rustc_index: Add a `ZERO` constant to index types

It is commonly used.

5 files changed, 17 insertions, 21 deletions

diff --git a/compiler/rustc_mir_transform/src/coroutine.rs b/compiler/rustc_mir_transform/src/coroutine.rs
index c3f175f150d..e2a911f0dc7 100644
--- a/compiler/rustc_mir_transform/src/coroutine.rs
+++ b/compiler/rustc_mir_transform/src/coroutine.rs
@@ -168,7 +168,7 @@ impl<'tcx> MutVisitor<'tcx> for PinArgVisitor<'tcx> {
                 Place {
                     local: SELF_ARG,
                     projection: self.tcx().mk_place_elems(&[ProjectionElem::Field(
-                        FieldIdx::new(0),
+                        FieldIdx::ZERO,
                         self.ref_coroutine_ty,
                     )]),
                 },
@@ -267,7 +267,7 @@ impl<'tcx> TransformVisitor<'tcx> {
                 Rvalue::Aggregate(
                     Box::new(AggregateKind::Adt(
                         option_def_id,
-                        VariantIdx::from_usize(0),
+                        VariantIdx::ZERO,
                         self.tcx.mk_args(&[self.old_yield_ty.into()]),
                         None,
                         None,
@@ -329,7 +329,7 @@ impl<'tcx> TransformVisitor<'tcx> {
                     Rvalue::Aggregate(
                         Box::new(AggregateKind::Adt(
                             poll_def_id,
-                            VariantIdx::from_usize(0),
+                            VariantIdx::ZERO,
                             args,
                             None,
                             None,
@@ -358,7 +358,7 @@ impl<'tcx> TransformVisitor<'tcx> {
                     Rvalue::Aggregate(
                         Box::new(AggregateKind::Adt(
                             option_def_id,
-                            VariantIdx::from_usize(0),
+                            VariantIdx::ZERO,
                             args,
                             None,
                             None,
@@ -420,7 +420,7 @@ impl<'tcx> TransformVisitor<'tcx> {
                     Rvalue::Aggregate(
                         Box::new(AggregateKind::Adt(
                             coroutine_state_def_id,
-                            VariantIdx::from_usize(0),
+                            VariantIdx::ZERO,
                             args,
                             None,
                             None,
diff --git a/compiler/rustc_mir_transform/src/elaborate_box_derefs.rs b/compiler/rustc_mir_transform/src/elaborate_box_derefs.rs
index 96943435bab..318674f24e7 100644
--- a/compiler/rustc_mir_transform/src/elaborate_box_derefs.rs
+++ b/compiler/rustc_mir_transform/src/elaborate_box_derefs.rs
@@ -3,7 +3,6 @@
 //! Box is not actually a pointer so it is incorrect to dereference it directly.
 
 use rustc_hir::def_id::DefId;
-use rustc_index::Idx;
 use rustc_middle::mir::patch::MirPatch;
 use rustc_middle::mir::visit::MutVisitor;
 use rustc_middle::mir::*;
@@ -32,9 +31,9 @@ pub fn build_projection<'tcx>(
     ptr_ty: Ty<'tcx>,
 ) -> [PlaceElem<'tcx>; 3] {
     [
-        PlaceElem::Field(FieldIdx::new(0), unique_ty),
-        PlaceElem::Field(FieldIdx::new(0), nonnull_ty),
-        PlaceElem::Field(FieldIdx::new(0), ptr_ty),
+        PlaceElem::Field(FieldIdx::ZERO, unique_ty),
+        PlaceElem::Field(FieldIdx::ZERO, nonnull_ty),
+        PlaceElem::Field(FieldIdx::ZERO, ptr_ty),
     ]
 }
 
@@ -91,15 +90,14 @@ pub struct ElaborateBoxDerefs;
 impl<'tcx> MirPass<'tcx> for ElaborateBoxDerefs {
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
         if let Some(def_id) = tcx.lang_items().owned_box() {
-            let unique_did =
-                tcx.adt_def(def_id).non_enum_variant().fields[FieldIdx::from_u32(0)].did;
+            let unique_did = tcx.adt_def(def_id).non_enum_variant().fields[FieldIdx::ZERO].did;
 
             let Some(nonnull_def) = tcx.type_of(unique_did).instantiate_identity().ty_adt_def()
             else {
                 span_bug!(tcx.def_span(unique_did), "expected Box to contain Unique")
             };
 
