Use FieldIdx in various things related to aggregates

Shrank `AggregateKind` by 8 bytes on x64, since the active field of a union is tracked as an `Option<FieldIdx>` instead of `Option<usize>`.

compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -6,6 +6,7 @@ use rustc_errors::{Applicability, Diagnostic};
 use rustc_hir as hir;
 use rustc_hir::def::{CtorKind, Namespace};
 use rustc_hir::GeneratorKind;
+use rustc_index::vec::IndexSlice;
 use rustc_infer::infer::{LateBoundRegionConversionTime, TyCtxtInferExt};
 use rustc_middle::mir::tcx::PlaceTy;
 use rustc_middle::mir::{
@@ -825,7 +826,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     debug!("move_spans: def_id={:?} place={:?}", closure_def_id, place);
                     let places = &[Operand::Move(place)];
                     if let Some((args_span, generator_kind, capture_kind_span, path_span)) =
-                        self.closure_span(closure_def_id, moved_place, places)
+                        self.closure_span(closure_def_id, moved_place, IndexSlice::from_raw(places))
                     {
                         return ClosureUse {
                             generator_kind,
@@ -975,7 +976,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         &self,
         def_id: LocalDefId,
         target_place: PlaceRef<'tcx>,
-        places: &[Operand<'tcx>],
+        places: &IndexSlice<FieldIdx, Operand<'tcx>>,
     ) -> Option<(Span, Option<GeneratorKind>, Span, Span)> {
         debug!(
             "closure_span: def_id={:?} target_place={:?} places={:?}",

compiler/rustc_borrowck/src/lib.rs

@@ -1343,7 +1343,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                             self.infcx.tcx.mir_borrowck(def_id);
                         debug!("{:?} used_mut_upvars={:?}", def_id, used_mut_upvars);
                         for field in used_mut_upvars {
-                            self.propagate_closure_used_mut_upvar(&operands[field.index()]);
+                            self.propagate_closure_used_mut_upvar(&operands[*field]);
                         }
                     }
                     AggregateKind::Adt(..)

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -14,7 +14,7 @@ use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::LocalDefId;
 use rustc_hir::lang_items::LangItem;
-use rustc_index::vec::IndexVec;
+use rustc_index::vec::{IndexSlice, IndexVec};
 use rustc_infer::infer::canonical::QueryRegionConstraints;
 use rustc_infer::infer::outlives::env::RegionBoundPairs;
 use rustc_infer::infer::region_constraints::RegionConstraintData;
@@ -1716,7 +1716,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
     fn aggregate_field_ty(
         &mut self,
         ak: &AggregateKind<'tcx>,
-        field_index: usize,
+        field_index: FieldIdx,
         location: Location,
     ) -> Result<Ty<'tcx>, FieldAccessError> {
         let tcx = self.tcx();
@@ -1725,16 +1725,15 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             AggregateKind::Adt(adt_did, variant_index, substs, _, active_field_index) => {
                 let def = tcx.adt_def(adt_did);
                 let variant = &def.variant(variant_index);
-                let adj_field_index =
-                    FieldIdx::from_usize(active_field_index.unwrap_or(field_index));
+                let adj_field_index = active_field_index.unwrap_or(field_index);
                 if let Some(field) = variant.fields.get(adj_field_index) {
                     Ok(self.normalize(field.ty(tcx, substs), location))
                 } else {
                     Err(FieldAccessError::OutOfRange { field_count: variant.fields.len() })
                 }
             }
             AggregateKind::Closure(_, substs) => {
-                match substs.as_closure().upvar_tys().nth(field_index) {
+                match substs.as_closure().upvar_tys().nth(field_index.as_usize()) {
                     Some(ty) => Ok(ty),
                     None => Err(FieldAccessError::OutOfRange {
                         field_count: substs.as_closure().upvar_tys().count(),
@@ -1745,7 +1744,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                 // It doesn't make sense to look at a field beyond the prefix;
                 // these require a variant index, and are not initialized in
                 // aggregate rvalues.
-                match substs.as_generator().prefix_tys().nth(field_index) {
+                match substs.as_generator().prefix_tys().nth(field_index.as_usize()) {
                     Some(ty) => Ok(ty),
                     None => Err(FieldAccessError::OutOfRange {
                         field_count: substs.as_generator().prefix_tys().count(),
@@ -2350,7 +2349,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
         body: &Body<'tcx>,
         rvalue: &Rvalue<'tcx>,
         aggregate_kind: &AggregateKind<'tcx>,
-        operands: &[Operand<'tcx>],
+        operands: &IndexSlice<FieldIdx, Operand<'tcx>>,
         location: Location,
     ) {
         let tcx = self.tcx();
@@ -2362,16 +2361,16 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             return;
         }
 
