, body: &mut Body<'tcx>) { | ||
| for block in body.basic_blocks_mut() { | ||
| let terminator = block.terminator_mut(); | ||
| terminator.kind = match terminator.kind { | ||
| TerminatorKind::FalseEdge { real_target, .. } => { | ||
| TerminatorKind::Goto { target: real_target } | ||
| } | ||
| TerminatorKind::FalseUnwind { real_target, .. } => { | ||
| TerminatorKind::Goto { target: real_target } | ||
| } | ||
|
|
||
| _ => continue, | ||
| } | ||
| } | ||
| } | ||
| } |
171 changes: 171 additions & 0 deletions
171
compiler/rustc_mir_transform/src/remove_uninit_drops.rs
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,171 @@ | ||
| use rustc_index::bit_set::BitSet; | ||
| use rustc_middle::mir::{Body, Field, Rvalue, Statement, StatementKind, TerminatorKind}; | ||
| use rustc_middle::ty::subst::SubstsRef; | ||
| use rustc_middle::ty::{self, ParamEnv, Ty, TyCtxt, VariantDef}; | ||
| use rustc_mir_dataflow::impls::MaybeInitializedPlaces; | ||
| use rustc_mir_dataflow::move_paths::{LookupResult, MoveData, MovePathIndex}; | ||
| use rustc_mir_dataflow::{self, move_path_children_matching, Analysis, MoveDataParamEnv}; | ||
|
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| use crate::MirPass; | ||
|
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| /// Removes `Drop` and `DropAndReplace` terminators whose target is known to be uninitialized at | ||
| /// that point. | ||
| /// | ||
| /// This is redundant with drop elaboration, but we need to do it prior to const-checking, and | ||
| /// running const-checking after drop elaboration makes it opimization dependent, causing issues | ||
| /// like [#90770]. | ||
| /// | ||
| /// [#90770]: https://github.com/rust-lang/rust/issues/90770 | ||
| pub struct RemoveUninitDrops; | ||
|
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| impl<'tcx> MirPass<'tcx> for RemoveUninitDrops { | ||
| fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) { | ||
| let param_env = tcx.param_env(body.source.def_id()); | ||
| let Ok(move_data) = MoveData::gather_moves(body, tcx, param_env) else { | ||
| // We could continue if there are move errors, but there's not much point since our | ||
| // init data isn't complete. | ||
| return; | ||
| }; | ||
|
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||
| let mdpe = MoveDataParamEnv { move_data, param_env }; | ||
| let mut maybe_inits = MaybeInitializedPlaces::new(tcx, body, &mdpe) | ||
| .into_engine(tcx, body) | ||
| .pass_name("remove_uninit_drops") | ||
| .iterate_to_fixpoint() | ||
| .into_results_cursor(body); | ||
|
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||
| let mut to_remove = vec![]; | ||
| for (bb, block) in body.basic_blocks().iter_enumerated() { | ||
| let terminator = block.terminator(); | ||
| let (TerminatorKind::Drop { place, .. } | TerminatorKind::DropAndReplace { place, .. }) | ||
| = &terminator.kind | ||
| else { continue }; | ||
|
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| maybe_inits.seek_before_primary_effect(body.terminator_loc(bb)); | ||
|
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| // If there's no move path for the dropped place, it's probably a `Deref`. Let it alone. | ||
| let LookupResult::Exact(mpi) = mdpe.move_data.rev_lookup.find(place.as_ref()) else { | ||
| continue; | ||
| }; | ||
|
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||
| let should_keep = is_needs_drop_and_init( | ||
| tcx, | ||
| param_env, | ||
| maybe_inits.get(), | ||
| &mdpe.move_data, | ||
| place.ty(body, tcx).ty, | ||
| mpi, | ||
| ); | ||
| if !should_keep { | ||
| to_remove.push(bb) | ||
| } | ||
| } | ||
|
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| for bb in to_remove { | ||
| let block = &mut body.basic_blocks_mut()[bb]; | ||
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| let (TerminatorKind::Drop { target, .. } | TerminatorKind::DropAndReplace { target, .. }) | ||
| = &block.terminator().kind | ||
| else { unreachable!() }; | ||
|
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| // Replace block terminator with `Goto`. | ||
| let target = *target; | ||
| let old_terminator_kind = std::mem::replace( | ||
| &mut block.terminator_mut().kind, | ||
| TerminatorKind::Goto { target }, | ||
| ); | ||
|
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||