-            let nonnull_did = nonnull_def.non_enum_variant().fields[FieldIdx::from_u32(0)].did;
+            let nonnull_did = nonnull_def.non_enum_variant().fields[FieldIdx::ZERO].did;
 
             let patch = MirPatch::new(body);
 
diff --git a/compiler/rustc_mir_transform/src/gvn.rs b/compiler/rustc_mir_transform/src/gvn.rs
index 59d6d89cf1f..d4f736d2a50 100644
--- a/compiler/rustc_mir_transform/src/gvn.rs
+++ b/compiler/rustc_mir_transform/src/gvn.rs
@@ -355,7 +355,7 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
     }
 
     fn insert_tuple(&mut self, values: Vec<VnIndex>) -> VnIndex {
-        self.insert(Value::Aggregate(AggregateTy::Tuple, VariantIdx::from_u32(0), values))
+        self.insert(Value::Aggregate(AggregateTy::Tuple, VariantIdx::ZERO, values))
     }
 
     #[instrument(level = "trace", skip(self), ret)]
diff --git a/compiler/rustc_mir_transform/src/known_panics_lint.rs b/compiler/rustc_mir_transform/src/known_panics_lint.rs
index a20958e74df..2218154ea5e 100644
--- a/compiler/rustc_mir_transform/src/known_panics_lint.rs
+++ b/compiler/rustc_mir_transform/src/known_panics_lint.rs
@@ -13,7 +13,7 @@ use rustc_const_eval::interpret::{
 use rustc_data_structures::fx::FxHashSet;
 use rustc_hir::def::DefKind;
 use rustc_hir::HirId;
-use rustc_index::{bit_set::BitSet, Idx, IndexVec};
+use rustc_index::{bit_set::BitSet, IndexVec};
 use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor};
 use rustc_middle::mir::*;
 use rustc_middle::ty::layout::{LayoutError, LayoutOf, LayoutOfHelpers, TyAndLayout};
@@ -124,10 +124,8 @@ impl<'tcx> Value<'tcx> {
                     fields.ensure_contains_elem(*idx, || Value::Uninit)
                 }
                 (PlaceElem::Field(..), val @ Value::Uninit) => {
-                    *val = Value::Aggregate {
-                        variant: VariantIdx::new(0),
-                        fields: Default::default(),
-                    };
+                    *val =
+                        Value::Aggregate { variant: VariantIdx::ZERO, fields: Default::default() };
                     val.project_mut(&[*proj])?
                 }
                 _ => return None,
@@ -572,7 +570,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
                     self.use_ecx(|this| this.ecx.overflowing_binary_op(bin_op, &left, &right))?;
                 let overflowed = ImmTy::from_bool(overflowed, self.tcx);
                 Value::Aggregate {
-                    variant: VariantIdx::new(0),
+                    variant: VariantIdx::ZERO,
                     fields: [Value::from(val), overflowed.into()].into_iter().collect(),
                 }
             }
@@ -607,7 +605,7 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
                         | AggregateKind::Tuple
                         | AggregateKind::Closure(_, _)
                         | AggregateKind::Coroutine(_, _)
-                        | AggregateKind::CoroutineClosure(_, _) => VariantIdx::new(0),
+                        | AggregateKind::CoroutineClosure(_, _) => VariantIdx::ZERO,
                     },
                 }
             }
diff --git a/compiler/rustc_mir_transform/src/simplify.rs b/compiler/rustc_mir_transform/src/simplify.rs
index 14772080ce5..5bbe3bb747f 100644
--- a/compiler/rustc_mir_transform/src/simplify.rs
+++ b/compiler/rustc_mir_transform/src/simplify.rs
@@ -415,7 +415,7 @@ fn make_local_map<V>(
     used_locals: &UsedLocals,
 ) -> IndexVec<Local, Option<Local>> {
     let mut map: IndexVec<Local, Option<Local>> = IndexVec::from_elem(None, local_decls);
-    let mut used = Local::new(0);
+    let mut used = Local::ZERO;
 
     for alive_index in local_decls.indices() {
         // `is_used` treats the `RETURN_PLACE` and arguments as used.