-        for (i, operand) in operands.iter().enumerate() {
+        for (i, operand) in operands.iter_enumerated() {
             let field_ty = match self.aggregate_field_ty(aggregate_kind, i, location) {
                 Ok(field_ty) => field_ty,
                 Err(FieldAccessError::OutOfRange { field_count }) => {
                     span_mirbug!(
                         self,
                         rvalue,
                         "accessed field #{} but variant only has {}",
-                        i,
-                        field_count
+                        i.as_u32(),
+                        field_count,
                     );
                     continue;
                 }

compiler/rustc_codegen_cranelift/src/base.rs

@@ -802,14 +802,15 @@ fn codegen_stmt<'tcx>(
                     if active_field_index.is_some() {
                         assert_eq!(operands.len(), 1);
                     }
-                    for (i, operand) in operands.iter().enumerate() {
+                    for (i, operand) in operands.iter_enumerated() {
                         let operand = codegen_operand(fx, operand);
                         let field_index = active_field_index.unwrap_or(i);
                         let to = if let mir::AggregateKind::Array(_) = **kind {
-                            let index = fx.bcx.ins().iconst(fx.pointer_type, field_index as i64);
+                            let array_index = i64::from(field_index.as_u32());
+                            let index = fx.bcx.ins().iconst(fx.pointer_type, array_index);
                             variant_dest.place_index(fx, index)
                         } else {
-                            variant_dest.place_field(fx, FieldIdx::new(field_index))
+                            variant_dest.place_field(fx, field_index)
                         };
                         to.write_cvalue(fx, operand);
                     }

compiler/rustc_codegen_ssa/src/base.rs

@@ -306,9 +306,9 @@ pub fn coerce_unsized_into<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
         (&ty::Adt(def_a, _), &ty::Adt(def_b, _)) => {
             assert_eq!(def_a, def_b);
 
-            for i in 0..def_a.variant(FIRST_VARIANT).fields.len() {
-                let src_f = src.project_field(bx, i);
-                let dst_f = dst.project_field(bx, i);
+            for i in def_a.variant(FIRST_VARIANT).fields.indices() {
+                let src_f = src.project_field(bx, i.as_usize());
+                let dst_f = dst.project_field(bx, i.as_usize());
 
                 if dst_f.layout.is_zst() {
                     continue;

compiler/rustc_codegen_ssa/src/mir/rvalue.rs

@@ -123,16 +123,16 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 if active_field_index.is_some() {
                     assert_eq!(operands.len(), 1);
                 }
-                for (i, operand) in operands.iter().enumerate() {
+                for (i, operand) in operands.iter_enumerated() {
                     let op = self.codegen_operand(bx, operand);
                     // Do not generate stores and GEPis for zero-sized fields.
                     if !op.layout.is_zst() {
                         let field_index = active_field_index.unwrap_or(i);
                         let field = if let mir::AggregateKind::Array(_) = **kind {
-                            let llindex = bx.cx().const_usize(field_index as u64);
+                            let llindex = bx.cx().const_usize(field_index.as_u32().into());
                             variant_dest.project_index(bx, llindex)
                         } else {
-                            variant_dest.project_field(bx, field_index)
+                            variant_dest.project_field(bx, field_index.as_usize())
                         };
                         op.val.store(bx, field);
                     }

compiler/rustc_const_eval/src/interpret/place.rs

@@ -5,10 +5,11 @@
 use either::{Either, Left, Right};
 
 use rustc_ast::Mutability;
+use rustc_index::vec::IndexSlice;
 use rustc_middle::mir;
 use rustc_middle::ty;
 use rustc_middle::ty::layout::{LayoutOf, TyAndLayout};
-use rustc_target::abi::{self, Abi, Align, HasDataLayout, Size, FIRST_VARIANT};
+use rustc_target::abi::{self, Abi, Align, FieldIdx, HasDataLayout, Size, FIRST_VARIANT};
 
