Stop deaggegating MIR.

compiler/rustc_const_eval/src/util/aggregate.rs

@@ -1,77 +0,0 @@
-use rustc_index::vec::Idx;
-use rustc_middle::mir::*;
-use rustc_middle::ty::{Ty, TyCtxt};
-use rustc_target::abi::VariantIdx;
-
-use std::iter::TrustedLen;
-
-/// Expand `lhs = Rvalue::Aggregate(kind, operands)` into assignments to the fields.
-///
-/// Produces something like
-/// ```ignore (ilustrative)
-/// (lhs as Variant).field0 = arg0;     // We only have a downcast if this is an enum
-/// (lhs as Variant).field1 = arg1;
-/// discriminant(lhs) = variant_index;  // If lhs is an enum or generator.
-/// ```
-pub fn expand_aggregate<'tcx>(
-    orig_lhs: Place<'tcx>,
-    operands: impl Iterator<Item = (Operand<'tcx>, Ty<'tcx>)> + TrustedLen,
-    kind: AggregateKind<'tcx>,
-    source_info: SourceInfo,
-    tcx: TyCtxt<'tcx>,
-) -> impl Iterator<Item = Statement<'tcx>> + TrustedLen {
-    let mut lhs = orig_lhs;
-    let mut set_discriminant = None;
-    let active_field_index = match kind {
-        AggregateKind::Adt(adt_did, variant_index, _, _, active_field_index) => {
-            let adt_def = tcx.adt_def(adt_did);
-            if adt_def.is_enum() {
-                set_discriminant = Some(Statement {
-                    kind: StatementKind::SetDiscriminant {
-                        place: Box::new(orig_lhs),
-                        variant_index,
-                    },
-                    source_info,
-                });
-                lhs = tcx.mk_place_downcast(orig_lhs, adt_def, variant_index);
-            }
-            active_field_index
-        }
-        AggregateKind::Generator(..) => {
-            // Right now we only support initializing generators to
-            // variant 0 (Unresumed).
-            let variant_index = VariantIdx::new(0);
-            set_discriminant = Some(Statement {
-                kind: StatementKind::SetDiscriminant { place: Box::new(orig_lhs), variant_index },
-                source_info,
-            });
-
-            // Operands are upvars stored on the base place, so no
-            // downcast is necessary.
-
-            None
-        }
-        _ => None,
-    };
-
-    let operands = operands.enumerate().map(move |(i, (op, ty))| {
-        let lhs_field = if let AggregateKind::Array(_) = kind {
-            let offset = u64::try_from(i).unwrap();
-            tcx.mk_place_elem(
-                lhs,
-                ProjectionElem::ConstantIndex { offset, min_length: offset + 1, from_end: false },
-            )
-        } else {
-            let field = Field::new(active_field_index.unwrap_or(i));
-            tcx.mk_place_field(lhs, field, ty)
-        };
-        Statement {
-            source_info,
-            kind: StatementKind::Assign(Box::new((lhs_field, Rvalue::Use(op)))),
-        }
-    });
-    [Statement { source_info, kind: StatementKind::Deinit(Box::new(orig_lhs)) }]
-        .into_iter()
-        .chain(operands)
-        .chain(set_discriminant)
-}

compiler/rustc_const_eval/src/util/mod.rs

@@ -1,4 +1,3 @@
-pub mod aggregate;
 mod alignment;
 mod call_kind;
 pub mod collect_writes;
@@ -7,7 +6,6 @@
 mod might_permit_raw_init;
 mod type_name;
 
-pub use self::aggregate::expand_aggregate;
 pub use self::alignment::is_disaligned;
 pub use self::call_kind::{call_kind, CallDesugaringKind, CallKind};
 pub use self::compare_types::{is_equal_up_to_subtyping, is_subtype};

compiler/rustc_mir_transform/src/deaggregator.rs

@@ -1,49 +0,0 @@
-use crate::util::expand_aggregate;
-use crate::MirPass;
-use rustc_hir::def::DefKind;
-use rustc_middle::mir::*;
-use rustc_middle::ty::TyCtxt;
-
-pub struct Deaggregator;
-
-impl<'tcx> MirPass<'tcx> for Deaggregator {
-    fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-        let basic_blocks = body.basic_blocks.as_mut_preserves_cfg();
-        for bb in basic_blocks {
-            bb.expand_statements(|stmt| {
-                // FIXME(eddyb) don't match twice on `stmt.kind` (post-NLL).
-                let StatementKind::Assign(box (
-                    _, Rvalue::Aggregate(box ref kind, _))
-                ) = stmt.kind else { return None };
-
-                // FIXME(#48193) Deaggregate arrays when it's cheaper to do so.
-                if let AggregateKind::Array(_) = kind {
-                    return None;
-                }
-
-                if let AggregateKind::Adt(def_id, ..) = kind
-                    && matches!(tcx.def_kind(def_id), DefKind::Enum)
-                {
-                    return None;
-                }
-
-                let stmt = stmt.replace_nop();
-                let source_info = stmt.source_info;
-                let StatementKind::Assign(box (lhs, Rvalue::Aggregate(kind, operands))) = stmt.kind else {
-                    bug!();
-                };
-
-                Some(expand_aggregate(
-                    lhs,
-                    operands.into_iter().map(|op| {
-                        let ty = op.ty(&body.local_decls, tcx);
-                        (op, ty)
-                    }),
-                    *kind,
-                    source_info,
-                    tcx,
-                ))
-            });
-        }
-    }
-}

compiler/rustc_mir_transform/src/lib.rs

@@ -60,7 +60,6 @@
 mod ctfe_limit;
 mod dataflow_const_prop;
 mod dead_store_elimination;
-mod deaggregator;
 mod deduce_param_attrs;
 mod deduplicate_blocks;
 mod deref_separator;
@@ -523,9 +522,6 @@ fn run_runtime_lowering_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         &elaborate_box_derefs::ElaborateBoxDerefs,
         &generator::StateTransform,
         &add_retag::AddRetag,
-        // Deaggregator is necessary for const prop. We may want to consider implementing
-        // CTFE support for aggregates.
-        &deaggregator::Deaggregator,
         &Lint(const_prop_lint::ConstProp),
     ];
     pm::run_passes_no_validate(tcx, body, passes, Some(MirPhase::Runtime(RuntimePhase::Initial)));