| // If this is a `DropAndReplace`, we need to emulate the assignment to the return place. | ||
| if let TerminatorKind::DropAndReplace { place, value, .. } = old_terminator_kind { | ||
| block.statements.push(Statement { | ||
| source_info: block.terminator().source_info, | ||
| kind: StatementKind::Assign(Box::new((place, Rvalue::Use(value)))), | ||
| }); | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
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||
| fn is_needs_drop_and_init( | ||
| tcx: TyCtxt<'tcx>, | ||
| param_env: ParamEnv<'tcx>, | ||
| maybe_inits: &BitSet<MovePathIndex>, | ||
| move_data: &MoveData<'tcx>, | ||
| ty: Ty<'tcx>, | ||
| mpi: MovePathIndex, | ||
| ) -> bool { | ||
| // No need to look deeper if the root is definitely uninit or if it has no `Drop` impl. | ||
| if !maybe_inits.contains(mpi) || !ty.needs_drop(tcx, param_env) { | ||
| return false; | ||
| } | ||
|
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| let field_needs_drop_and_init = |(f, f_ty, mpi)| { | ||
| let child = move_path_children_matching(move_data, mpi, |x| x.is_field_to(f)); | ||
| let Some(mpi) = child else { | ||
| return f_ty.needs_drop(tcx, param_env); | ||
| }; | ||
|
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| is_needs_drop_and_init(tcx, param_env, maybe_inits, move_data, f_ty, mpi) | ||
| }; | ||
|
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| // This pass is only needed for const-checking, so it doesn't handle as many cases as | ||
| // `DropCtxt::open_drop`, since they aren't relevant in a const-context. | ||
| match ty.kind() { | ||
| ty::Adt(adt, substs) => { | ||
| let dont_elaborate = adt.is_union() || adt.is_manually_drop() || adt.has_dtor(tcx); | ||
| if dont_elaborate { | ||
| return true; | ||
| } | ||
|
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||
| // Look at all our fields, or if we are an enum all our variants and their fields. | ||
| // | ||
| // If a field's projection *is not* present in `MoveData`, it has the same | ||
| // initializedness as its parent (maybe init). | ||
| // | ||
| // If its projection *is* present in `MoveData`, then the field may have been moved | ||
| // from separate from its parent. Recurse. | ||
| adt.variants.iter_enumerated().any(|(vid, variant)| { | ||
| // Enums have multiple variants, which are discriminated with a `Downcast` projection. | ||
| // Structs have a single variant, and don't use a `Downcast` projection. | ||
| let mpi = if adt.is_enum() { | ||
| let downcast = | ||
| move_path_children_matching(move_data, mpi, |x| x.is_downcast_to(vid)); | ||
| let Some(dc_mpi) = downcast else { | ||
| return variant_needs_drop(tcx, param_env, substs, variant); | ||
| }; | ||
|
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| dc_mpi | ||
| } else { | ||
| mpi | ||
| }; | ||
|
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| variant | ||
| .fields | ||
| .iter() | ||
| .enumerate() | ||
| .map(|(f, field)| (Field::from_usize(f), field.ty(tcx, substs), mpi)) | ||
| .any(field_needs_drop_and_init) | ||
| }) | ||
| } | ||
|
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| ty::Tuple(_) => ty | ||
| .tuple_fields() | ||
| .enumerate() | ||
| .map(|(f, f_ty)| (Field::from_usize(f), f_ty, mpi)) | ||
| .any(field_needs_drop_and_init), | ||
|
|
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| _ => true, | ||
| } | ||
| } | ||
|
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| fn variant_needs_drop( | ||
| tcx: TyCtxt<'tcx>, | ||
| param_env: ParamEnv<'tcx>, | ||
| substs: SubstsRef<'tcx>, | ||
| variant: &VariantDef, | ||
| ) -> bool { | ||
| variant.fields.iter().any(|field| { | ||
| let f_ty = field.ty(tcx, substs); | ||
| f_ty.needs_drop(tcx, param_env) | ||
| }) | ||
| } |
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4 changes: 2 additions & 2 deletions
4
...in.SimplifyBranches-after-const-prop.diff → ...plifyConstCondition-after-const-prop.diff
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2 changes: 1 addition & 1 deletion
2
....before-SimplifyBranches-final.after.diff → ...e-SimplifyConstCondition-final.after.diff
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4 changes: 2 additions & 2 deletions
4
...in.SimplifyBranches-after-const-prop.diff → ...plifyConstCondition-after-const-prop.diff
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