 use super::{
     alloc_range, mir_assign_valid_types, AllocId, AllocRef, AllocRefMut, CheckInAllocMsg,
@@ -787,7 +788,7 @@ where
     pub fn write_aggregate(
         &mut self,
         kind: &mir::AggregateKind<'tcx>,
-        operands: &[mir::Operand<'tcx>],
+        operands: &IndexSlice<FieldIdx, mir::Operand<'tcx>>,
         dest: &PlaceTy<'tcx, M::Provenance>,
     ) -> InterpResult<'tcx> {
         self.write_uninit(&dest)?;
@@ -801,9 +802,9 @@ where
         if active_field_index.is_some() {
             assert_eq!(operands.len(), 1);
         }
-        for (field_index, operand) in operands.iter().enumerate() {
+        for (field_index, operand) in operands.iter_enumerated() {
             let field_index = active_field_index.unwrap_or(field_index);
-            let field_dest = self.place_field(&variant_dest, field_index)?;
+            let field_dest = self.place_field(&variant_dest, field_index.as_usize())?;
             let op = self.eval_operand(operand, Some(field_dest.layout))?;
             self.copy_op(&op, &field_dest, /*allow_transmute*/ false)?;
         }

compiler/rustc_index/src/vec.rs

@@ -93,6 +93,12 @@ impl<I: Idx, T: fmt::Debug> fmt::Debug for IndexVec<I, T> {
     }
 }
 
+impl<I: Idx, T: fmt::Debug> fmt::Debug for IndexSlice<I, T> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&self.raw, fmt)
+    }
+}
+
 impl<I: Idx, T> IndexVec<I, T> {
     #[inline]
     pub fn new() -> Self {

compiler/rustc_middle/src/mir/syntax.rs

@@ -16,6 +16,7 @@ use rustc_ast::{InlineAsmOptions, InlineAsmTemplatePiece};
 use rustc_hir::def_id::DefId;
 use rustc_hir::{self as hir};
 use rustc_hir::{self, GeneratorKind};
+use rustc_index::vec::IndexVec;
 use rustc_target::abi::{FieldIdx, VariantIdx};
 
 use rustc_ast::Mutability;
@@ -1125,7 +1126,7 @@ pub enum Rvalue<'tcx> {
     ///
     /// Disallowed after deaggregation for all aggregate kinds except `Array` and `Generator`. After
     /// generator lowering, `Generator` aggregate kinds are disallowed too.
-    Aggregate(Box<AggregateKind<'tcx>>, Vec<Operand<'tcx>>),
+    Aggregate(Box<AggregateKind<'tcx>>, IndexVec<FieldIdx, Operand<'tcx>>),
 
     /// Transmutes a `*mut u8` into shallow-initialized `Box<T>`.
     ///
@@ -1186,7 +1187,7 @@ pub enum AggregateKind<'tcx> {
     /// active field number and is present only for union expressions
     /// -- e.g., for a union expression `SomeUnion { c: .. }`, the
     /// active field index would identity the field `c`
-    Adt(DefId, VariantIdx, SubstsRef<'tcx>, Option<UserTypeAnnotationIndex>, Option<usize>),
+    Adt(DefId, VariantIdx, SubstsRef<'tcx>, Option<UserTypeAnnotationIndex>, Option<FieldIdx>),
 
     Closure(DefId, SubstsRef<'tcx>),
     Generator(DefId, SubstsRef<'tcx>, hir::Movability),
@@ -1263,7 +1264,7 @@ pub enum BinOp {
 mod size_asserts {
     use super::*;
     // tidy-alphabetical-start
-    static_assert_size!(AggregateKind<'_>, 40);
+    static_assert_size!(AggregateKind<'_>, 32);
     static_assert_size!(Operand<'_>, 24);
     static_assert_size!(Place<'_>, 16);
     static_assert_size!(PlaceElem<'_>, 24);

compiler/rustc_mir_build/src/build/custom/parse/instruction.rs

@@ -185,7 +185,7 @@ impl<'tcx, 'body> ParseCtxt<'tcx, 'body> {
             },
             ExprKind::Adt(box AdtExpr{ adt_def, variant_index, substs, fields, .. }) => {
                 let is_union = adt_def.is_union();
-                let active_field_index = is_union.then(|| fields[0].name.index());
+                let active_field_index = is_union.then(|| fields[0].name);
 
                 Ok(Rvalue::Aggregate(
                     Box::new(AggregateKind::Adt(adt_def.did(), *variant_index, substs, None, active_field_index)),

compiler/rustc_mir_build/src/build/expr/as_rvalue.rs

@@ -1,8 +1,8 @@
 //! See docs in `build/expr/mod.rs`.
 
