Rollup merge of #125582 - scottmcm:less-from-usize, r=jieyouxu

Avoid a `FieldIdx::from_usize` in InstSimplify
Just a tiny cleanup I noticed in passing while looking at something unrelated.

Author: workingjubilee

compiler/rustc_mir_transform/src/dataflow_const_prop.rs

@@ -142,10 +142,10 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'_, 'tcx> {
  _ => return,
 };
 ifletSome(variant_target_idx) = variant_target {
-for(field_index, operand)in operands.iter().enumerate(){
+for(field_index, operand)in operands.iter_enumerated(){
 ifletSome(field) = self.map().apply(
  variant_target_idx,
-TrackElem::Field(FieldIdx::from_usize(field_index)),
+TrackElem::Field(field_index),
 ){
 self.assign_operand(state, field, operand);
 }

compiler/rustc_mir_transform/src/instsimplify.rs

@@ -9,7 +9,6 @@ use rustc_middle::ty::layout::ValidityRequirement;
 use rustc_middle::ty::{self,GenericArgsRef,ParamEnv,Ty,TyCtxt};
 use rustc_span::sym;
 use rustc_span::symbol::Symbol;
-use rustc_target::abi::FieldIdx;
 use rustc_target::spec::abi::Abi;
 
 pubstructInstSimplify;
@@ -217,11 +216,11 @@ impl<'tcx> InstSimplifyContext<'tcx, '_> {
  && letSome(place) = operand.place()
 {
 let variant = adt_def.non_enum_variant();
-for(i, field)in variant.fields.iter().enumerate(){
+for(i, field)in variant.fields.iter_enumerated(){
 let field_ty = field.ty(self.tcx, args);
 if field_ty == *cast_ty {
 let place = place.project_deeper(
-&[ProjectionElem::Field(FieldIdx::from_usize(i),*cast_ty)],
+&[ProjectionElem::Field(i,*cast_ty)],
 self.tcx,
 );
 let operand = if operand.is_move(){