don't convert types to the same type with try_into (clippy::useless_conversion)

compiler/rustc_mir/src/dataflow/move_paths/builder.rs

@@ -4,7 +4,6 @@ use rustc_middle::mir::*;
 use rustc_middle::ty::{self, TyCtxt};
 use smallvec::{smallvec, SmallVec};
 
-use std::convert::TryInto;
 use std::mem;
 
 use super::abs_domain::Lift;
@@ -482,10 +481,8 @@ impl<'b, 'a, 'tcx> Gatherer<'b, 'a, 'tcx> {
             let base_ty = base_place.ty(self.builder.body, self.builder.tcx).ty;
             let len: u64 = match base_ty.kind() {
                 ty::Array(_, size) => {
-                    let length = size.eval_usize(self.builder.tcx, self.builder.param_env);
+                    let length: u64 = size.eval_usize(self.builder.tcx, self.builder.param_env);
                     length
-                        .try_into()
-                        .expect("slice pattern of array with more than u32::MAX elements")
                 }
                 _ => bug!("from_end: false slice pattern of non-array type"),
             };

compiler/rustc_mir/src/interpret/place.rs

@@ -551,7 +551,7 @@ where
                 let n = base.len(self)?;
                 if n < min_length {
                     // This can only be reached in ConstProp and non-rustc-MIR.
-                    throw_ub!(BoundsCheckFailed { len: min_length.into(), index: n });
+                    throw_ub!(BoundsCheckFailed { len: min_length, index: n });
                 }
 
                 let index = if from_end {
@@ -565,9 +565,7 @@ where
                 self.mplace_index(base, index)?
             }
 
-            Subslice { from, to, from_end } => {
-                self.mplace_subslice(base, u64::from(from), u64::from(to), from_end)?
-            }
+            Subslice { from, to, from_end } => self.mplace_subslice(base, from, to, from_end)?,
         })
     }
 

compiler/rustc_mir_build/src/build/matches/util.rs

@@ -33,7 +33,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         let tcx = self.hir.tcx();
         let (min_length, exact_size) = match place.ty(&self.local_decls, tcx).ty.kind() {
             ty::Array(_, length) => {
-                (length.eval_usize(tcx, self.hir.param_env).try_into().unwrap(), true)
+                (length.eval_usize(tcx, self.hir.param_env), true)
             }
             _ => ((prefix.len() + suffix.len()).try_into().unwrap(), false),
         };