-use rustc_index::vec::Idx;
+use rustc_index::vec::{Idx, IndexVec};
 use rustc_middle::ty::util::IntTypeExt;
-use rustc_target::abi::{Abi, Primitive};
+use rustc_target::abi::{Abi, FieldIdx, Primitive};
 
 use crate::build::expr::as_place::PlaceBase;
 use crate::build::expr::category::{Category, RvalueFunc};
@@ -17,7 +17,6 @@ use rustc_middle::thir::*;
 use rustc_middle::ty::cast::{mir_cast_kind, CastTy};
 use rustc_middle::ty::{self, Ty, UpvarSubsts};
 use rustc_span::Span;
-use rustc_target::abi::FieldIdx;
 
 impl<'a, 'tcx> Builder<'a, 'tcx> {
     /// Returns an rvalue suitable for use until the end of the current
@@ -327,7 +326,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
                 // first process the set of fields
                 let el_ty = expr.ty.sequence_element_type(this.tcx);
-                let fields: Vec<_> = fields
+                let fields: IndexVec<FieldIdx, _> = fields
                     .into_iter()
                     .copied()
                     .map(|f| {
@@ -348,7 +347,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             ExprKind::Tuple { ref fields } => {
                 // see (*) above
                 // first process the set of fields
-                let fields: Vec<_> = fields
+                let fields: IndexVec<FieldIdx, _> = fields
                     .into_iter()
                     .copied()
                     .map(|f| {
@@ -402,7 +401,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 }
 
                 // see (*) above
-                let operands: Vec<_> = upvars
+                let operands: IndexVec<FieldIdx, _> = upvars
                     .into_iter()
                     .copied()
                     .map(|upvar| {
@@ -710,7 +709,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             }
             this.record_operands_moved(&[value_operand]);
         }
-        block.and(Rvalue::Aggregate(Box::new(AggregateKind::Array(elem_ty)), Vec::new()))
+        block.and(Rvalue::Aggregate(Box::new(AggregateKind::Array(elem_ty)), IndexVec::new()))
     }
 
     fn limit_capture_mutability(

compiler/rustc_mir_build/src/build/expr/into.rs

@@ -6,11 +6,9 @@ use rustc_ast::InlineAsmOptions;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_hir as hir;
-use rustc_index::vec::Idx;
 use rustc_middle::mir::*;
 use rustc_middle::thir::*;
 use rustc_middle::ty::CanonicalUserTypeAnnotation;
-use rustc_target::abi::FieldIdx;
 use std::iter;
 
 impl<'a, 'tcx> Builder<'a, 'tcx> {
@@ -320,7 +318,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 // See the notes for `ExprKind::Array` in `as_rvalue` and for
                 // `ExprKind::Borrow` above.
                 let is_union = adt_def.is_union();
-                let active_field_index = is_union.then(|| fields[0].name.index());
+                let active_field_index = is_union.then(|| fields[0].name);
 
                 let scope = this.local_scope();
 
@@ -344,10 +342,9 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     })
                     .collect();
 
-                let field_names: Vec<_> =
-                    (0..adt_def.variant(variant_index).fields.len()).map(FieldIdx::new).collect();
+                let field_names = adt_def.variant(variant_index).fields.indices();
 
-                let fields: Vec<_> = if let Some(FruInfo { base, field_types }) = base {
+                let fields = if let Some(FruInfo { base, field_types }) = base {
                     let place_builder =
                         unpack!(block = this.as_place_builder(block, &this.thir[*base]));
 
@@ -364,7 +361,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                         })
                         .collect()
                 } else {
-                    field_names.iter().filter_map(|n| fields_map.get(n).cloned()).collect()
+                    field_names.filter_map(|n| fields_map.get(&n).cloned()).collect()
                 };
 
                 let inferred_ty = expr.ty;

compiler/rustc_mir_transform/src/generator.rs

@@ -274,7 +274,7 @@ impl<'tcx> TransformVisitor<'tcx> {
             statements.push(Statement {
                 kind: StatementKind::Assign(Box::new((
                     Place::return_place(),
-                    Rvalue::Aggregate(Box::new(kind), vec![]),
+                    Rvalue::Aggregate(Box::new(kind), IndexVec::new()),
                 ))),
                 source_info,
             });
@@ -287,7 +287,7 @@ impl<'tcx> TransformVisitor<'tcx> {
         statements.push(Statement {
             kind: StatementKind::Assign(Box::new((
                 Place::return_place(),
-                Rvalue::Aggregate(Box::new(kind), vec![val]),
+                Rvalue::Aggregate(Box::new(kind), IndexVec::from_iter([val])),
             ))),
             source_info,
         });